Voltage Regulator Circuit with Pass Transistor

This is a simple design for Voltage Regulator Circuit using pass transistor. The design has built by LM317T. The LM317T output current can be increased by using an additional power transistor to share a portion of the total current. The amount of current sharing is established with a resistor placed in series with the 317 input and a resistor placed in series with the emitter of the pass transistor. The circuit is show in the figure below.


In the figure, the pass transistor will start conducting when the LM317 current reaches about 1 amp, due to the voltage drop across the 0.7 ohm resistor. Current limiting occurs at about 2 amps for the LM317 which will drop about 1.4 volts across the 0.7 ohm resistor and produce a 700 milli volt drop across the 0.3 ohm emitter resistor. Thus the total current is limited to about 2+ (.7/.3) = 4.3 amps.

The input voltage will need to be about 5.5 volts greater than the output at full load and heat dissipation at full load would be about 23 watts, so a fairly large heat sink may be needed for both the regulator and pass transistor. The filter capacitor size can be approximated from C=IT/E where I is the current, T is the half cycle time (8.33 mS at 60 Hertz), and E is the fall in voltage that will occur during one half cycle. To keep the ripple voltage below 1 volt at 4.3 amps, a 36,000 uF or greater filter capacitor is needed. The power transformer should be large enough so that the peak input voltage to the regulator remains 5.5 volts above the output at full load, or 17.5 volts for a 12 volt output. This allows for a 3 volt drop across the regulator, plus a 1.5 volt drop across the series resistor (0.7 ohm), and 1 volt of ripple produced by the filter capacitor. A larger filter capacitor will reduce the input requirements, but not much.

Variable Voltage Regulator Circuit Using LM317T

This is a Variable Voltage Regulator Circuit that is built by LM317T IC. The LM317T is an adjustable 3 terminal positive voltage regulator capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof. This circuit can be use to make a stable power supply. You can looks the circuit diagram from the figure.


The principle work of the circuit is output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100uA. The output voltage can be closely approximated from Vout=1.25 * (1+(R2/R1)) which ignores the adjustment terminal current but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120 ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA. The example below shows a LM317 used as 13.6 volt regulator. The 988 ohm resistor for R2 can be obtained with a standard 910 and 75 ohm in series.

When power is shut off to the regulator the output voltage should fall faster than the input. In case it doesn't, a diode can be connected across the input/output terminals to protect the regulator from possible reverse voltages. A 1uF tantalum or 25uF electrolytic capacitor across the output improves transient response and a small 0.1uF tantalum capacitor is recommended across the input if the regulator is located an appreciable distance from the power supply filter. The power transformer should be large enough so that the regulator input voltage remains 3 volts above the output at full load, or 16.6 volts for a 13.6 volt output.

Tone Generator Circuit Using 555 IC

This tone generator circuit is a basic 555 square wave oscillator that is used to produce a 1 Khz tone from an 8 ohm speaker. There are two type of circuit that can be using. Each the type have same characteristic, but have different operation. This is the both circuit that can be studied in this figure.


Operation circuit in the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near square wave. Lower frequencies can be obtained by increasing the 6.2K value, higher frequencies will probably require a smaller capacitor as R1 cannot be reduced much below 1K. Lower volume levels can be obtained by adding a small resistor in series with the speaker (10-100 ohms).

In the circuit on the right, the speaker is directly driven from the 555 timer output. The series capacitor (100 uF) increases the output by supplying an AC current to the speaker and driving it in both directions rather than just a pulsating DC current which would be the case without the capacitor. The 51 ohm resistor limits the current to less than 200 mA to prevent overloading the timer output at 9 volts. At 4.5 volts, a smaller resistor can be used.

Low Power FM Transmitter Circuit Using Transistor

The circuit of the FM transmitter is shown in the figure is simple design. The first stage is the oscillator, and is tuned with the variable capacitor. This circuit is use two transistor BC549 as op amp the input signal. Select an unused frequency, and carefully adjust C3 until the background noise stops. Because the trimmer cap is very sensitive, make the final frequency adjustment on the receiver. When assembling the circuit, make sure the rotor of C3 is connected to the +9V supply. This ensures that there will be minimal frequency disturbance when the screwdriver touches the adjustment shaft. You can use a small piece of non copper-clad circuit board to make a screwdriver - this will not alter the frequency.

