Free Schematic Diagram

Modular Burglar Alarm Circuit

2011-09-27T11:05:00.000+07:00

In this figure is design circuit for modular burglar alarm circuit. This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. This circuit is connected permanently to the 12-volt supply and its operation is “enabled” by opening SW1. By using the expansion modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type.

All the green LEDs should be lighting before you open SW1. You then have up to about a minute to leave the building. As you do so, the Buzzer will sound. It should stop sounding when you shut the door behind you. This indicates that the Exit/Entry loop has been successfully restored within the time allowed. When you re-enter the building you have up to about a minute to move SW1 to the off position.

If SW1 is not switched off in time, the relay will energize and sound the main bell. It will ring for up to about 40 minutes. But it can be turned off at any time by SW1.However, it’s much easier to find a fault when the alarm is divided into zones and the control panel can remember which zone has caused the activation.

Frequency/Tone Decoder Circuit Using TC9400 FVC

2011-09-27T10:58:00.000+07:00

Another application of FVC (frequency-to-voltage converter) is tone/frequency decoder. This circuit is used to determine the frequency band of an oscillation signal. This circuit is used in many application like determines the frequency band in the signal and remote control where the frequency band corresponds to a different command. This circuit uses TC9400 F/V converter to convert the frequency to voltage because the frequency must be converted to proportional analog voltage before can be detected. This is the figure of the circuit;

Beside TC9400 F/V converter, this circuit also uses the quad comparators. It used to detect when the frequency limits is exceeded by the voltage (frequency). The frequency is indicated by the logical “1″ at any of the five output. [Circuit diagram source: Microchip Application Note]

1000W Power Inverter Circuit

2011-09-27T10:56:00.000+07:00

Here’s a circuit for the power inverter circuit based MOSFET RFP50N06. The inverter capable to handle loads up to 1000W, it’s depended on your power inverter transformer. Here’s the figure of the circuit;

The RFP50N06 Fets are rated at 50 Amps and 60 Volts. Heat sink is required for cooling the MOSFETs. You may add some MOSFETs with parallel connection to get more power. It is recommended to have a “Fuse” in the Power Line and to always have a “Load connected”, while power is being applied.

1Hz up to 22MHz Generator Using MAX038

2011-09-25T14:17:00.000+07:00

This is a design circuit for simple MAX038 generator. It produces sine, triangle and square waves from 1Hz up to 22MHz. The Amplitude, offset and duty cycle are adjustable to offer wide range of generated signals. This is the figure of the circuit;

Frequency adjustment is made as a rotary switch S8 with a capacitor bank and variable resistor P7. Amplitude, offset and duty-cycle are performed via variable resistors. Switch S5 selects generated waveform. The output at U1-19 is 2V p-p for all waveforms. For amplitude adjustment, P6 and R38 form a voltage divider. The summing amplifier multiplies that voltage, so the signal at the output will vary up tp 24.4V p-p. The offset voltage is controlled by resistor P5. Duty-cycle adjustment is controlled by resistor P4.

Ultrasonic Motion Detector Circuit

2011-08-27T11:35:00.000+07:00

Here’s a design circuit for a ultrasonic motion detector (or movement detector) circuit. The circuit claimed has a high movement sensitivity. Even air moving (hot air rising, wind blowing) will trigger it when the trimpot is set near the most sensitive position. This is the figure of the circuit;

The transmitter sends out a steady ultrasonic tone at 40 kHz. At this frequency the wavelength is about 6 mm. Any reflected sound is detected by ultrasonic receiver. The signal is then amplified by IC1: A and IC1:B. IC1:A is self biasing via C2 & R5. The time constant of the first amplifier is set to let the 40 kHz signal through. Between the first & second amplifier there is a negative peak detector (diode D1 & R8) which follows the envelope of the 40 kHz signal. If there is no movement the envelope is just a straight line. The time constant of IC1: B is much slower so that it will follow this envelope. All the amplifiers are AC coupled to prevent DC bias problems.

TDA7056 3W BTL Mono Audio Power Amplifier Circuit

2011-08-27T11:32:00.000+07:00

Here’s a design circuit for mono output amplifier application, TDA7056 IC can be your option. Compact but powerful, this integrated circuit is contained in a 9 pin medium power package. This device is designed for battery fed portable equipments such as mono recorders, radios and television. This is the figure of the circuit;

To attract the market, TDA7056 has many features such as low power consumption. For more reliable operation, TDA7056 also has short circuit proof and ESD (Electro Static Discharge) protected on all pins. Designing application with this IC should be easy since no external components is needed. To make sure you’ll love this chip, this device also has no switch on/off clicks. Overall, TDA7056 has good stability. [Circuit schematic diagram source: Philips Semiconductors Datasheet]

Stable Zener Reference Circuit

2011-08-27T11:30:00.000+07:00

Nowadays some first-rate voltage references are available. Take the LM385 for example: this is available for different voltages and even comes in an adjustable version. What is more, the current consumption may be kept very small (10 µA). But as often happens, you may not have one to hand when you need one for an experimental circuit. In that case, you could use an ordinary zener diode for the reference. Unfortunately, they have a somewhat higher internal resistance (about 5?), which means they won’t be very stable when the supply voltage varies. The solution is right in front of us: use the stabilized zener voltage as the supply voltage! This is obviously only possible if the stabilized voltage is higher than the zener voltage. This is the figure of the circuit of stable zener reference;

It therefore has to be amplified a little. This is exactly what this circuit does: it amplifies it by a factor of two. The current limiting resister should be chosen such that a current of 1 to 3 mA flows through the zener diode. Manufacturers usually state the zener voltage at a current between 3 to 5 mA. The zener diode is fed from a stabilized voltage and hence has a very stable operating point, which is independent from the supply voltage. The graph speaks for itself. It is clear that the output voltage is much more stable. The graphs have been plotted to different scales to make the comparison easier. In reality the op amp output is twice the zener voltage. Zener diodes also have a temperature coefficient, which is smallest for types with a zener voltage around 5 volts. Virtually any type of opamp should be suitable; even our old friend the 741 works well enough.

Square Root Mode for AD532 Analog Processor

2011-08-27T11:27:00.000+07:00

Here’s a design circuit for about the connections for square root mode for ADS532 analog processor chip. Similar to the division mode, the multiplier cell is connected in the feedback of the op amp by connecting the output back to both the X and Y inputs. This is the figure of the circuit;

To prevent latch up as Zi approaches 0 Volts, the diode D1 is connected. The Vov adjustment is made with Zin = +0.1 V dc in this case, adjusting Vos to obtain -1.0 V dc in the output, Vout =-√(10 VZ). Gain (S.F) and offset (Xo) adjustments are recommended for optimum performance.

Tachometer Circuit Using LM2907 LM2917 Frequency to Voltage Converter

2011-08-20T10:42:00.000+07:00

This is a design circuit for tachometer circuit based on the LM2907 IC can be used to provide zero crossing datum to a digital system. At each zero crossing of the input signal the charge pump changes the state of capacitor C1 and provides a one-shot pulse into the zener diode at pin 3. The width of this pulse is controlled by the internal current of pin 2 and the size of capacitor C1 as well as by the supply voltage. This is the figure of the circuit;

Since a pulse is generated by each zero crossing of the input signal we call this a ``two-shot'' instead of a ``one-shot'' device and this can be used for doubling the frequency that is presented to the microprocessor control system. This electronic tachometer circuit project can be powered from a 12, 15 volt DC power supply circuit. Input can be from plus /minus 20 mV to plus/minus 28V. Pulse width is equal with (VCC/2)x(C1/I2) and the Pulse height is equal with VZENER.

LTC3588-1 Piezoelectric Energy Harvesting Power Supply Circuit

2011-08-20T10:41:00.000+07:00

Here’s a design circuit of The LTC3588-1 is a piezoelectric energy harvesting power supply IC that integrates a low-loss full-wave bridge rectifier with a high efficiency buck converter to form a complete energy harvesting solution optimized for high output impedance energy sources such as piezoelectric transducers. This is the figure of the circuit;

LTC3588-1 can be configured to deliver four output voltages: 1.8V, 2.5V, 3.3V and 3.6V. In this table you can see how you need to configure the pins of the LTC3588-1 to obtain the specified voltage. To select Low for D0, D1 the pin must be connected to GND and if you need to select high for D0, D2 the pin must be connected to VIN2. The maximum output current can be set up to 100mA. As you can see in this power schematic circuit the design of power supply is very easy and require few external components. A power supply circuit based on the LTC3588-1 IC offers many features like: 950nA Input Quiescent Current (Output in Regulation – No Load) , 450nA Input Quiescent Current in UVLO, 2.7V to 20V Input Operating Range, Integrated Low-Loss Full-Wave Bridge Rectifier, Up to 100mA of Output Current, Selectable Output Voltages, High Efficiency Integrated Hysteretic Buck DC/DC.

The LTC3588-1 IC can be used in many applications circuits like: Piezoelectric Energy Harvesting, Electro-Mechanical Energy Harvesting, Wireless HVAC Sensors, Mobile Asset Tracking, Tire Pressure Sensors, Battery Replacement for Industrial Sensors, Remote Light Switches.

Frequency/Tone Decoder Circuit Using TC9400 FVC

2011-08-20T10:40:00.000+07:00

Audio Monitoring Circuit

2011-05-19T02:58:00.000+07:00

This is a design schematic of audio monitoring system which the transmitter will pickup sound from one location and the receiver at other location will reproduce it. The receiver and transmitter of the circuit is connected by one set of wire. And in here the power supply and transmitted signal is share in the same wire. This is a figure for a complete design schematic.

The operation of the circuit is the audio signals picked up by the microphone will be amplified by the double stage amplifier build around transistors Q1 and Q2.The POT R2 controls gain of the amplifier. The power supply for this circuit is drawn from the interconnection lines itself. The capacitor C4 bypasses all audio frequencies & noise from the line and ensures pure DC for the circuit. The output of the amplifier (audio signal) is coupled to the line via the capacitor C6. At the receiver end the capacitor C7 extracts the audio signal from the line and feds it to the inverting input of IC1 (TL071) which is wired as a voltage amplifier. Output of IC1 is given to the input of IC2 (LM386) which is a integrated power amplifier.IC2 provided necessary current gain to drive the speaker. The POT R14 can be used control the gain of receiver. Capacitor C11 isolates audio frequencies and noise from the power supply of both the ICs.

Pre Amplifier Circuit for Oscilloscope

2011-05-19T02:53:00.000+07:00

An oscilloscope amplifier with 20 dB voltage gain is provided by this circuit with a frequency range from 0.5 to 50 MHz. By increasing the value of the 0.05 uF capacitor or try removing the capacitor, we can extend the low frequency response of this circuit. This is the figure of the circuit;

A particularly small level of input noise is delivered by this circuit, measured at approximately 20uA over a bandwidth range at 15 MHz. By adjusting the gain potentiometer connected between pins 3 and 10, then adjust the 1-KΩ trimmer potentiometer for an exact voltage gain of 10 are the ways to calibrate the gain. This helps preserve the scale factor of the oscilloscope.

MAX2664/MAX2665 VHF UHF Low Noise Amplifiers Circuit

2011-05-19T02:48:00.000+07:00

Here’s a design circuit for very simple low cost and ultra compact VHF UHF Low-Noise amplifiers circuit can be designed using the MAX2664 and MAX2665 ultra-compact LNAs for VHF/UHF applications. These devices incorporate a broadband LNA with an integrated bypass switch. The MAX2664 covers the UHF frequency range from 470MHz to 860MHz, and the MAX2665 covers the VHF frequency range from 75MHz to 230MHz. Each device has a zero-power bypass mode for improved high-signal-level handling conditions. This is the figure of the circuit;

As you can see in the presented circuit diagram, this RF project requires very few external components . Both ICs has a high gain around 15dB and require a single power supply, that can provide an output voltage between 2.4 to 3.5 volts. VHF UHF Low-Noise amplifiers has a very low current consumption of 3.3 mA and can be used in applications like: Smart phones/Handsets , MP3 Players , Home Audio/Video and other portable navigation devices.