How does this circuit work? The frequency stability is improved considerably by adding a capacitor from the base of Q1 to ground. This ensures that the transistor operates in true common base at RF. A value of 1nF (ceramic) as shown is suitable, and will also limit the HF response to 15 kHz, this is a benefit for a simple circuit like this, and even commercial FM is usually limited to a 15 kHz bandwidth. Q1 is the oscillator, and is a conventional design. L1 and C3 (in parallel with C2) tune the circuit to the desired frequency, and the output (from the emitter of Q1) is fed to the buffer and amplifier Q2. This isolates the antenna from the oscillator giving much better frequency stability, as well as providing considerable extra gain. L2 and C6 form a tuned collector load, and C7 helps to further isolate the circuit from the antenna, as well as preventing any possibility of short circuits should the antenna contact the grounded metal case that would normally be used for the complete transmitter.

The audio signal applied to the base of Q1 causes the frequency to change, as the transistor's collector current is modulated by the audio. This provides the frequency modulation (FM), that can be received on any standard FM band receiver. The audio input must be kept to a maximum of about 100mV, although this will vary somewhat from one unit to the next. Higher levels will cause the deviation (the maximum frequency shift) to exceed the limits in the receiver usually ± 75 kHz. With the value shown for C1, this limits the lower frequency response to about 50 Hz (based only on R1, which is somewhat pessimistic), if you need to go lower than this, then use a 1uF cap instead, which will allow a response down to at least 15 Hz. C1 may be polyester or mylar, or a 1uF electrolytic may be used, either bipolar or polarized. If polarized, the positive terminal must connect to the 10k resistor.

High Current Regulated Supply Circuit Using LM317

The high current regulator circuit is built uses an additional winding or a separate transformer to supply power for the LM317 regulator so that the pass transistors can operate closer to saturation and improve efficiency. For good efficiency the voltage at the collectors of the two parallel 2N3055 pass transistors should be close to the output voltage. The operation of this circuit is explained like this.


The LM317 requires a couple extra volts on the input side, plus the emitter/base drop of the 3055s, plus whatever is lost across the (0.1 ohm) equalizing resistors (1volt at 10 amps), so a separate transformer and rectifier/filter circuit is used that is a few volts higher than the output voltage. The LM317 will provide over 1 amp of current to drive the bases of the pass transistors and assumption a gain of 10 the combination should deliver 15 amps or more.

The LM317 always operates with a voltage difference of 1.2 between the output terminal and adjustment terminal and requires a minimum load of 10mA, so a 75 ohm resistor was chosen which will draw (1.2/75 = 16mA). This same current flows through the emitter resistor of the 2N3904 which produces about a 1 volt drop across the 62 ohm resistor and 1.7 volts at the base. The output voltage is set with the voltage divider (1K/560) so that 1.7 volts is applied to the 3904 base when the output is 5 volts. For 13 volt operation, the 1K resistor could be adjusted to around 3.6K. The regulator has no output short circuit protection so the output probably should be fused.

Guitar Pre Amp Using TL072

The preamp circuit is shown in the figure has a few interesting characteristics that separate it from the "normal" assuming that there is such a thing. The circuit is built by TL072 as amp. This is simple design and provides excellent tonal range. The gain structure is designed to provide a huge amount of gain, which is ideal for those guitarists who like to get that fully distorted "fat" sound. The circuit is show in this figure;


However, with a couple of simple changes, the preamp can be tamed to suit just about any style of playing. Likewise, the tone controls as shown have sufficient range to cover almost anything from an electrified violin to a bass guitar. The response can be limited if you wish (by experimenting with the tone control capacitor values).