9 Sec Timer Using LED Indication And Control Relay Circuit

2011-05-19T02:32:00.000+07:00

The electronic circuit provides a visual time 9 second delay using ten LED before control by closing a 12 Vdc relay. That the reset switch has closed, IC 4017 decade counter will be reset to zero count which illuminates the LED driven from pin 3. Here’s the figure of the circuit;

IC 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 Vdc. That time the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the IC 555 timer circuit to produce an approximate one second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with most capacitor or most resistor at pins 2 and 6 of the IC 555 timer

Single Chip Stereo FM Transmitter Circuit

2011-04-19T19:28:00.000+07:00

ROHM (www.rohm.com) is originally a resistor producer company, but finally expand their business and produce monolithic IC, and this one used in our circuit is the example. The internal structure of this FM transmitter integrated circuit consist of stereo modulator that creates a stereo composite signal, an FM modulator that modulate a carrier frequency with the composite signal, and an RF amplifier that provide enough power to be transmitted through antenna. This is the figure of the circuit;

The core of this stereo FM transmitter is BA1404 integrated circuit chip. from ROHM. This FM transmitter is ideal for wireless microphone, or for audio interface and distribution for home or car appliance. For example, you can now play your portable mp3/mp4 player on your old car radio sound system that doesn’t have line-input plug. This stereo FM transmitter chip is designed for 75-108 FM band, and you can adjust the operation by trimming the LC network connected to pin 10 of this IC chip. To ease the adjustment, you can use a 22-33p variable capacitor for the 15p capacitor connected to pin 10. Finally, this stereo FM transmitter works with only 1.5-3V power supply, ideal for battery operation. More than 3.5V supply voltage could burn this FM transmitter circuit. [Circuit diagram source: ROHM Application Notes]

2 Phase and 3 Phase Motor Drivers Circuit

2011-04-19T19:22:00.000+07:00

Here’s a design circuit for 2-phase and 3-phase motor driver circuits. This circuit can used to drive an AC motor because this circuit has an integrated power operational amplifier, built-in power-output stage and high amplification factor. The needed AC signal is produced by the op amp that is configured as oscillator. The motor is driven by the high-current that is supplied from the power output stage. The another op amp is configured as Wien bridge oscillator. This is the figure of the circuit;

The oscillation frequency is determined by following equation:

f0=1/(2π*squareroot(R1*R2*C1*C2))

The upper schematic diagram is the 2-phase motor driver, while the lower schematic is the diagram of 3-phase motor driver circuit. The oscillator frequency can be adjusted to a narrow range by varying R2 or R1. The signal attenuation which occurs in the phase shifters is compensated by the second amplifier’s gain. The second amplifier’s gain is set by R3/R4 ratio. The output of this circuit is sinusoidal because of RC feedback networks that used as an active filters. An external source like square wave or pulse can be used to drive this circuit. [Circuit's diagram source: seekic.com]

Enabling 3 Phase Motor to Operates Using Single Phase Supply

2011-04-13T08:00:00.000+07:00

Capacitor have been use for decades to operate 3-phase motors on single-phase power. Two single-phase wires are connected to two of the inputs on a 3 phase motor on this method. Then, the capacitors is connected to one of the single -phase inputs and the third leg of the motor. This is the figure of the circuit;

The voltage is allowed to be displaced in time from its parent voltage by phase shift through the capacitor. Voltage distinct from the 2 single-phase lines is the result. The motor will operate if the capacitors value-it’s ability to process electrical current- is sufficient. 6 times as much current to start as it does to run is required by the motor so a static-capacitor phase converter must have some means of switching a large group of capacitors in and out during motor starting. Below is a typical unit uses a potential-type motor starting relay (pirated from a single-phase motor) to regulate the larger start capacitor, while a smaller (in value) capacitor provides continuous power to run the motor. The potential relay removes the start capacitor from the circuit as the motor speed increase, and the motor operates. [Circuit diagram source: gwm4-3phase.com]

Automotive 12V to +-20V Converter Circuit (for Audio Amplifier)

2011-04-13T07:55:00.000+07:00

The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers. In fact the max audio power x speaker (with 4 ohm impedance) using 12V is (Vsupply+ - Vsupply-)^2/(8*impedance) 12^2/32 = 4.5Watts per channel. This is the figure of the circuit diagram;

The transformer must be designed to reduce skin effect, it can be done using several insulated magnet wire single wires soldered together but conducting separately. The regulation is done both by the transformer turn ratio and varying the duty cycle. In my case i used 5+5 , 10+10 turns obtaining a step up ratio of 2 (12->24) and down regulating the voltage to 20 via duty cycle dynamic adjust performed by the PWM controller TL494. The step-up ratio has to be a little higher to overcome diode losses, winding resistance and so on and input voltage drop due to wire resistance from battery to converter. The output capacitors are 4700uF 25V, not very big, since at high frequency the voltage ripple is most due to internal cap ESR fortunately general purpose lytics have enough low esr for a small ripple (some tens of millivolts). Also at high duty cycle they are feed almost with pure DC, giving small ripple. This supply given me up to 85% efficiency (sometimes even 90% at some loads) with an input of 12V because i observed all these tricks to keep it functional and efficient. An o-scope would be useful, to watch the ripple and gate signals (watching for overshoots), but if you follow these guidelines you will avoid these problems.

Video Distributor Amplifier Circuit

2011-03-19T02:03:00.000+07:00

This circuit is design for useful to amplify and distribute video signals with low noise and without losses. The CA3100 is a fast op amp designed to amplify video signals. Set the P1 to control the input signal level to have a clear picture on the TV set. This is the figure of the circuit;

Signal Conditioning Circuit for KMI 15/x Rotation Speed Sensor

2011-03-19T01:53:00.000+07:00

This is a design circuit for modulated current that is provided by the integrated rotational speed sensor KMI 15/x. This current signal must be converted to ground referenced voltage signal, matching the logic levels of the processing unit for digital signal processing. This signal conditioning can be done by using this circuit. This circuit is consists of protective elements to suppress line conducted interference and low pass filter in front of the comparator input. This is the figure of the circuit;

This circuit uses first-order RC low pass filter as signal filter. This circuit is made of C4 and R3 with cut off frequency of 10 kHz. This cut off frequency is used to achieve an optimum absorption of noise.

Auto Off 12V NiCad Battery Charger Circuit

2011-03-19T01:51:00.000+07:00

NiCad/NiCad battery charger circuit is still needed since some application demanding high current is still rely on NiCad type, since this type is still superior in term of high current output (low internal resistance) and low cost. This is the figure of the circuit;

This battery charger circuit is used to charge 12V NiCad battery at around 74 mA until battery is fully charged. This circuit need around 4 hours to fully recharge a totally empty/dead battery, depends on the battery capacity. This circuit is basically a current source with auto cut-off. The current regulation is done by maintaining a fix voltage across a 68R at the emitter of 2N2219 transistor. This voltage is stabilized by a 5.6V zener diode 1N752, which keep the voltage at 68R resistor at around 5V, giving a constant current of 74 mA. The auto-off feature work by monitoring the output voltage (before the 1N4001 diode) relative to ground, as this voltage increases in accordance with the battery voltage which is being charged. After the battery voltage reach the fully-charged level, the lower 1N752 zener diode will pass the current to activate the 2N222 transistor, which short the upper transistor’s base, turning off the charging process. To calibrate the shut off point, connect a 270 ohm / 2 Watt resistor across the charge terminal and adjust the pot until the charging terminal voltage show 15.5V level.

Signal Conditioning Circuit for KMI 15/x Rotation Speed Sensor

2011-03-17T11:05:00.000+07:00

To block negative interference pulses and protect the sensor and electronics against reverse polarity of the supply voltage, this circuit uses the series diode D1. The suppressor diode D2 is used to limit positive interference pulses. Fast negative and positive interference pulses are absorbed by the capacitor C2. To supply the sensor during short supply voltage breakdown because of negative pulses, the electrolytic capacitor C3 stores energy. [Circuit diagram source: Philips Semiconductors Application Note]

Scoring Game Circuit

2011-02-21T10:42:00.000+07:00

This is a design circuit for scoring game circuit that can be used for all occasions when a dice is needed. The circuit is based on a NE555 timer, a 74LS192 counter,a74LS247 decoder and a & segment LED display. The timer IC1 will produce the clock for the counter IC(IC2) whose frequency is determined by R1 and C2.When S2 is pressed the IC2 will count in up mode and when S3 is pressed the IC2 will count in down mode. This is the figure of the circuit;

The IC 3 will decode the count to display it on the seven segment LED display. That is about the working of the circuit. The circuit is designed strictly sticking on to the basics of counters and is a good one for beginners. There is nothing big deal. To play the game switch the power ON and press S1 to reset the counter. Now press S2 or S3 and release .The IC2 will hold the last count .Now press S4 to see the score on display. That’s your score. Now the second person can try. Each time one tries, he should press the S1 to reset the count and then press S2 or S3 and then S4 to see the score. Circuit can be powered from a 9V radio cell or a 9V regulated DC power supply .

Basic Unity Gain Buffer Circuit

2011-02-10T22:45:00.000+07:00

This is a circuit for basic unity gain buffer circuit. The circuit gives the highest input impedance of any operational amplifier circuit. Input impedance is equal to the differential input impedance multiplied by the open-loop gain, in parallel with common mode input impedance. Here’s the figure of the circuit;

The gain error of this circuit is equal to the reciprocal of the amplifier open-loop gain or to the common mode rejection, whichever is less. Input impedance is a misleading concept in a DC coupled unity-gain buffer. Bias current for the amplifier will be supplied by the source resistance and will cause an error at the amplifier input due to its voltage drop across the source resistance. Since this is the case, a low bias current amplifier such as the LH1026 should be chosen as a unity-gain buffer when working from high source resistances.

VOUT = VIN
R1 = RSOURCE

The cautions to be observed in applying this circuit are three, the amplifier must be compensated for unity gain operation, the output swing of the amplifier may be limited by the amplifier common mode range, and some amplifiers exhibit a latchup mode when the amplifier common mode range is exceeded. The LM107 may be used in this circuit with none of these problems or, for faster operation, the LM102 may be chosen. [Circuit diagram source: National Semiconductor Application Notes]

AC Ohmmeter - ESR Meter Circuit

2011-02-10T22:42:00.000+07:00

The ESR Meter is basically an AC Ohmmeter with special scales and protective circuitry. It provides a continuous reading of series resistance in electrolytic capacitors. It operates at 100 kHz to keep the capacitive reactance factor near zero. Here’s the figure of the one design circuit for ESR meter circuit;

The ESR meter uses 8 operational amplifiers. An op-amp is an idealized basic amplifier with two inputs. The non-inverting input (+) has an in-phase relationship with the op-amp output, and the inverting input (-) an out-of-phase relationship. Op-amps are usually used with negative feedback and reach a stable operating condition when their two inputs are equal in voltage. Op-amps IA & 1B form a regenerative 100 kHz oscillator circuit. Capacitor C1 is the basic timing capacitor and RI is selected to set frequency. Diodes D2 & D3 clip the bottom and top of the output waveform so that the output level and frequency are resistant to battery voltage changes.

The oscillator output of op-amp 1B drives 10-ohm source resistor R8F. The test-capacitor, thru the test leads, couples this 100 kHz signal to 10-ohm load resistor R9F. The amount of voltage developed here is indicative of the capacitors ESR value. (The 10-ohm resistors determine the basic meter scaling.) Capacitor C3 blocks any DC voltage present on the test-capacitor. Diodes D4 & D5 protect the ESR Meter from any initial charging current to C3. Resistor R7 discharges C3 after test. A DC operating bias of 0.55 V is established by diode D1 for the oscillator stage and for all subsequent stages, which are DC coupled and operated class A. DC bias from D1 and ESR signal from R9F are combined at the input of op-amp 1D. Both voltages are amplified by 1D, 1C, & 2A. Each of these three stages has an amplification factor of about 2.8 due to the ratio of output-voltage to feed back voltage at the (-) input, which is determined -by feedback resistors R13F & R14F, etc.

Air Ionizer Circuit

2011-02-07T19:39:00.000+07:00

When in atmosphere exists accumulation of negative ions, it has been proved medical, that the human organism reacts favorably. Opposite happens when exists accumulation of positive ions. The lack of negative ions is the main cause for a lot of pathological abnormalities in our organism. Also it can '' clean '' the atmosphere of room from the tobacco of cigarette and the industrial pollution, as dust and exhaust etc, one and the negative ions overlay above in positive the pollutants and the '' neutralizes ''. This is the figure of the circuit;

It has been observed in periods of powerful storms, when '' they fall '' a lot of lightning, in atmosphere it exists the same sense, one and exists production of negative ions, in enormous quantities. The production of negative ions for us him it makes the above circuit, that is not nothing other than a multiplier of voltage. Thus 230V AC are changed in DC and they are multiplied in + 6500V roughly and via means of R13, they lead in contacts A-b-c-d-e, that is steel spikes (needles of length roughly 3-5cm). The high voltage that exists in the end of spikes, creates continuous flow of negative ions, the phenomenon that it creates and a very lightly blue radiation in their end. Even if the voltage, is high it does not create problem of electrocution (because is small current), but GOOD THEY IS WE DO NOT LEAN IN NO POINT of CIRCUIT, LONG AS THAT WORKS, BUT EVEN LITTLE TIME INTERVAL THAT THIS IS EXCEPT OPERATION, BECAUSE LIKELY THEY IS CHARGE STILL the CAPACITORS. If the circuit is manufactured and try then it will be supposed insulate are well, opened five holes in his side and from there behind are placed the spikes, WITHOUT UNDERHUNG FROM the HOLES.

Telephone Line Monitor Circuit

2011-02-07T05:42:00.000+07:00

This is a circuit that will find application in the case where you have a lot of telephones installed on a telephone line and would want to know if somebody of them is open. Thus you will not be off any discussion. Simultaneously it can cut the certain sound from stereo amplifier that are in high volume, the sound of some television or turn on some light the night when it ring the telephone and needs him you raise. Here’s the figure of the circuit;

Exists a pair of free contacts of RL1 that connects to the J2, which you can use connecting there any appliance you want. The telephone line connected in the J1, with what polarity you wants. When the telephone is closed then the line voltage is roughly, 48-50Vdc. This voltage turn on the photo diode and this, the transistor of IC1, which it simultaneously isolates, the circuit from the telephone line. The photo transistor in IC1 are now in situation ON, the input of IC2A are LOW [L] and output HIGH [H]. Ignoring for little the circuit of delay D6, R4, R5, C1, the IC2B input, are also this HIGH hence the output are LOW, transistor Q1 are OFF and the RL1 are deactivate. When the telephone earphone is raised, then the telephone voltage line fall in 6-10Vdc.

All the previous situation is reversed also the RL1, turn on. The telephones that use for dial choice, disk or pulse system, can they open and close the RL1 at the duration of choice. With delay network, that exist between in gates IC2A and in the IC2B, we delay the situation changes in the input of IC2B, ensuring thus stability in the operation of RL1. If the R4=100K then the RL1 is activated when the telephone ring or when the earphone is raised. On the contrary if the R4=1M, then the RL1 is activated only when the earphone is raised. The circuit supply becomes with a simple regulation circuit, in + 12V.

Part:

R1-2=36Kohm
R3=100Kohm
R4=100Kohm or 1Mohm
R5=2.2Mohm
R6=3.3Kohm
R7=1Kohm
D1....4=1N4002
D5=1N5252 [24V 0.5W Zener]
D6-7=1N4148
D8....11=1N4002
D12=Red Led 3 or 5mm
RL1=12Vdc 2X2 relay
J1-4=2pin connector 2.54mm step
J2=6pin connector 5mm step
J3=2pin connector 5mm step
F1=Fuse 500mA [5x20mm]
C1=100 or 220nF 100V MKT
C2=1000uF 25V
C3-4=100nF 100V
C5=4.7uF 16V
IC1=4N25 opto coupler
IC2=4011B
IC3=7812 [1A]
Q1=BD139 or BD679
T1=12Vac 500ma tranformer for pcb

Light Controlled Bistable Circuit

2011-02-02T19:55:00.000+07:00

This circuit is design that can control AC loads such as Lights, Fans etc through the remote handset of TV. The circuit uses the popular timer IC 555 in the Bistable mode. Here’s the figure of the circuit;

In this circuit, the Bistable mode output IC555 keeps two states, either low or high. When a negative pulse is applied to the trigger pin 2 of 555, the output turns high and remains as such in the latched state. If a positive pulse is applied to the Threshold pin 6, its output turns low and remains as such. This property is used to control the AC load. The negative and positive pulses are given to the trigger and threshold pins of 555 through the light activated phototransistors T1 and T2. The collector of T2 is connected to the trigger pin 2 through diode D1. Similarly the emitter of T2 is connected to the threshold pin 6 through diode D2. When the IR beam of remote is focused momentarily to T2, it conducts and takes the trigger pin 2 to ground potential. This triggers IC1 and its output goes high. T3 then conducts and relay turns on. Load connected to the NO contacts of the relay gets electrical continuity and turns on. When the IR beam is focused on T1, Current passes from its emitter into the threshold pin6 and the output of IC1 turns low and the relay de-energize to switch off the load.

555 IC’s Hysteresis for Dark Activated Relay Circuit

2011-02-02T19:51:00.000+07:00

This is a circuit that can be used for dark activated means the relay will be activated when the light intensity fall below a certain threshold. Without hysteresis, the relay will be activated and deactivated if the sensed brightness fall under or rise above a single point of darkness level. With hysteresis, the darkness level for activating and deactivating the relay will be different, and this solve the relay oscillation problem when the light intensity is swinging up and down around a single point of no hysteresis activation level. Here’s the figure of the circuit;

We can employ the hysteresis of a 555 IC to improve the sensing of a drop in light, since the internal 555 circuit has 1/3 and 2/3 supply voltage thresholds. We have to use a LDR or CDS cell with out 2 to 8 k resistance at desired light level. At the dark, the resistance of the LDR will rise and activate the relay if the voltage at pin 2 reach 2/3 of supply voltage (8V). After the relay is activated, more light is needed to make the LDR decrease its resistance until the voltage at pin 2 falls below 1/3 supply voltage (4V).

How to build Ultrasonic Radar

2011-01-30T18:27:00.000+07:00

It is very interesting project with many practical applications in security and alarm systems for homes, shops and cars. It consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. This is a one design circuit for the ultrasonic radar circuit. Here’s the figure of the circuit;

As it has already been stated the circuit consists of an ultrasonic transmitter and a receiver both of which work at the same frequency. They use ultrasonic piezoelectric transducers as output and input devices respectively and their frequency of operation is determined by the particular devices in use. The transmitter is built around two NAND gates of the four found in IC3 which are used here wired as inverters and in the particular circuit they form a multi vibrator the output of which drives the transducer. The trimmer P2 adjusts the output frequency of the transmitter and for greater efficiency it should be made the same as the frequency of resonance of the transducers in use. The receiver similarly uses a transducer to receive the signals that are reflected back to it the output of which is amplified by the transistor TR3, and IC1 which is a 741 op-amp. The output of IC1 is taken to the non inverting input of IC2 the amplification factor of which is adjusted by means of P1. The circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic emission the signal that is reflected back to the receiver becomes distorted and the circuit is thrown out of balance. The output of IC2 changes abruptly and the Schmitt trigger circuit which is built around the remaining two gates in IC3 is triggered. This drives the output transistors TR1,2 which in turn give a signal to the alarm system or if there is a relay connected to the circuit, in series with the collector of TR1, it becomes activated. The circuit works from 9-12 VDC and can be used with batteries or a power supply.

Digital Radar Speedometer Circuit

2011-01-30T18:24:00.000+07:00

This circuit is use to Digital Radar Speedometer. It allows us to evaluate the speed of any object moving, especially cars and other vehicles. The speed is calculated in kilometers per hour (KPH). Its display has three digits. This radar works with the laser reflection. It sends laser radiation to the object and this object reflects the laser radiation to the radar. To evaluate the speed of a vehicle, we must be in front of it. In other words, the vehicle must come in our direction. Here’s the figure of the circuit;

The laser LED can send a spot of light to a distance of 90 m (295 ft). It's very important that the distance range of the laser LED is 90 m, if not, the speed will not be calculated properly. The laser diode, which receives the light signal by the laser LED, must be able to detect the light which is same color as that emitted by the laser LED. The laser diode and the laser LED must be placed one beside the other. They are protected by a tinted pane. They must be placed at the front of the radar and point the outside. The radar is powered by a 9V battery and it has a SPST switch to control its power state.

The display, or the speed indicator, is placed at the rear of the radar, just on the right of the overload LED indicator. All the logic components of the circuit must be of the 74AS series and TTL type. Because they have short time of response (less than 1.7 ns) and have high frequency supports (more than 200 MHz). The radar can evaluate the speed of an object moving between 0 to 999 km/h. After this speed, the overload LED indicator will turn on and the "999" will still displayed. The radar displays the speed during 3 seconds, after this time, it displays "zero" (0).

PWM Power Controller Circuit

2011-01-27T21:02:00.000+07:00

This is a circuit that can uses a 555 timer to generate a saw tooth voltage waveform across a capacitor, then compares that signal against a steady voltage provided by a potentiometer, using an op-amp as a comparator. The comparison of these two voltage signals produces a square-wave output from the op-amp, varying in duty cycle according to the potentiometer's position. This is the figure of the circuit;

This variable duty cycle signal then drives the base of a power transistor, switching current and and off through the load. The 555's oscillation frequency is much higher than the lamp filament's ability to thermally cycle (heat and cool), so any variation in duty cycle, or pulse width, has the effect of controlling the total power dissipated by the load over time. Controlling electrical power through a load by means of quickly switching it on and off, and varying the "on" time, is known as pulse-width modulation, or PWM. It is a very efficient means of controlling electrical power because the controlling element (the power transistor) dissipates comparatively little power in switching on and off, especially if compared to the wasted power dissipated of a rheostat in a similar situation. When the transistor is in cutoff, its power dissipation is zero because there is no current through it. When the transistor is saturated, its dissipation is very low because there is little voltage dropped between collector and emitter while it is conducting current.

PWM is a concept easier understood through experimentation than reading. It would be nice to view the capacitor voltage, potentiometer voltage, and op-amp output waveforms all on one (triple-trace) oscilloscope to see how they relate to one another, and to the load power. However, most of us have no access to a triple-trace oscilloscope, much less any oscilloscope at all, so an alternative method is to slow the 555 oscillator down enough that the three voltages may be compared with a simple DC voltmeter. Replace the 0.1 µF capacitor with one that is 100 µF or larger. This will slow the oscillation frequency down by a factor of at least a thousand, enabling you to measure the capacitor voltage slowly rise over time, and the op-amp output transition from "high" to "low" when the capacitor voltage becomes greater than the potentiometer voltage. With such a slow oscillation frequency, the load power will not be proportioned as before. Rather, the lamp will turn on and off at regular intervals. Feel free to experiment with other capacitor or resistor values to speed up the oscillations enough so the lamp never fully turns on or off, but is "throttled" by quick on-and-off pulsing of the transistor.

555 Ramp Generator Circuit

2011-01-27T20:59:00.000+07:00

This is a design circuit that can using a 555 timer IC as an astable multi vibrator, or oscillator. This time, however, we will compare its operation in two different capacitor-charging modes: traditional RC and constant-current. This is the figure of the circuit;

Connecting test point #1 (TP1) to test point #3 (TP3) using a jumper wire. This allows the capacitor to charge through a 47 kΩ resistor. When the capacitor has reached 2/3 supply voltage, the 555 timer switches to "discharge" mode and discharges the capacitor to a level of 1/3 supply voltage almost immediately. The charging cycle begins again at this point. Measure voltage directly across the capacitor with a voltmeter (a digital voltmeter is preferred), and note the rate of capacitor charging over time. It should rise quickly at first, then taper off as it builds up to 2/3 supply voltage, just as you would expect from an RC charging circuit.

Remove the jumper wire from TP3, and re-connect it to TP2. This allows the capacitor to be charged through the controlled-current leg of a current mirror circuit formed by the two PNP transistors. Measure voltage directly across the capacitor again, noting the difference in charging rate over time as compared to the last circuit configuration.

Battery Level Indicator Circuit

2011-01-26T15:38:00.000+07:00

This is the design of battery level indicator circuit. This circuit is designed for 9V battery operation, as this circuit will start dimming below 7V and will be completely turned off at 6V. If you want the LED indicator not to dimming but just abruptly turn off at below 6V, then you can remove R3, and change R1 to 330k. This is the figure of the circuit;

[Circuit diagram source: National Semiconductor Application Note]

Audio Power Meter: Shows Your Audio Amplifier’s Actual Output Power

2011-01-26T15:36:00.000+07:00

This is a circuit that can be used to measure the actual output power of your amplifier. You can put this circuit in a box as a measurement instrument, or you can integrate it inside your power amplifier to get real power display. This is the figure of the circuit;

This circuit would be a handy instrument for audio engineer, for field testing and checking of sound system installations. Because the scale is logarithmic, you can measure wide range of audio output with only ten scales. Look at the pin 5 of the LM3915, you can see that the input is not rectified. The negative swing will present at this input pin, but it harmless because the current is limited by R1, and the LM3915 will respond to positive cycle only.

The absence of peak detector or average detector will give the circuit a fast reading of instantenous power, and this gives us insight of both average and peak condition. For more readable peak or average measurement, you can use peak or average detector circuit. [Circuit diagram source: National Semiconductor Applicataion Notes]

Active Power Factor Correction Circuit

2011-01-26T15:34:00.000+07:00

Active power factor correction stabilize the electrical demand of a device to give the best power factor characteristic of many types of loads. To meet power factor regulation, a low cost solution should be designed. In many application, the need of high DC voltage is usually implemented by a direct rectification of the AC line followed by bulk capacitor filtering. This is the figure the circuit;

This capacitor filtering introduce current spike that distort the power line sine waveform, and this introduce a poor power factor, resulting in an apparent input power that is much higher than the real power. This can be solved by inserting a pre-regulation between the rectifier and the bulk capacitor. We call this pre-regulator circuit as power factor correction circuit. This power factor controller is a low–cost system solution for boost mode follower. that meets IEC1000–3–2 standard. This power factor correction circuit includes an inrush current detection, protection against over current, overvoltage and under voltage. Follower boost mode for system cost reduction – smaller inductor and MOSFET can be used. [Circuit diagram source: ON Semiconductor Application Notes]

Ultrasonic Measurement Circuit Using Electrostatic Transducer

2011-01-02T10:56:00.000+07:00

This is a design circuit for an electrostatic transducer for ultrasonic measurement circuit. This circuit uses the LM1812 ultrasonic transceiver. Transducer x1 and LM1812 will transmit a burst of oscillations. Then the return echo is listened by using X1. The LM1812 detector will generate a pulse of the same width as the original burst when the X1 receive an echo of sufficient amplitude. If the return echo is early, it’s mean the object is near. This is the figure of the circuit;

If the parts and values shown are used, this circuit has a range of about 4 inches to 30 feet. The X1 has a 500-pF capacitance that resonate with the L6 at 50 to 60kHz. The L1 is tuned to this frequency by watching for maximum echo sensitivity with a scope at pin 1. [Circuit diagram source: National Semiconductor Linear Application]

Vpp Programming Supplies Features High Repetition Rate

2010-12-24T02:12:00.000+07:00

Programming old EPROM devices needs high voltage, and this is a circuit of high repetition rate Vpp programming supplies. This circuit is used for memory programming that need higher repetition rate. This circuit produces the Vpp continuously by the switching regulator that runs continuously. To preclude any possibility of inadvertent Vpp output, the switching regulator mus t be turned of by driving the Vpp lock line. This is the figure of the circuit;

The LT1072 loop comes on if the Vpp lock goes low, stabilizing at about 17V. This circuit has a clean rise time because of the two pole compensation. The LT1004 reference is biased by the 74C04 when the Vpp command line is low. The A2 and A1 give a scaled output and the LT1004 clamps at 1.23V. To control loop slewing, this circuit uses 680pF that also erase the overshoots. [Circuit diagram source: Linear Technology Application Note]

The Time Delay Circuit

2010-12-24T02:11:00.000+07:00

This is a simple circuit for the time delay circuit. This circuit is based on transistor as controller the circuit. This is the figure of the circuit;

The length of time the circuit stays on for depends on how long it takes for the stored electrical current to leak back into the circuit, keeping the transistor (and thus the entire circuit) energized. We have a resistor that is limiting the rate at which the capacitor can discharge. If we increase the value of that resistor, it will take the capacitor longer to discharge and so the cold starting circuit will stay energized for longer. Likewise, if we decrease the value of the resistor, the capacitor will discharge more quickly, and the circuit will operate for a shorter period of time.