The preamp uses a dual op amp as its only amplification. The lone transistor is an emitter follower, and maintains low output impedance after the master volume control. As shown in the figure, with a typical guitar input, it is possible to get a very fat overdrive sound by winding up the volume, and then setting the master for a suitable level. The overall frequency response is deliberately limited to prevent extreme low-end waffle, and to cut the extreme highs to help reduce noise and to limit the response to the normal requirements for guitar. If you use the TL072 op amp as shown, you may find that noise is a problem, especially at high gain with lots of treble boost. I strongly suggest that you use an OPA2134 a premium audio op, you will then find this quite possibly the quietest guitar amp you have ever heard. At any gain setting, there is more pickup noise from the guitar than circuit noise and for the prototype pre amp used carbon resistors.

Cell Lithium Ion Charger Circuit

This circuit was build to charge two series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. This operation using LM339 to amp the signal input. The charger will operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage. When the battery is low, the current pulses are spaced close together so that a somewhat constant current is present. As the batteries reach full charge, the pulses are spaced farther apart and the full charge condition is indicated by the LED blinking at a slower rate. The below figure is about the circuit of the charger.


A TL431, band gap voltage reference (2.5 volts) is used on pin 6 of the comparator so that the comparator output will switch low, triggering the 555 timer when the voltage at pin 7 is less than 2.5 volts. The 555 output turns on the 2 transistors and the batteries charge for about 30 milliseconds. When the charge pulse ends, the battery voltage is measured and divided down by the combination 20K, 8.2K and 620 ohm resistors so that when the battery voltage reaches 8.2 volts, the input at pin 7 of the comparator will rise slightly above 2.5 volts and the circuit will stop charging.

The circuit could be used to charge other types of batteries such as Ni-Cad, Ni-Mh or lead acid, but the shut-off voltage will need to be adjusted by changing the 8.2K and 620 ohm resistors so that the input to the comparator remains at 2.5 volts when the terminal battery voltage is reached. Be careful not to overcharge the batteries. I would recommend using a large capacitor in place of the battery to test the circuit and verify it shuts off at the correct voltage.

AM RF Amplifier for External Antenna Using FET

It is would suggest that this RF amp would be most helpful when used with the AM loop antenna. In this case, this circuit is simply deleted T1, which is mounted off the board anyway. C1 will serve as the tuning capacitor for the loop. This is the figure circuit;


If a long wire antenna is used with (or without) a coupler, you will need T1. T1 is an AM RF transformer, and is a type that is becoming increasingly difficult to find. An AM loop stick antenna could probably be substituted, with the smaller number of turns being used for the secondary. I would suggest using a small ferrite slug, or breaking off the excess length of ferrite.

I have no idea whether the RCA 40468A FET is still available or not. It came in a 4 pin metal can with the 4th pin connected to the substrate. I have successfully substituted other N-channel devices, such as the HEP-802, which comes in a plastic TO-92 package. Simply ignore the substrate connection. Other good quality N-channel FET's can probably be used as well. Both articles stressed handling precautions for FET's. Even though FET's today are much better protected than in the past, static can still damage them. Use a wrist strap and grounded soldering station during assembly. I cann’t give enough praise to this design. It provides about 40dB of gain, and the main problem you will encounter is overloading.
Source; Bruce Carter

-5 Volt Generating Circuit Using 555 Timer IC

The generator circuit using 555 IC is a simple model to produce negative voltage. This voltage is resulted by 9 Volt batteries. The simple figure is shown in below. A 555 timer can be used to generate a square wave to produce a negative voltage relative to the negative battery terminal.


Operation of this circuit is starting when the timer output is at pin 3 goes positive, the series 22 uF capacitor charges through the diode (D1) to about 8 volts. When the output switches to ground, the 22 uF cap discharges through the second diode (D2) and charges the 100 uF capacitor to a negative voltage. The negative voltage can rise over several cycles to about -7 volts but is limited by the 5.1 volt zener diode which serves as a regulator. Circuit draws about 6 milliamps from the battery without the zener diode connected and about 18 milliamps connected. Output current available for the load is about 12 milliamps. An additional 5.1 volt zener and 330 ohm resistor could be used to regulate the +9 down to +5 at 12 mA if a symmetrical +/- 5 volt supply is needed. The battery drain would then be around 30 mA.