TC9400 VFC for PLL FM Demodulation

2010-12-24T02:09:00.000+07:00

FM demodulation can be done with phase locked loop (PLL), and this method is common in high-end communication system. This system uses TC9400 that has high linearity. Using TC9400, the performance of phase-locked loop will increases greatly. That will give very precise tracking of Vout with respect to Fin. This is the figure of the block diagram;

The operation principle is very simple, since the feedback system force the V/F converter (VFC) to follow the FIN by manipulating the control input of VFC, as the result, the control input of VFC will follow the variation of FIN. This control signal is then tapped for the output of this circuit. [Block diagram source: Microchip Application note]

Self-Writing LED Display Sign Controller

2010-12-24T02:08:00.000+07:00

This is a design for a circuit of self-writing LED display sign controller. This circuit consist of eight power shift register which are installed in cascade. The shift registers are used to turn on a string of 64 lamps or LEDs sequentially. This is the figure of the circuit;

When the shift register clock (SRCK) is clocked, the register is clocked, so that the display is update after each bit of data is shifted in. The LEDs strobe on from left to right and until the LEDs strobe off in the same manner because of the serial input data (SER IN) is held alternately high and low for any period greater than 64 clocks. The display sign is dynamic and attractive because the LEDs arranged sequentially as in written message.

This circuit uses LM556 timer to generate the clocks and requires only one IC in addition to the shift register. To blanking or blinking the LEDs, this circuit uses the output enable. [Circuit diagram source: Texas Instruments Application Report]

LM1893 for Power Line Modem Circuit

2010-12-24T02:05:00.000+07:00

This design circuit is shows an LM1893 power line modem circuit. This circuit is used to transfer information between remote locations by using the power mains. This circuit uses LM1893 that is used as a power line interface for half-duplex (bi-directional) communication of serial bit stream of virtually any coding. This is the figure of the circuit;

To give maximum range, impulse noise filter and a PLL-based demodulator are combined in reception. In transmission, a sinusoidal carrier is impressed and FSK modulated on most any power line via rugged on-chip driver. Besides LM1893, this circuit also uses a COPS controller and discrete components. [Circuit diagram source: National Semiconductor's Application Note]

Electronic Metronome Circuit

2010-12-24T02:04:00.000+07:00

Metronome is very important tool if you studying music playing. There are mechanical metronome device in the past, but today, electronic metronome is much more popular since it can be very simple, compact/small, reliable, and also has the most interesting feature: cheap. And this is the figure of the circuit;

Parts:
·    C1 1 uF 63V Polyester Capacitor
·    C2 10nF 63V Polyester Capacitor
·    C3 47 uF 25V Electrolytic Capacitor
·    R1 10K 1/2W Trimmer Cermet
·    R2 10K 1/4W Resistor
·    R3 330K 1/4W Resistor
·    R4 50K 1/2W Trimmer Cermet
·    R5 100K 1/4W Resistor
·    R6,R7 1K 1/4W Resistor
·    P1 100K Linear Potentiometer
·    SW1 SPST Switch (Ganged with P1)
·    SPK 8 Ohm 40mm. Loudspeaker
·    B1 12V Battery (MN21, GP23A or VR22 type)
·    IC1 NE555 General purpose timer IC
·    Q1,Q2 BC560 45V 100mA Low noise High gain PNP Transistors
·    Q3 ZTX753 100V 2A PNP Transistor

A variable current source is built around Q1 and Q2, this provides linear scale that can be directly mapped to the potentiometer position. Transistor Q3 is employed to amplify the signal to get louder click sound, similar to clockwork metronomes. To obtain more output power and more compact package, a 12V micro battery was used. Don’t worry if you can’t get the battery since it works also for 9V battery. Rotate P1 fully towards R2, then set R1 to obtain 40 beats per minute (compare with another metronome). Rotate P1 fully towards R3, then set R4 to obtain 208 beats per minute.

Finally mark the entire scale with the common metronome steps as following:
40 – 42 – 44 – 46 – 48 – 50 – 52 – 54 – 58 – 60 – 63 – 66 – 69 – 72 – 76 – 80 – 84 – 88 – 92 – 96 – 100 – 104 – 108 – 112 – 116 – 120 – 126 – 132 – 138 – 144 – 152 – 160 – 168 – 176 – 184 – 192 – 200 – 208.

Analog Signal Transmission Over Telephone Lines

2010-12-24T02:02:00.000+07:00

This is a circuit for telephone line is designed to carry audio signal, which is an alternating current in nature. To transmit measurement signal, which has very low frequency or DC signal, we have to convert the signal into AC with acceptable frequency range for telephone line transmission. This is the figure of the block diagram circuit;

For transmitting analog data over telephone lines, its ideal to use the TC9400′s square-wave output. Since the square wave takes up less frequency spectrum a square wave is actually preferred over a pulse waveform for data transmission. By use of low pass filters, the square wave’s spectrum can be further reduced. The TC9400 converts the frequency signal back into a voltage output linearly proportional to the original input voltage at the end of the telephone line. [Block diagram source: Microchip Application Note]

Analog Signal Transmission Circuit Through DC Supply Line

2010-12-24T02:01:00.000+07:00

If the sensor system need an active supply, we can use only a single pair of cable to carry both the power supply and the output signal. Not only simplify the wiring, converting analog voltage level to frequency modulated pulse improve the noise immunity as well. This is the figure of the circuit;

The diode is employed to prevent the capacitor voltage to be discharged when the transistor is grounding the supply voltage source to send a zero pulse. If the sensor or input system need a supply, we can tap the power from the 1uF capacitor, as long as it need only small current. [Circuit diagrams source: Microchip Application Note]

NPN Transistor Darlington Configuration

2010-11-22T04:03:00.000+07:00

In the Darlington configuration, this emitter follower has a pair of transistors. The emitter current of one transistor becomes the base current of the second in this arrangement. The Darlington configuration acts like one transistor with a beta which is the product of the betas of the two transistors. This is the figure of the circuit;

Where high output currents are needed, they can be used. The Darlington configuration has a quite high input impedance. The resistor is commonly tied between the emitters to increase the speed switching because switching of the second transistor may be slow. Darlington pairs are available as single packages with resistor included.

Cuckoo Sound Simulator (Synthesizer/Generator) Circuit

2010-11-18T06:02:00.000+07:00

A two tone effect very much alike cuckoo sound is generated by this circuit. We can use this circuit for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker. Used as a sound effect generator, it can be connected to external amplifier, tape recorder, etc. The built-in audio amplifier and loudspeaker may be omitted and the output taken from C8 and ground in this case. There are two options: when SW1 is left open, we can use free running and when SW1 is closed we can use one-shot. A two-tone cuckoo sound will be generated each time P1 pushbutton is pressed in this case. This is the figure of the circuit;

IC1 is wired as a squarewave generator and two tones of cuckoo sound is produced by this IC. The frequency of the higher one (667Hz) is set by means of Trimmer R2. A further trimmer (R22) is added to IC1 timing components via D6, and the lower tone (545Hz) is generated when IC2D output goes low. The the squarewave output of IC1 is converted to a quasi-sinusoidal waveform by R3, R4, C3 and C4, then mixed with the white noise generated by Q1, R6 to imitate closely the cuckoo sound.Q2 has two purposes: it mixes the two incoming signals and gates the resulting tone, shaping its attack and decay behavior by means of the parts wired around its Emitter.

R15 is the volume control and IC4 is the audio power amplifier driving the speaker. The clock generator IC2A driving the decade counter IC3 provides the various sound and pause timings for the circuit. Some output pins of this IC are gated by IC2C, IC2D and related components to drive appropriately the sound generator and the sound gate. The circuit operates in the free-running mode and a cuckoo sound is generated continuously when SW1 is left open. the circuit generates two tones then stops, because a high state appears at the last output pin (#11) of the decade counter IC: therefore the count is inhibited by means of D1 feeding pin #13 when SW1 is closed. When P1 is pressed, the circuit is reset by a positive pulse at pin #15 of IC3. If the two tones frequencies are set precisely, the best result will be obtained. i.e. 667Hz for the first tone and 545Hz for the second (called Minor Third in musical terms). If available, a digital frequency would be the best tool to set up R2 and R22. You can use a musical instrument such as piano or guitar. Here’s the step to tuning-up the notes by musical instrument: First, we have to disconnect R22 from D6 diode temporarily then connect the digital frequency counter to pin 3 od IC1. To read 667Hz on the display, adjust R2 in order then connect R22 to negative ground and adjust it to read 545 Hz on the display and finally reconnect R22-D6.

Then, steps to tuning by ear: First, disconnect R22 from D6 anode temporarily. Disconnect C8 from Q2 Collector and connect it to R4, C4 and C5 junction. After that, adjust R2 in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This reference note will be the E written on the stave in the fourth space when using the treble clef. Then, Connect R22 to negative ground and adjust it in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This second reference note will be the C-sharp written on the stave in the third space when using the treble clef. Finally reconnect R22-D6 and C8-Q2 connections. For your note, the master clock can be adjusted by means of R18. The percentage of hiss and sound in the mixing circuit, setting the tone character, can be varied changing R8 and R7 values respectively. Any kind of dc voltage supply in the 12 – 15V range can be used, but please note that supply voltages below 12V will prevent operation of the white noise generator and an amusing application of this circuit is to use a photo-resistor in place of P1, then placing the unit near the flashing lamps of your Christmas tree. A sweet cuckoo sound will be heard each time the lamp chosen will illuminate.

Sound to Dancing Lights Converter Circuit

2010-09-29T19:22:00.000+07:00

This is a design circuit for converting an audio signal (such as one that comes from the speaker terminals of a CD player). The circuit basically consists of a buffer/amplifier stage and three filter circuits: a high-pass filter, a mid-pass filter, and a low-pass filter. The output of each filter circuit drives a light-emitting diode of different color. This is the figure of the circuit;

The input signal is fed to the buffer stage through C1. The values of RF and RV1 should be chosen so that the buffer is able to drive the three filters attached to its output. The low-frequency, mid-frequency, and high-frequency components of the input signal are only allowed to pass through the low-pass filter (bottom filter), the mid-pass filter (middle filter), and the high-pass filter (topmost filter), respectively, thus separating them from each other. Changes in the output of a filter cause its corresponding output LED to turn on and off. In effect, feeding a continuous audio signal to the input of this circuit causes the LED's to 'dance'.

Negative/Positive DC Voltage Power Supply Circuit

2010-09-29T19:11:00.000+07:00

This is a design circuit for a power supply circuit that provides regulated +12V and -12V outputs. The diode bridge formed by D1, D2, D3, and D4 performs the rectification needed to convert the transformer's AC current into a DC current. By using the center tap of the transformer as ground, DC voltages of opposite polarities with respect to this ground can be generated from the transformer's AC current. This is the figure of the circuit;

During the 'positive' cycle, the transformer current travels through D1, charges up C1, goes to ground, charges up C3, travels through D3 and then returns to the opposite tap of the transformer. Note that the C1 voltage built up is positive with respect to ground while that of C3 is negative. During this cycle, D2 and D4 are 'off'.

During the 'negative' cycle, the transformer current travels through D2, charges up C1, goes to ground, charges up C3, travels through D4 and then returns to the opposite tap of the transformer. Note that this path also gives C1 and C3 a positive and a negative voltage, respectively. During this cycle, D1 and D3 are 'off'. The C1 and C3 voltages are then fed into the 7812 (+12V regulator) and 7912 (-12V regulator) IC's to come up with regulated +12V and -12V outputs, respectively.

Multi Wire Cable Tester Circuit

2010-08-26T19:52:00.000+07:00

This is a circuit for multi wire cable tester with a separate LED for each wire. Will show open circuits, short circuits, reversals, earth faults, continuity and all with four IC's. Designed initially for my intercom, but can be used with alarm wiring, CAT 5 cables and more. This is the figure of the circuit;

The circuit comprises transmitter and receiver, the cable under test linking the two. The transmitter is nothing more than a "LED chaser" the 4011 IC is wired as astable and clocks a 4017 decade counter divider. The 4017 is arranged so that on the 9th pulse, the count is reset. Each LED will light sequentially from LED 1 to LED 8 then back to LED 1 etc. As the 4017 has limited driving capabilities, then each output is buffered by a 4050. This provides sufficient current boost for long cables and the transmitter and receiver LED's. The receiver is simply 8 LED's with a common wire.

Heating Circuit System for Thermostat

2010-08-26T19:50:00.000+07:00

This is a circuit for heating in the thermostat that is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. The output from the Relay contact must be connected to the boiler's start-stop control input. This is the figure of the circuit;

When Q1 Base to ground voltage is less than half voltage supply (set by R7 & R9), a voltage is generated across R8 and the driver transistors Q2 & Q3 switch-on the Relay. When Q1 Base to ground voltage is more than half voltage supply, caused when one of the n.t.c. Thermistors lowers its value due to an increase in temperature, no voltage appears across R8 and the Relay is off. C3 allows a clean switching of the Relay. P1 acts as main temperature control.

Part;
P1 1K Linear Potentiometer
R1 10R 1/4W Resistor
R2 1K 1/4W Resistor
R3 3K3 @ 20°C n.t.c. Thermistor (see Notes)
R4 2K2 @ 20°C n.t.c. Thermistor (see Notes)
R5 10K 1/2W Trimmer Cermet
R6 3K3 1/4W Resistor
R7,R9 4K7 1/4W Resistors
R8 470K 1/4W Resistor
R10 10K 1/4W Resistor
C1,C2 470µF 25V Electrolytic Capacitors
C3 1µF 63V Electrolytic Capacitor
D1,D2,D4 1N4002 100V 1A Diodes
D3 LED Red 3 or 5mm.
Q1 BC557 45V 100mA PNP Transistor
Q2 BC547 45V 100mA NPN Transistor
Q3 BC337 45V 800mA NPN Transistor
RL1 Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm
J1 Two ways output socket
SW1 SPST Mains Switch
T1 220V Primary, 12 + 12V Secondary 3VA Mains transformer
PL1 Male Mains plug & cable

73 MHz Hallogene Lamp Radio Controlled Circuit

2010-08-26T19:46:00.000+07:00

This is a circuit for hallogene lamp radio control. This circuit has purpose of it is to control the power state of a hallogene lamp by a remote control. When we press the push button of the remote control, the power state of the lamp will be changed, so, if the lamp was turned on, it will turned off and if it was turned on, it will turned off. If we press to the button another time, the same action will be occure. When the button is pressed, a LED indicator lights on the remote control. This is the figure of the circuit;

The system is consisted by two separate circuit. One is the remote control, or the emmetor. The other is the receptor, or the hallogene lamp controller. We plug the input of the lamp controller circuit to the 120VAC source of the sector to supply it. The lamp must be pluged to the output of the circuit to be supplied and controlled. The controller circuit has also an antenna to receive the signal of the remote control. The remote control has also an antenna to transmit the signal to the controller circuit and have to be powered by a 9V battery. Two things important for my circuit are not mentioned in the schematic. There are about the two logic component. The first one is the Schmitt trigger NOT gate (74LS14). Its Vcc pin must be connected to the output of the +5V regulator (7805). And its GND pin must be connected to the ground of the circuit. The second one is the JK Flip-Flop (74LS76). Its Vcc pin must be connected to the output of the +5V regulator (7805). And its GND pin must be connected to the ground of the circuit.

Network Lead Tester Circuit

2010-08-14T23:07:00.000+07:00

This is a circuit for confirming the continuity and correct wiring of computer network leads which have 8 wires, but it can be used to check any lead with up to 8 wires by using appropriate connectors. For example stereo audio leads with 5-pin DIN plugs can be checked by just using the first 5 LEDs. The tester is simple but it can save a great deal of time when making up leads and it is much cheaper than the more sophisticated alternatives. This is the figure of the circuit;

The tester works by connecting each wire to an output at one end and an LED at the other end. The outputs are switched on one at a time in sequence so that a correctly wired lead will make each LED light in turn. The 4017 IC counts up to 10 so there is a pause (for the 9th and 10th counts) before the LED sequence repeats. If the LEDs light up in the wrong sequence one (or both) of the connectors is wired wrongly. If an LED fails to light it indicates a broken connection. Please note that the RJ45 computer network plugs cannot normally be re-wired, instead they must be cut off and replaced.

Intercom Circuit Using LM390

2010-08-14T23:04:00.000+07:00

This is a circuit for an intercom is a is a stand-alone electronic communications system intended for limited or private dialogue. Below schematic shows the application circuit of LM390 on intercom. Gain control can be done by capacitively coupling a resistor (or FET) from pin 6 to ground. This is the figure of the circuit;

Cell Phone Battery Meter Circuit 3.6 Volt

2010-08-14T23:02:00.000+07:00

This is a circuit for charger that is is a similar circuit to the above and provides a 4 LED bar graph indicating the voltage of a common 3.6 volt Lithium – Ion recharable cell phone battery. The reference voltage is provided by a TL431 programmable voltage source which is set to 3.9 volts where the TL431 connects to the 1K resistor. The lower reference for the LED at pin 14 is set with the 5K adjustable resistor. This is the figure of the circuit;

The programmed voltage of the TL431 is worked out with a voltage divider (10K 5.6K). The adjustment terminal or junction of the two resistors is always 2.5 volts. So, if we use a 10K resistor from the adjustment terminal to ground, the resistor current will be 2.5/10000 = 250uA. This same current flows through the upper resistor (5.6K) and produces a voltage drop of .00025 * 5600 = 1.4 volts. So the shunt regulated output voltage at the cathode of the TL431 will be 2.5 + 1.4, or 3.9 volts.

Working out the LED voltages, there are three 390 ohm resistors in series with another adjustable (5K) resistor at the bottom. Assuming the bottom resistor is set to 2K ohms, the total resistance is 390+390+390+2000 = 3170 ohms. So, the resistor current is the reference voltage (3.9) divided by the total resistance, or about 3.9/ (390 + 390 + 390 + 2000) equals 1.23 mA. This gives us about .00123*2000= 2.46 volts for the bottom LED, and about .00123*390 = .48 volts for each step above the bottom. So, the LEDs should light at steps of 2.46, 2.94, 3.42, and 3.9. A fully charged cell phone battery is about 4.2 volts. You can adjust the 5.6K resistor to set the top voltage higher or lower, and adjust the lower 5K resistor to set the bottom LED for the lowest voltage. But you do need a 6 to 12 volt or greater battery to power the circuit.

Intercom Circuit

2010-08-02T15:42:00.002+07:00

This is a simple form circuit for a 2-station intercom using common 8R mini speakers. The “press-to-talk” switches should have a spring-return so the intercom can never be left ON. This is the figure of the circuit;

Power the speaker from a separate power supply is the secret to preventing instability (motor-boating) with a high gain circuit like this. An extra station (or two extra stations ) can be connected to this design.

DTMF Decoder Circuit For PC

2010-08-02T15:41:00.002+07:00

This is a design circuit for decoder circuit that can be use for DTMF circuit for PC. This is the figure of the circuit;

Our DTMF decoder can be powered from a 9V battery or from your parallel printer port. It can detect and display all 16 DTMF digits on your computer screen in real-time. The Window's program can be placed in the minimize mode and still detect tones while you use your computer to do other things like We are now in the process of adding an DTMF decoder which will interface to the sound card game port.

555 IC PWM Controller Circuit: Grounded and Ungrounded Load

2010-08-02T15:40:00.000+07:00

While keeping the oscillator frequency relatively stable, this 555 based PWM controller features almost 0% to 100% pulse width regulation using the 100k variable resistor. To give a frequency range from about 170Hz to 200Hz , the frequency is dependent on the 100k pot and 100n. This is the figure of the circuit;

You can see the charging and discharging of the 100n cap is done through output pin 3, and this provide a push-pull symmetric drive for easy pulse-width setting. You can see two versions, the left side for grounded load, and the right side for ungrounded load. The grounded one use pin 7 to drive the transistor, while the ungrounded one use the same push-pull output pin3, this difference is needed because wen need an inverted phase to provide consistent potentiometer scale on both version. [Circuit source: talkingelectronics.com]

9V Battery Voltage Monitor Circuit

2010-07-30T12:50:00.002+07:00

This is a circuit that can be use for monitoring the voltage of battery. This is the figure of the circuit;

Nine voltage batteries are used in a wide variety of electronic devices. But, you often don’t know when it is time to change the battery until the device stops operating. The hobby circuit below provides a visual indication when the battery needs to be replaced. It uses a neat IC from Linear Technology, which contains a very low power voltage reference and a voltage comparator. The circuit is designed to turn on a LED indicator light when the battery voltage drops below 7.2 volts. [Circuit schematic source: discovercircuits.com]

Intercom Circuit

2010-07-28T13:48:00.000+07:00

Backlight Driver for WLED Display Circuit

2010-07-13T06:44:00.000+07:00

This is a design circuit for WLED-display backlight driver circuit. This circuit can be used to power WLEDs by replacing the voltage-feedback network with a series current-sense resistor, R3, and the WLED strings. This circuit uses The TPS6108x that drive some series WLEDs in parallel for backlighting larger displays. This is the figure of the circuit;

The feedback of this circuit is The voltage across the current-sense resistor. This feedback provides regulation. This circuit uses 1.2-V feedback voltages. The power lost of this circuit because of R3 is Plost= Iwled*Iwled*R3 = 1.2V*Iwled. The TPS6108x converters is equipped with an SS pin that can provide variable soft startup for boosted voltage regulation applications. Beside that, The SS pin can be used to lower the FB-pin reference voltage and to reduce sense-resistor power loss in aWLED current-regulation application. The FB-pin reference voltage can be lowered by connecting a resistor, R1, from the SS pin to GND. WLED current can be calculated by following equation:

Iwled=(Iss*R1)/R3

Analog dimming is provided by A second resistor, R2, that is connected with the FET and Q1 in series connection and parallel connection with R1. Those connections will lower the regulated FB-pin voltage across the sense resistor.

[Schematic circuit source: Texas Instruments Application Note]

Zone Alarm 6 with Seven Segment Circuit

2010-06-24T09:54:00.000+07:00

This circuit is a circuit diagram of an alarm system which has 6 independent zones, timed 1 entry / exit zone, a 7-segment LED display. Suitable for small office or home environment, can also be adapted to use a combination lock or keypad to set and reset the alarm. Each zone Z1 to 6 have their own indicators. Switch S1 is a single pole, double throw switch. One position is set, the other is reset / unset. This is the figure of the circuit;

Switch S2 allows a “manual” test to test all zones and screens. Zone 1 has been independent and out of time. Zone 1 is a timed zone which must be used as a point of entry and exit from the building. Straight 2-6 zone is the zone, which will trigger the alarm without delay. Some RF immunity provided for long wiring run by the input capacitors, C1 – C6. Key switches, S1 acts as the Set and Reset / unset switches. For the best security to this type of metal with a key switch. All IC’s except IC6 is a type of CMOS buffered output, is denoted by the suffix “B”. Unbuffered CMOS IC that has a suffix beginning “U” and will not work in this series. IC6 is a 5 volt regulator provides power to the main CMOS IC’s.

In operation S2 is the switch can be set to “run” position. When keyswitch S1 is restarted, this is unset (off) state of alarm. In this condition the capacitor C8 will discharge through D9, R1 aand Z1 and capacitor C7 will be discharged through D8, R17 and S1. Would not relay RLY1 energy and all the CMOS IC and the display will not have power. When S1 is activated to regulate all CMOS IC’s receive a 5 Volt power. C11 will be a while charging and a low input signal applied to one half of U7A a CMOS4001B, dual input OR gate. U5A output would also lower (make sure all windows and doors closed zones 2-5) and the output of high U7A. U7A output is then inverted by U7B and again in February through R18 to the input latch circuit U7A maintain. U7B low output and so Q1 and relay RLY1 inactive and no alarm will sound.

Also, when S1 is set, slowly C8 charges through R13. C8 and R13 form out timer and allow time to clear the building. The delay is approximately 1.1 x the value of C8 (at UF), or about 52 seconds with the values shown. During the delay out of the zone Z1 can switch opened and closed without triggering an alarm. After the exit time expires, the C8 will be filled and one half of the 2 input AND gate, U5A will be high. Each opening of zone 2 to 6 will cause the alarm to trigger and relay will RLY1 energy. If an intruder tried to break-ins through zone 4 for example, the output of U1D countries will change from low to high. When this happens, the signal transmitted by the high U2C triple input OR gate CMOS4075 and sent to the input D2 in the BCD to Decimal CMOS4511 display drivers. D2 is a binary code for the four and the LED display will illuminate the figure 4. High output from U2C also forwarded to U5A, another triple input OR gate. Output of U5A is now sent through S2 to input from U7A. U7A and bistable latch formed U7B, changes in circumstances that cause the output to change U7A low, the output from U7B to be high and feedback through R18 to the input of U7A again. The circuit is now locked in a high state. High output U7B do two things. First, in Q1 switches and alarm relays RLY1. Both high output applied to the blanking U7B input from CMOS4511B through S2 and also to enable the pins attached. View now will continue to show triggered zone numbers, even if the zone is opened or closed switch again. This is a similar process for all other zones immediately.