100W Guitar Amplifier Using TIP36C Transistor

The power amp circuit is built using TIP35/36C transistor, the output stage is deliberately massive overkill. This ensures reliability under the most arduous stage conditions. No amplifier can be made immune from everything, but this does come close. The power amp is loosely based on the 60 Watt amp previously, but it has increased gain to match the preamp. Other modifications include the short circuit protection the two little groups of components next to the bias diodes (D2 and D3). This new version is not massively different from the original, but has adjustable bias, and is designed to provide a "constant current" output to the speakers. This circuit is achieved using R23 and R26. Note that with this arrangement, the gain will change depending on the load impedance, with lower impedances giving lower power amp gain. This is not a problem, so may safely be ignored. The figure is show the circuit;


The principle work and specification guitar power amplifier is power transistors will have an easy time driving any load down to 4 ohms. If you don't use the PCB, you can use TO3 transistors for the output stage. MJ15003/4 transistors are very high power, and will run cooler because of the TO-3 casing (lower thermal resistance). Beware of counterfeits though! There are many other high power transistors that can be used, and the amp is quite tolerant of substitutes (as long as their ratings are at least equal to the devices shown). The PCB can accommodate Toshiba or Motorola 150W flat-pack power transistors with relative ease, if you wanted to go that way. TIP3055/2966 or MJE3055/2955 can also be used for light or ordinary duty.

At the input end that is shown in the figure, there is provision for an auxiliary output, and an input. The latter is switched by the jack, so you can use the "Out" and "In" connections for an external effects unit. Alternatively, the input jack can be used to connect an external preamp to the power amp, disconnecting the preamp. The speaker connections allow up to two 8 Ohm speaker cabinets (giving 4 Ohms). Do not use less than 4 ohm loads on this amplifier. It is not designed for it, and will not give reliable service!

1.5 Volt LED Flashers Circuit

The LED flasher circuits below operate on a single 1.5 volt battery. There are 4 types that you can look and make. It is must appropriates with your condition. The circuit can build by LM3909, but you must read LM3909 data sheet to make a good result. Otherwise, this design can build by transistor. This is the figure of the circuit.


The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED. The top left circuit, designed by Andre De-Guerin illustrates using a 100uF capacitor to double the battery voltage to obtain 3 volts for the LED. Two sections of a 74HC04 hex inverter are used as a square wave oscillator that establishes the flash rate while a third section is used as a buffer that charges the capacitor in series with a 470 ohm resistor while the buffer output is at +1.5 volts. When the buffer output switches to ground (zero volts) the charged capacitor is placed in series with the LED and the battery which supplies enough voltage to illuminate the LED. The LED current is approximately 3 mA, so a high brightness LED is recommended.

In the other two circuits, the same voltage doubling principle is used with the addition of a transistor to allow the capacitor to discharge faster and supply a greater current (about 40 mA peak). A larger capacitor (1000uF) in series with a 33 ohm resistor would increase the flash duration to about 50mS. The discrete 3 transistor circuit at the lower right would need a resistor (about 5K) in series with the 1uF capacitor to widen the pulse width.

MULTI SWITCH DOORBELL Circuit Using CD4042B

This circuit is built by CD4042 IC. The input of the design is result musical doorbell. CD4042B IC is popular IC to built up the voice of the bell. There are four data input that it will shown by LED (D1-D4). It will “on” if the main switch (S6) is turn on. The circuit figure is shown in below;


The principle work is when switch S6 is pushed to ‘on’ condition, the circuit gets +9V and the four data inputs (D1 through D4) of IC are in low state because these are tied to ground via resistors R1 through R4. Polarity input in pin 6 of CD4042B IC is also pulled down by resistor R5. Clock input (pin 5) of the quad D-latch is wired in normally low mode and hence all the four outputs (Q0 through Q3) have the same states as their corresponding data inputs. As a result, LED1 through LED4 are in off condition. There are four switches fitted at four different doors/gates outside the home and a monitoring panel in the common room of the home. If any switch is pressed by a visitor pins 2 and 4 of IC go high.