Part:
R1, R4, R6, R7, R10, R11 = 100k
R2, R3, R5, R8, R9, R12 = 270R
R13 = 1M
R14 = 4k7
R15, R18 = 470k
R16 = 100R
R17 = 1K
R19 = 10K
C1, C2, C3, C4, C5, C6, C9, C11 = 100nF
C7, C8 = 47u
C10 = 100u
D7, D8, D9 = 1N4148
Q1 = 2N3904
RLY1 = Relay 12V Coil 500R
Z1, Z2, Z3, Z4, Z5, Z6 = Contact NC
S1 = SPDT
S2 = Degree DPDT
U1 = 4050B
U2, U5 = 4075B
U3 = 4511B
U4 = 4081B
U6 = 7805
U7 = 4001B
BZ1 = Buzzer

Fuzz Distortion Circuit with Wave Shaper

2010-06-24T09:52:00.000+07:00

This is the design circuit for guitar effect circuit. This is called as fuzz distortion effect. Based on the squaring property of two back-to-back diodes connected across output and inverting input of the op-amp, IC1B forms a rather straightforward fuzz circuit. The squared output signal coming from IC1B is converted into a triangle-shaped waveform by IC1C and related components. IC1D is wired as a virtual-earth mixer, summing the linear, squared and triangle-shaped signals coming from IC1A, IC1B and IC1C respectively. This is the figure of the circuit;

IC1A is the linear input amplifier. We can vary the input sensitivity of the circuit from -10dB to +10dB in three fixed steps by means of SW1, in order to cope with almost any pick-up type and model. We can done a very accurate mixing of these three different signals by means of P1, P3 and P4. The result will be an almost endless choice of different fuzz-effects.
[Circuit source: redcircuits.com]

Wide Voltage Range 1.8 Watt Audio Power Amplifier with Short Circuit Protection

2010-06-08T08:54:00.000+07:00

This is a design circuit for audio power amplifier using protection circuit. This circuit is based on LM4951A. This is the figure of the circuit;

The LM4951A is an audio power amplifier designed for applications with supply voltages ranging from 2.7V up to 9V. The LM4951A is capable of delivering 1.8W continuous average power with less than 1% THD+N into a bridge connected 8Ω load when operating from a 7.5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4951A does not require bootstrap capacitors, or snubber circuits.

The LM4951A features a low-power consumption active-low shutdown mode. Additionally, the LM4951A features an internal thermal shutdown protection mechanism and short circuit protection. The LM4951A contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4951A is unity-gain stable and can be configured by external gain-setting resistors.

[Circuit schematic source: National Semiconductor Notes]

Soft Light Dimmer Circuit

2010-06-08T08:50:00.000+07:00

This is circuit of soft light dimmer. This circuit uses the IGBT STGP10N50A and the TS555 timer as main components. This is the figure of the circuit;

The timer is triggered on the zero crossing voltage pulse. The time constant is determined by C5/R14+R15 that is used to determine the conduction angle. The T2 – T3 inhibits the power switch until the auxiliary supply voltage reaches 8V to guarantee that the gate of the IGBT receives correct voltage level.

R5 is the current sense resistor that is used for the short circuit and over-current protection. The gate of the IGBT will taken low and turn off, when the voltage across R5 reaches the sensitive gate thyristor gate trigger voltage. At the same time the timer will reset. This current limiting also provides protection against excessive in-rush current and automatic soft-start. [Source: STMicroelectronics Application Note]

10 Watt Stereo Amplifier Circuit Using TDA2009A

2010-06-08T08:44:00.000+07:00

This is a design circuit for amplifier. This amplifier circuit has a power of 10 watts. This amplifier circuit is very suitable to apply to your car audio. This amplifier is using IC TDA2009A, as amplifier power. To avoid excessive heat in the IC using some heat sink compound between the heat sink & the IC. C1 & C2 is the input coupling capacitor and blocks DC, as well as C10 & C11 which is the output capacitor Kopel, and C6 & C7 which blocks the DC from the feedback loop. R1/R2 (and R3/R4) set the level of feedback. This is the figure of the circuit.

Get together with 1 (R1/R2) = 68 or 37 dB. C8/R5 (and C9/R6) provides high frequency stability where loudspeaker inductive reactance load can become excessive. C4 and C5 provide power decoupling or filtering. Absolute maximum supply voltage is 28V for the amplifier.

Precision Clock Conditioners Low-Noise Clock Jitter Cleaner with Cascaded PLLs from the Power Wise

2010-05-18T20:09:00.002+07:00

The LMK04000 family of precision clock conditioners provides low-noise jitter cleaning, clock multiplication and distribution without the need for high-performance voltage controlled crystal oscillators (VCXO) module. Using a cascaded PLLatinum architecture combined with an external crystal and varactor diode, the LMK04000 family provides sub-200 femto second (fs) root mean square (RMS) jitter performance. This is the figure of the circuit;

The cascaded architecture consists of two high-performance phase-locked loops (PLL), a low-noise crystal oscillator circuit, and a high-performance voltage controlled oscillator (VCO). The first PLL (PLL1) provides a low-noise jitter cleaner function while the second PLL (PLL2) performs the clock generation. PLL1 can be configured to either work with an external VCXO module or use the integrated crystal oscillator with an external crystal and a varactor diode. When used with a very narrow loop bandwidth, PLL1 uses the superior close-in phase noise (offsets below 50 kHz) of the VCXO module or the crystal to clean the input clock. The output of PLL1 is used as the clean input reference to PLL2 where it locks the integrated VCO. The loop bandwidth of PLL2 can be optimized to clean the far-out phase noise (offsets above 50 kHz) where the integrated VCO outperforms the VCXO module or crystal used in PLL1.

The LMK04000 family features dual redundant inputs, five differential outputs, and an optional default-clock upon power up. The input block is equipped with loss of signal detection and automatic or manual selection of the reference clock. Each clock output consists of a programmable divider, a phase synchronization circuit, a programmable delay, and an LVDS, LVPECL, or LVCMOS output buffer. The default startup clock is available on CLKout2 and it can be used to provide an initial clock for the field-programmable gate array (FPGA) or microcontroller that programs the jitter cleaner during the system power up sequence.

Long Time Delays Circuit with 555 Timer

2010-05-18T20:08:00.002+07:00

This is a design circuit for a Long Time Delays using 555 Timer. In 555 Timer, a function of charging rate of the external capacitor is the timing. This circuit needs expensive capacitors with extremely low leakage. Practically, the components limit the time between pulse to around twenty minutes. To get longer time periods, we can connect both halves in tandem with a “divide-by” network in between. This is the figure of the circuit;

The first timer section is operated in an oscillatory mode. The periods of the first timer is 1/Fo. Then the “divide-by-N” network receives this signal and will generate the output signal with period of N/Fo. The second half of the 555 is triggered by the output signal of “divide-by-N”. So, the total time is now a function of Fo and N.

[Circuit source: Philips Semiconductor Application Note]

Infrared (IR) Proximity (Distance) Sensor Circuit

2010-05-18T20:05:00.000+07:00

The photodiode can be used to detect IR reflected from the object. However, IR produced by the ambient conditions also detected by the photodiode. This IR noise must be filtered to prevent false detections. Usually, the LED’s IR signal is modulated with a convenient frequency and then using that modulation to detect only IR to filter the IR noise. So, the photodiode will detect only IR reflected from the object. This method can be simplified by using the IR proximity sensor that has simple receiver and transmitter sections. This is the figure of the circuit;

The transmitter of this circuit consists of a 940nm IR LED (IR11-21C). To turn ON and OFF the IR LED, the a 10kHz oscillator frequency is used. we can control the detection and the level of transmitted power by varying the LED current. The transmit pulses of this transmitter have a small duty cycle (typically 10%), to save power.

The Op amp is biased at 2.5V because there no input IR signal present. The op amp output varies around 2.5V with a dynamic range of 5V because of a 10kHz IR signal incident. The output drives a simple diode detector. A DC signal proportional to its amplitude can be provided by a simple diode detector. Simple diode detector also rectifies the 10kHz signal. The output signal is an analog signal that is proportional to the distance of the object from the IR transmitter. We can fed the output signal to an ADC for further processing or use it directly.

[Circuit source: MAXIM Application Note]

PWM Speed Control Circuit Using Forward-Reverse and Regenerative Braking

2010-05-15T19:15:00.000+07:00

This is a circuit design for PWM Speed DC Motor Rotation circuit. This circuit has two functions, Forward-Reverse and Regenerative Braking function. This circuit is control by MOSFET. This is the figure of the circuit;

On this circuit, we can control the speed of DC 12V motor with Power MOSFET IRF150 using a signal PWM. The Relay RY1 work as control Reverse with the digital alarm, change Q10. The Relay RY2 work as function brake resistor. The F1 use to protect through the circuit by control Run or stop with the digital alarm. D1 is used to protect the current turn back from DC motor.

Infrared Remote Control Decoder Circuit

2010-05-15T19:13:00.000+07:00

This is a circuit for infrared Remote Control Decoder circuit. This circuit uses the SAA3049A which is used to check and convert the received coded data (RECS80/RC5) into latched binary outputs. This is the figure of the circuit;

We can uses several device in one location because the device address can be hard-wired for a particular address. The output of this device are the received data and address. This device has several feature such as it is suitable for low SAA3049A and low voltage supply current applications, it can accept RC5 codes with bi-phase transmission (SAA3006, SAA3010) or RECS80 codes with pulse position modulation (SAA3004, SAA3007, SAA3008) and it can Decodes 64remote control commands with a maximum of 32 sub-addresses. Besides that a maximum commands of this device is up to 2048 by adding circuitry for binary decoding, for example 1-of-16 decoder (HEF4515).

[Schematic source: NXP Semiconductor Application Notes]

Water Level Controller Circuit

2010-04-15T16:35:00.001+07:00

This is a design circuit for water level controller circuit that described here control the water level inside a tank. There two modes available with this water level controller circuit. The first mode is empty mode, when the controller will drain the tank if the water level reach the upper limit, the pump will be used to suck the water from the tank until the water level drop below the lower level. The second mode of this water level controller is fill mode. Here the pump will be used to fill the tank with the water when the water level is drop below the lower limit, the pump will be activated until the water level reach the upper limit. This is the figure of the circuit;

The circuit is use NOR logic gates, only one IC package and one transistor is needed for the active components, very simple design. The default position of push SW1 (as shown in the schematic diagram) is empty mode, just switch to other position to make the water level controller works in fill mode operation. The relay can be used to control almost any type of water pump motors. Please be aware that this circuit works only with water or other electrically conductive liquids.

Single Supply Instrumentation Amplifier Circuit

2010-04-15T16:33:00.000+07:00

This is a design circuit for a single supply instrumentation amplifier circuit. This circuit can be used to replace the function of conventional differential-amplifier topologies to load the DC gain on a low level signal. This circuit has high input impedance of non-inverting op-amp inputs. This is the figure of the circuit;

This circuit uses single supply, so the strain gauges are operated from Vcc. There is a disadvantage of this circuit a matched resistor is needed to build this circuit. That will suffer from poor CMRR. The circuit shown above can be modified by eliminating three resistors and by using only two op-amps. This is the figure of the modified circuit;

Two circuits above has some advantages and disadvantages. The disadvantages for first modified circuit are the two resistors must be changed instead of one and must be matched resistor. Besides that, the first stage cannot be used for gain. However, it will easy to calculate the gain of the circuit. The second modified circuit is not recommended because it may be unstable due to the operating of first op amp at less than unity gain. Besides that the propagation delay of the signal from Vin- is more than Vin+.
[Schematic circuit source: Texas Instruments Application Note]

Logic Probe with Pulse Indicator Circuit

2010-04-15T16:26:00.000+07:00

This is a circuit diagram for logic probe that is based on single CMOS IC. This logic probe shows three logic condition, High, Low, and Pulsing. Ind addition, there is no LED’s will glow if the probe input is neither hi or lo (the high impedance state of tri-output logic IC’s). This is the configuration of figure the circuit;

This logic probe using power from the logic circuit under test; CMOS IC enables logic circuit is used to test using voltages from 3 to 15 volts. IC1a is used as a buffer with a difference. Under no input, i.e. the gate will oscillate due to feedback from the 2M2 resistor since the probe not connected to circuit. IC1a output voltage is approximately half from supply voltage. The Hi and Lo logic indicator LED’s are connected to a potential divider. This potential divider consist of two 1K resistors. When there is no input, junction voltage is half supply voltage or high impedance no LED’s will glow. IC1a will rest in a permanent state because of Hi or Lo logic condition. This is indicated by either the Hi or Lo LED illuminating. Hi and Lo LEDs will light dimly with a fast oscillator or clock signal. This is the reason for IC1b and IC1c. These two gates form a mono stable oscillator, 100nF capacitor and 4M7 resistors determine the time constant. This is effectively slowed using clock signal as the mono stable is continually triggered and retriggered. IC1d works like a buffer to drive the pulsing LED.

12V Stroboscope Circuit

2010-04-15T16:24:00.002+07:00

Usually many stoboscope circuit work directly from mains voltage, but this circuit uses 12V DC instead on mains AC. The circuit has some special functions compared to other stroboscope circuits found electronics books. First the there is a switch for selecting the flash power: with C3 you can get very fast flash rates (over 50 Hz), C2 is most suitable for normal operation and using C1 directly you get very bright single flashes. This is the figure of the circuit;

The stoboscope tube needs about 250-400V DC to operate. This high voltage is generated using simple voltage step up circuit built from transistors Q1,Q2 and transformer T1. This circuit gives out about 230V AC voltage which is then rectified with rectifying bridge U1 (must have at least 400V voltage rating) and stored to the main capacitor C1. This approach gave me nice flash tube with reflector, trigger transformer and some of the capacitors (for example C1). Other parts were the one luying around.

Dual Input Far Field Noise Suppression Microphone Amplifier Circuit

2010-04-07T15:23:00.000+07:00

This is a circuit diagram for microphone amplifier. This circuit is using LMV1090 as based op amp signal in the circuit. This is the figure of the circuit;

The LMV1090 is a fully analog dual differential input, differential output, microphone array amplifier designed to reduce background acoustic noise, while delivering superb speech clarity in voice communication applications. The LMV1090 preserves near-field voice signals within 4cm of the microphones while rejecting far-field acoustic noise greater than 50cm from the microphones. Up to 20dB of far-field rejection is possible in a properly configured and using ±0.5dB matched microphones. [Schematic circuit source: National Semiconductor Notes].

Noise Floor Measurement Circuit of PLL Frequency Synthesizers

2010-03-31T04:44:00.000+07:00

Phase noise is a critical performance parameter of frequency synthesizers for wireless applications. RF system designers of phase modulated cellular systems, such as PHS, GSM and IS-54, need low noise local oscillator (L.O.) or frequency synthesizer blocks. This is a design circuit for the measurement system. This is the figure of the circuit;

The basic phase-lock-loop configuration we will be considering in the figure. The PLL consists of a high-stability crystal reference oscillator, a frequency synthesizer such as the National Semiconductor LMX2332TM, a voltage controlled oscillator (VCO), and a passive loop filter. The crystal reference used is the 10 MHz signal from the back of a spectrum analyzer at about +7 dBm or 1.42 VPP. The VCO used for this test was an ALPS URAE8x934 VCO with a tuning constant of 27 MHz/V phase locked at 900 MHz. By using a relatively wide loop filter bandwidth, (15 kHz for N = 4500) we are able to vary the reference frequency from 30 kHz to 400 kHz without changing the component values and maintain loop stability. The phase noise measurements were made at 150 Hz offset, to ensure that the data was on the flat portion of the curve “inside the loop”. At least 20 video averages were taken over a 1 kHz span for each measurement. In order to come up with the phase noise floor figure of merit the spectrum analyzer measurement must be normalized in terms of dBc/Hz, by subtracting 10 log of the resolution bandwidth used in the measurement. The noise is then referenced to the input of the phase detector by subtracting 20 log N.

[Circuit source: National Semiconductor Notes]

Low Cost IC Stereo Receiver Circuit

2010-03-31T04:39:00.000+07:00

The recent availability of a broad line of truly high-performance consumer integrated circuits makes it possible to construct a high quality, low noise, low distortion and low cost AM/FM/Stereo receiver. This is the complete design circuit for AM/FM/Stereo Receiver. This is the figure of the circuit;

This circuit is using LM3089FM for control the operation in this circuit. The LM3089 FM IF System does all the major functions necessary for FM processing, including a three stage amplifier/limiter and balanced product detector, as well as an audio preamplifier. A single quadrature coil was used for ease of alignment; yielding recovered audio with THD less than 0.5%, however a double coil may be used to diminish THD to 0.1% if required. Carrier level detectors provide delayed AGC, SIGNAL strength meter drive, and adjustable inter station mute control R11. The internal AFC amplifier was used to drive the TUNING meter, giving a visual indication of center tuning. FM stereo demodulation is accomplished by the use of the LM1800 phase locked loop, thereby eliminating the need for external coils. Only two adjustments are necessary: R14, which sets the 19 kHz oscillator, and R17, which corrects which corrects for excess phase shift thru the IF stages, and yields maximum channel separation. Automatic stereo/ monaural switching is built-in, and may be used in lieu of mechanical switching if desired. The open collector lamp driver is used to light a LED whenever a stereo station is encountered.

[Schematic diagram source: National Semiconductor Notes]

High Fidelity Stereo Power Amplifier Circuit

2010-03-31T04:30:00.000+07:00

This is a design circuit for audio power amplifier design utilizing the LM4702. This is a complete circuit for power amplifier design. This circuit has high quality circuit board layouts, the LM4702 power amplifier driver requires careful consideration. A good place to start is with the ground and power circuits design layout. This is the figure of the circuit;

Star connections for ground and power are always a good practice for audio circuit board layouts. A star connection is where there are individual traces from each component in the circuit that return to a central point. Notice how all the ground traces converge at the left side of the board, near Rs1 and Rs2, and connect to the two ground pins in the center of the power connector. The ground traces that connect to the right and left output jacks also converge at the center of the star ground which is the center of the power connector where the two ground pins are located.

[Circuit source: National Semiconductor Notes]

An Alternative Approach to Higher-Power Boost Converters

2010-03-31T04:28:00.000+07:00

This is a design circuit for high power boost converter circuit. This circuit is control by LM25037 Single chip IC. This circuit is a simple straightforward approach that can provide benefits over using a typical single gate-drive controller. This is the figure of the circuit;

The benefits can include higher step-up ratios and lower FET losses due to the reduction in transitional losses. Although there are a number of possible approaches to reduce total FET losses in higher-power boost converters, the equations in this article can be used to calculate total losses in the boost FETs for a number of different approaches. Considering the 150W boost converter example, it has been shown that total losses in the FETs are reduced when comparing the LM25037 dual-output gate-drive controller with the LM5020 single-output gate-drive controller.

[Schematic diagram source: National Semiconductor Notes]

Thermocouple Gauge Principle Operation

2010-03-24T13:07:00.000+07:00

The thermocouple gauge uses the thermal conductivity property of gases, by incorporating a wire filament which is heated by a constant source of power. Attached to this filament is a thermocouple, which measures the temperature of the wire. At high pressures, the large number of gas molecules striking the heated wire carries energy away and cools the wire. At low pressures, the smaller number of gas molecules striking the wire causes less cooling, and thus a higher temperature. This is the figure of the principle operation of the theory;

The thermocouple output voltage responds to these temperature changes to give an indication of pressure: low gas pressure gives high filament temperature which gives high thermocouple output voltage; high gas pressure gives low filament temperature which gives low thermocouple output voltage. The meter measuring the thermocouple voltage is calibrated in pressure units to give a direct indication of pressure. At pressures below about 10-3 torr, the heat loss from the filament is primarily through radiation since the density of gas molecules is so low. Since the heat loss due to radiation is constant, the resulting temperature corresponds to the “zero” reading on the meter. The thermocouple gauge is a simple, rugged device which is very useful at rough vacuum pressures. The meter covers the pressure range of 1 to 2000 millitorr. This is the schematic diagram of the thermocouple circuit.

[Schematic source: Duniway Stockroom Corp.]

Using Current Source to Make Linear Scale Analog Ohm Meter

2010-03-24T13:05:00.000+07:00

Many analog ohm meters have non linear scale, so the resolution become worse at higher resistance value. This because they use cheap current source, only a series resistance to approximate an ideal current source. An ideal current source will force a consistent current amount regardless of the tested resistor value. Using regulated current source, the current flowing through the tested resistor will be kept constant, so the measured voltage across the tested resistor is proportional (linear) to its resistance value. This is the figure of the circuit.

The current source is provided by IC1a. The two 1N4148 diodes give a constant reference, so the voltage across selected R2..R6 is constant at about 1.4 volt. The R1..R6 is selected to measure different resistor ranges. The VR1 has to be adjusted every time you switch for different range, just like as you do in your old classic analog ohmmeter.

Nonvolatile STANDBY/ON Switch Circuit

2010-03-24T13:00:00.002+07:00

STANDBY/ON switch below is appropriate for applications (industrial and telecom, for example) in which the circuitry must remember its state (STANDBY or ON) after a power failure that occurs when there is no operator. Because the state can be lost if leakage current drains the battery, we can not just rely on an alternative approach based on battery (or supercapacitor) and flip-flop. The other way is involving the use of a microcontroller and EEPROM, but software and a provision for startup time is required. A stand-alone EEPROM has an awkward interface for this application.

An electronically programmable voltage reference (IC4, DS4305) is used as a single-bit nonvolatile memory cell, that’s the idea. This device can be reprogrammed minimum of 50.000 times to remember the state of the STANDBY/ON switch, high or low output voltage. This is the figure of the circuit.

IC1 (MAX6766) is a kind of low-dropout (LDO) linear regulator with RESET output and the wide input-voltage range can be extended up to 72V. The control button (STANDBY/ON pushbutton) bounces can be eliminate by a uP (IC2,MAX6468). This IC supports the programming of IC4 by increasing the pause length between pulses. An inverter with Schmitt-trigger input(IC5) is driven by IC4 output, which in turn drives the gate of transistor Q2 to control the main power supply. [Circuit schematic source: MAXIM Application Note]

Board System Monitoring Circuit for Temperature and Voltage Condition

2010-03-24T12:59:00.000+07:00

This is a design circuit of board system monitoring for temperature and voltage condition. This circuit uses the NE1617A. The NE1617A is a 2 channel temperature sensor. It can measure remote and internal sensor. It also supports up to nine devices per bus. The temperature data update is selectable from 125 ms to 16 seconds, if it is used in normal operation. An internal, the temperature reading can be forced by one-shot command. This is the figure of the circuit.

The advantage of the NE1617A is programmable, has high accuracy, small, 16-pin QSOP packages and has an operating temperature of 0 to 120 °C. It can be used for applications where thermal monitoring of electrical components and hardware is critical. The more advanced version of the NE1617A is the NE1619. Besides measures the remote and internal temperature, the NE1619 can be used to monitor nine different voltages. It has programmable voltage and temperature limits for controlling internal alarms and supports two devices per bus. It also has an on-chip A/D converter which supports data collection and other functions. The consistent conversion rate that is used by the NE1619 is approximately 500 ms. [Circuit schematic source: NXP Application Note]

Reducing L200 Power Dissipation Circuit using Series Resistor

2010-03-13T08:35:00.000+07:00

It’s good to reduce the power dissipated by the device. Using resistor connected in series to the input (the left figure) is a simple and economic method to reduce the device input-output differential voltage. This is the figure of the design circuit;

Here’s the formula for calculating R:
R= [Vi min- (Vo+Vdrop)]/Io
Vdrop = minimum differential voltage between the input and the output of the device at current Io
Vin min = minimum voltage
Vo = Output voltage
Io = output current

Resistor R can be connected between pins 1 and 2 of the IC instead of in series with the input if the load is constant (the right figure). So, part of the load current flows through the device and part through the resistor. This configuration is available when the minimum current by the load is:
Io min = Vdrop/R

Low Pass Filter Circuit with Enhanced Step Response

2010-03-13T08:34:00.000+07:00

Effect on the system’s time-domain response is a common problem when designing low pass filters. The system may fail to recognize significant changes in time because pushing the cut-off frequency lower slows the step response. This is the figure of the circuit that present the low pass filter circuit;

On this circuit diagram, lower cut-off frequency is allowed without sacrificing the step-response time. The delta (difference) between the filter’s input and output is monitored by window comparator. The filter increases its slew rate by increasing its cut-off frequency an order of magnitude when the delta exceeds 50mV. Low pass-filtered by R4 and C3 is the original signal which is produce a cut-off frequency (312Hz) that reduces sensitivity to momentary glitches. The window-comparator input is drove by the filtered input. Comparator U2A or U2B will assert its output low if the input is outside the 50mV window. The low output drives Q5 into cutoff, causing its collector to presume a high impedance.

The filter’s cutoff frequency increases by ten times because the Q5 collector no longer grounds capacitor C2. The cutoff frequency throttles back to its quiescent state When the system output changes to within 50mV of the system input. This circuit diagram is configured for very low cutoff frequency, but changing C1 and C2 can rescale the configuration to higher frequency, where the oscillation frequency fOSC (in kHz) is 30 x 103/COSC (in pF) and the cutoff frequency is fOSC/100. For different window values in which the delta equals the resistance multiplied by 115µA, we can modify R2 and R3. The type of comparator must be an open-drain type.

Automatic Battery Backup Circuit

2010-03-13T08:32:00.000+07:00

This is a design schematic for battery backup circuit. The diode-OR connection is the simplest link between backup battery and a main supply with a load. But, when the battery voltage is greater than main supply voltage, it will not work. To solve this problem we can use the circuit below. This is the figure of the circuit;

This circuit has the backup supply of 9V battery and main switch-mode supply voltage ranges from 7V to 30V. It uses the MAX931 which is an ultra-low-power comparator with a 1.182V band gap reference. When it is used in normal condition, the battery’s negative terminal floats, the three parallel-connected n-channel FETs are off, and the comparator output is low. The n-FETs will turning on, the negative terminal of the battery will be grounded and the comparator’s output goes high when the main voltage declines to 7.4V.

To eliminate the supply-rail glitch that would otherwise happen when switching from the battery to the main supply, the delay was used. It can be done by using the R6, C1, and D1. An unacceptable reset in the system’s microcontroller can be occurred while the glitches. For proper operation, the value of R3 and R4 should set the hysteresis in the MAX931 to 800mV. [Circuit Source: maxim-ic.com]

Zener Diode Tester Circuit

2010-03-11T12:16:00.000+07:00

This is a circuit for is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. This is the figure of the circuit.