Simultaneously, pin 3 to IC (Q0 output) go low and LED1 starts glowing to indicate that switch S1 is pressed. Output in pin 13 of the dual 4-input NOR gate (IC2, here wired as a single 4-input OR gate) is high to forward bias buzzer driver transistor T1 via resistor R10. The final result is a soft and pleasing musical bell, which lasts until reset switch S5 is pressed by the owner. For this latching arrangement, output pin 13 of IC2 from the NOR gate is fed back to the clock input of IC1. The circuit costs around Rs 100.

Reduces noise and ripple circuit for audio band

The circuit in the figure is reduces noise and ripple circuit by at least 35 dB over the audio range of 100 Hz to 20 kHz. This reduces noise and ripple circuit provides a clean source of 5V power for driving audio circuits in portable applications such as cellular phones and multimedia notebook computers. Most linear regulators reject noise only to about 100 Hz, and the bulk of a low-frequency passive filter is unwelcome in portable applications. The figure is show below;


The principle work of the circuit accepts noisy VCC in the range of 4.5 to 6V and produces quiet VCC at a dc level 7% lower than the input. For example, the circuit produces 4.65V at 1A from a nominal 5V source, with only 200 µA of quiescent current. The layout is small; the circuit consists of one SOT-23 transistor, one shrink SO-8 op amp, and a few passive components. The largest capacitor is 10 µF, and the resistors can be 0.1W or surface-mount 0805. The circuit acts as a wide-bandwidth buffered voltage follower (not a regulator) with a dc output level that is 7% below that of VIN. R1 and R3 form a voltage divider that provides the 7% attenuations, and C1 helps to form a 93% filtered replica of VIN at the op amp’s inverting input. The op amp’s small input-bias current (typically 25 nA) allows large resistor values for R1 and R3, yet limits the maximum dc error to only 20 mV. The result is a low-pass filter with a 2-Hz corner frequency that provides 20 dB of attenuation at 20 Hz.

Because the op amp’s common-mode input range extends from rail to rail, its noninverting input can directly sample the output voltage. R2 and C2 filter the op amp’s supply voltage to provide the op amp with a lower output impedance and better power-supply rejection at high frequencies. This filter’s 300-Hz roll-off augments the op amp’s already high 110-dB PSRR.

Battery Discharge Monitor Using TL431

This is a battery monitor circuit which disconnect the load when the battery is discharged, preventing a deep discharge which could cause permanent battery damage. The battery is automatically reconnected when a battery charger or other DC source is connected across the load. Select a relay which requires less than 100ma coil current and with contacts capable of handling the load and charging currents. This figure is about the circuit.


The principle work of the circuit is C1 should be about one hundred micro-farads and C2 may be near 1 micro-farad. C2 simply delays the closing of the relay long enough for C1 to charge and C1 keeps the relay closed long enough for the battery voltage to climb above the cut-off point (about 22 volts for the circuit as shown). The 210k resistor may be reduced to 92k for 12 volt batteries. These R1 values may be reduced if a lower drop-out voltage is desired. The circuit may cycle on and off several times if the battery is deeply discharged with a delay proportional to the value of C1. The load sees the full voltage of the charger before the relay connects the battery in this circuit and in some applications the version below may be more desirable.

Power Supply Monitor Using LM3914

This circuit is use to a few resistors and some LED, a simple expanded-scale voltmeter is easily constructed. Furthermore, it runs from the same single 5V ± 10% supply it monitors and can provide TTL compatible under voltage and over voltage warning signals. The complete circuit is shown in this figure.


This circuit is useful where quick and easy voltage adjustments must be made, such as in the field or on the production line. The circuit’s low cost makes it feasible to incorporate it into the system, where the overvoltage and under voltage warning signals provide an attractive extra. Of course, these techniques can be used to monitor any higher voltages, positive or negative. Calibration procedure is the LM3914 output thresholds have been shifted up by 100 mV and output #10 is or-tied with output #9. Other outputs may be wire or together if 100 mV resolution is not necessary. If desired, the outputs can be color coded by making LED #1 and LED #10 red, LED #2 and LED #9 amber, and the rest of the LEDs green to ease interpretation.