Transistor T1 (BC547) is configured as an oscillator and driver to obtain required AC voltage across transformers 230V AC terminals. This AC voltage is converted to DC by diode D1 and filter capacitor C2 and is used to test the zener diodes. R3 is used as a seri-es current limiting resistor. After assembling the circuit, check DC voltage across points A and B without connecting any zener diode. Now switch on S1. The DC voltage across A-B should vary from 10V to 120V by adjusting potentiometer VR1 (10k). If every thing is all right, the circuit is ready for use. For testing a zener diode of unknown value, connect it across points A and B with cathode towards A. Adjust potentiometer VR1 so as to obtain the maximum DC voltage across A and B. Note down this zener value corresponding to DC voltage reading on the digital multi meter. When testing zener diode of value less than 3.3V, the meter shows less voltage instead of the actual zener value. However, correct reading is obtained for zener diodes of value above 5.8V with a tolerance of 10per cent. In case zener diode shorts, the multi meter shows 0 volts

10 Watt Stereo Amplifier Circuit Using TDA2009A

2010-03-11T12:14:00.000+07:00

AC Power Supply Low Voltage

2010-02-11T19:16:00.000+07:00

This is an AC power supply circuit with low voltage output (step down transformer converter). Notes! This project involves the use of dangerous voltages. You must make sure all high-voltage (120 volt household power) conductors are safely insulated from accidental contact. No bare wires should be seen anywhere on the “primary” side of the transformer circuit. Be sure to solder all wire connections so that they’re secure, and use real electrical tape (not duct tape, scotch tape, packing tape, or any other kind!) to insulate your soldered connections. If you wish to enclose the transformer inside of a box, you may use an electrical “junction” box, obtained from a hardware store or electrical supply house. If the enclosure used is metal rather than plastic, a three-prong plug should be used, with the “ground” prong (the longest one on the plug) connected directly to the metal case for maximum safety.

Before plugging the plug into a wall socket, do a safety check with an ohmmeter. With the line switch in the “on” position, measure resistance between plug prong and the transformer case. There should be infinite (maximum) resistance. If the meter registers continuity (some resistance value less than infinity), then you have a “short” between one of the power conductors and the case, which is dangerous!

Next, check the transformer windings themselves for continuity. With the line switch in the “on” position, there should be a small amount of resistance between the two plug prongs. When the switch is turned “off,” the resistance indication should increase to infinity (open circuit — no continuity). Measurement the resistance between pairs of wires is on the secondary side. These secondary windings should register much lower resistances than the primary. Why is this?

Plug the cord into a wall socket and turn the switch on. You should be able to measure AC voltage at the secondary side of the transformer, between pairs of terminals. Between two of these terminals, you should measure about 12 volts. Between either of these two terminals and the third terminal, you should measure half that. This third wire is the “center-tap” wire of the secondary winding.

Relay Toggle Circuit Using 555 Timer IC

2010-02-11T19:11:00.000+07:00

This circuit is a design for relay toggle circuit. This circuit below toggles a relay when a button is pressed. Pins 2 and 6, the threshold and trigger inputs, are held at 1/2 the supply voltage by the two 10K resistors. When the output is high, the capacitor is charges through the 100K resistor, and discharges when the output is low. When the button is pressed, the capacitor voltage is applied to pins 2 and 6 which causes the output to change to the opposite state. When the button is released, the capacitor will charge or discharge to the new level at the output (pin 3). The parts are not critical, the resistors can be somewhat higher or lower, but the 2 resistors at pins 2 and 6 should be equal values, and the resistor connected to the cap should be 10 times greater or more. This is the figure of the circuit.

Advantages of this circuit are the large hystersis range at the input which avoids false triggering, and only a few parts are needed for construction. One disadvantage is the relay may be engaged when power is first applied. To solve this problem, you could tie the reset line (pin 4) to another resistor/capacitor combination with the capacitor at ground and the resistor at the +V point. This will cause pin 4 to be held near ground for a short period which will reset the output when power is applied. The 100 ohm resistor and 100uFcapacitor serve to filter noise on the supply line if the circuit is used in a automotive application.

Car Anti Theft Wireless Alarm Circuit

2010-02-11T19:07:00.000+07:00

This is a design circuit for alarm. This circuit is for an anti- theft wireless alarm can be used with any vehicle having 6 to 12 volt DC supply system. The mini VHF FM radio-controlled, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit of the wireless alarm uses an CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. This is the figure of the circuit.

Receiver is tuned to the transmitter’s frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energized. When an intruder tries to drive the car and takes it a few meters away from the car porch, the radio link between the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circuit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2. Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on.

Astable Circuit Produce Pulses Using 555 Timer IC

2010-02-11T19:03:00.000+07:00

This is circuit that first introduced by Signetics Corporation as the SE555/NE555 about 1971. Pin connections and functions: (See schematic below for basic circuits). Pin 1 (Ground) – The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common when operated from positive supply voltages. Pin 2 (Trigger) – This pin is the input which causes the output to go high and begin the timing cycle. Triggering occurs when the trigger input moves from a voltage above 2/3 of the supply voltage to a voltage below 1/3 of the supply. This is the figure of the circuit.

For example using a 12 volt supply, the trigger input voltage must start from above 8 volts and move down to a voltage below 4 volts to begin the timing cycle. The action is level sensitive and the trigger voltage may move very slowly. To avoid retriggering, the trigger voltage must return to a voltage above 1/3 of the supply before the end of the timing cycle in the mono stable mode. Trigger input current is about 0.5 micro amps. Pin 3 (Output) – The output pin of the 555 moves to a high level of 1.7 volts less than the supply voltage when the timing cycle begins. The output returns to a low level near 0 at the end of the cycle. Maximum current from the output at either low or high levels is approximately 200 mA. Pin 4 (Reset): – A low logic level on this pin resets the timer and returns the output to a low state. It is normally connected to the + supply line if not used.

Pin 5 (Control) – This pin allows changing the triggering and threshold voltages by applying an external voltage. When the timer is operating in the astable or oscillating mode, this input could be used to alter or frequency modulate the output. If not in use, it is recommended installing a small capacitor from pin 5 to ground to avoid possible false or erratic triggering from noise effects. Pin 6 (Threshold) – Pin 6 is used to reset the latch and cause the output to go low. Reset occurs when the voltage on this pin moves from a voltage below 1/3 of the supply to a voltage above 2/3 of the supply. The action is level sensitive and can move slowly similar to the trigger voltage. Pin 7 (Discharge) – This pin is an open collector output which is in phase with the main output on pin 3 and has similar current sinking capability. Pin 8 (V +) – This is the positive supply voltage terminal of the 555 timer IC. Supply-voltage operating range is +4.5 volts (minimum) to +16 volts (maximum).

Automatic School Bell Circuit

2010-01-24T22:36:00.000+07:00

This is a design circuit for alarm, but it can be used for school bell. This circuit is based on two IC. There are 555 timer IC and CD4017 IC. This is the figure of the circuit.

To ring this automatic school bell to start the first period, the peon needs to momentarily press switch S1. Thereafter, the bell sounds every 45 minutes to indicate the end of consecutive periods, except immediately after the fourth period, (IC2 and IC3) and AND gate CD4081 (IC4). Timer IC1 is wired as an astable multi vibrator, whose clock output pulses are fed to IC2. IC2 increases the time periods of IC1 (4.5 and 3 minutes) by ten times to provide a clock pulse to IC3 every 45 minutes or after 30 minutes, respectively. When the class periods are going on, the outputs of IC3 switch on transistors T1 and T2 via diodes D4 through D12.

Resistors R4 and R5 connected in series to the emitter of npn transistor T2 gate. When SCR1 is fired, it provides ground path to operate the circuit after resetting both decade counters IC2 and IC3. At the same time, LED1 glows to indicate that school bell is now active.

A/D Conversion Circuit for Single-Ended MSB First Mode

2010-01-24T22:35:00.000+07:00

This is a design circuit for analog to digital converter that can be used in data acquisition. This circuit is based on ADC0833 and controlled by INS8048. Before explaining the system configuration, it is worthwhile for one to understand the operation of the INS8048 processor's I/O ports. Ports 1 and 2 are quasi-bidirectional; that is, they can be used as inputs or outputs while being statically latched. If a ``1'' is written into any port bit, that bit can function as an input or as a high level output. If a ``0'' is written into any port bit, that bit can function only as a low level output.

Outputs are latched until changed and inputs are unlatched and must be read immediately. When used with the ANL Pp, A (AND accumulator to port) or the ORL Pp, A (OR accumulator to port) instructions, these ports provide an efficient means of handling single line inputs and outputs. Port expansion, if anticipated, is handled via the lower four bits of Port 2. Only four pins of the processor's Port 1 or Port 2 are needed for physical interfacing. The ANL or ORL instructions set up the port pins to produce the proper outputs (CS, CLK, and the multiplex address) or to allow for data input from the A/D converter.

[Circuit schematic source: National Semiconductor Notes].

Water Level Sensor Circuit Using LM1830 Single Chip

2009-12-31T04:46:00.000+07:00

This is a water sensor circuit design using based on a Conductive Liquid Level Sensor, this single chip circuit is very compact and simple. This circuit is an ac excited fluid level sensor, which uses alternating current to provide biasing for the sensor probe to avoid electrolysis of the probes. This ac excitation makes the sensing probe has longer lifetime. This circuit can be useful for wide range of water or liquid level sensing and control such as radiators, beverage dispensers, washing machines, water softeners, irrigation, reservoirs, boilers, aquarium, or sump pumps

Many type of fluids are electrically conductive and can be detected using this liquid level sensor circuit: city water/ground water, sea water, chopper sulfate solution, weak acid, weak base, household ammonia, water and glycol mixture, wet soil, coffee, or fruit juices. Remember that most of fuel doesn’t conduct electricity, so this circuit can be employed as fuel level sensor/detector. This is the figure of the circuit.

If we look at its data sheet, this water level sensor circuit chip is best at 10-24 volt supply voltage. The absolute maximum voltage supply for this liquid level sensor chip is 28V, but remembers to always try to avoid this extreme condition to prevent damaging the chip.

In the first circuit, a basic low level warning application uses a LED to indicate the water level falls below the sensor. You can see the filter pin (9) is not connected, this means that the LED is actually blinking at sound frequency, but it’s fine since our eye response is slow enough to notice such high speed blinking. Since without filter capacitor at pin 9 the output give a square wave signal, you can easily replace the led with loud speaker as shown in the second circuit to give audio indication. If you need a TTL or CMOS level then you should use a filtering capacitor connected to pin 9 and use the open collector output to drive a pull up resistor connected to a voltage supply at desired voltage level. For water level control, or any conductive liquid level control, you can use a relay to activate a motor or valve to control the level. The third circuit show this kind of application, and the relay can be seen as liquid/water level switch. The optional resistor seen in the third circuit is an option for high voltage transient that often occurs in automotive environment, and you can omit it if there is no such possibility. [Circuit's schematic diagram source: National Semiconductor Application Notes]

Amplitude Average Detector Circuit

2009-12-30T21:23:00.000+07:00

This is a design circuit for sensing amplitude. This circuit is similar peak detector. But the output won’t immediately follow the input peaking. Because the output follows the input peak slowly, averaging effect will be seen at the output. This is the figure of the circuit.

This circuit is work based on two IC’s, there are LM307 and LF351. Use 1% resistor for R1, R2, R3, and R4, and you can achieve negative and positive cycle difference of 0.5dB at the worst case. If you use 5% resistors then the difference between positive and negative cycle gain difference would be about 2dB (worst case). The averaging time constant will depend on R5-C2, you can change to other values if needed. [Circuit's diagram source: National Semiconductor Application Notes].

Headphone Buffer Amp Circuit

2009-12-25T06:54:00.000+07:00

This is a design circuit for headphone buffer amplifier. This circuit is work based on 5532 IC. This is the figure of the circuit.

The key component is the 5532 Dual Op Amp. While ordinarily this part is chosen for it's low noise characteristics, it is also capable of delivering nearly 350mW of output power per side, more than enough to drive headphones. The circuit can operate from bipolar voltages from +/-5V to +/-18V and it is not absolutely necessary that the + and - supply voltages be the same magnitude. The superior supply voltage rejection of the IC allows operation with unregulated supplies.

Dual Channel Digital Volume Control Circuit

2009-12-25T06:47:00.000+07:00

This circuit is design for control the volume audio. This circuit for replacing your manual volume control in a stereo amplifier. This circuit is control by three IC, there are 555 timer, 74LS193, and 4066. This is the figure of the circuit.

IC1 timer 555 is configured as an astable flip-flop to provide low-frequency pulses to up/down clock input pins of pre-stable up/down counter 74LS193 (IC2) via push-to-on switches S1 and S2. To vary the pulse width of pulses from IC1, one may replace timing resistor R1 with a variable resistor. Operation of switch S1 (up) causes the binary output to increment while operation of S2 (down) causes the binary output to decrement. The maximum count being 15 (all outputs logic 1) and minimum count being 0 (all outputs logic 0), it results in maximum and minimum volume respectively.