To calibrate, set VCC at 5.41V and adjust R6 until LED #9 and LED #10 are equally illuminated. (A built-in overlap of about 1 mV ensures all LEDs won’t go out at a threshold point.) There’s no need to vary the system supply voltage to perform this adjustment. Instead, disconnect R1 from VCC and connect it to an accurate reference. Then, at 4.5V, adjust R4 until LED #1 just barely turns on. There is a slight interaction caused by the finite resistance (10k, type) of the LM3914’s voltage divider, so that repeating the above procedure once is advised. The LED driver outputs can directly drive a TTL gate, so that the LED #1 and LED #10 outputs may be used for under voltage and overvoltage warning signals. These may be used to initiate a soft shutdown or summon an operator, for example. The 470Ω resistor R8 ensures that the LM3914 output will saturate to provide the proper TTL low level. Pull-up resistor R9 provides the logic high level.

Remote Control Circuit Using KT3170

This circuit is which enables switching ‘on’ and ‘off’ of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls. The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit ‘0’ in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation. The circuit uses IC KT3170 (DTMF-to-BCD converter), 74154 (4-to-16-line demulti-plexer), and five CD4013 (D flip-flop) ICs.


The working of the circuit is as follows. Once a call is established (after hearing ring-back tone), dial ‘0’ in DTMF mode. IC1 decodes this as ‘1010,’ which is further demulti-plexed by IC2 as output O10 (at pin 11) of IC2 (74154). The active low output of IC2, after inversion by an inverter gate of IC3 (CD4049), becomes logic 1. This is used to toggle flip-flop-1 (F/F-1) and relay RL1 is energized. Relay RL1 has two changeover contacts, RL1(a) and RL1(b). The energized RL1(a) contacts provide a 220-ohm loop across the telephone line while RL1(b) contacts inject a 10kHz tone on the line, which indicates to the caller that appliance mode has been selected. The 220-ohm loop on telephone line disconnects the ringer from the telephone line in the exchange. The line is now connected for appliance mode of operation. If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues and the telephone can be used for normal conversation. After selection of the appliance mode of operation, if digit ‘1’ is dialed, it is decoded by IC1 and its output is ‘0001’. This BCD code is then demulti-plexed by 4-to-16-line demulti-plexer IC2 whose corresponding output, after inversion by a CD4049 inverter gate, goes to logic 1 state. This pulse toggles the corresponding flip-flop to alternate state. The flip-flop output is used to drive a relay (RL2) which can switch on or switch off the appliance connected through its contacts. By dialing other digits in a similar way, other appliances can also be switched ‘on’ or ‘off’.

Once the switching operation is over, the 220-ohm loop resistance and 10kHz tone needs to be removed from the telephone line. To achieve this, digit ‘0’ (in DTMF mode) is dialed again to toggle flip-flop-1 to de-energize relay RL1, which terminates the loop on line and the 10kHz tone is also disconnected. The telephone line is thus again set free to receive normal calls. This circuit is to be connected in parallel to the telephone instrument

Simple Remote Doorbell Warning Switch Circuit

This circuit should only be used with the solenoid type chime doorbells, the electronic type that play tunes will not work here. This is the simple circuit design.


The basic principle work is the hardest part for this circuit was the title. It is quite easy to miss the sound of a doorbell if you are watching the television, this circuit gets round the problem by providing a visual indication, i.e. a lamp. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from the doorbell batteries or transformer.

Using a series resistor R1 actually reduces current flow, and if run from batteries, will give them a longer life. The value of R1 is chosen so that about 0.6 to 0.7 volts is dropped across it, and the doorbell should still ring. I used a combination of a 22 ohm resistor in parallel with a 50 ohm. The doorbell still rang and circuit operated correctly. I used to have an electromechanical counter that registered each time when someone pressed the switch.

Ultrasonic Radar Circuit

This circuit named ultrasonic radar, where this circuit can in applying at security system house and or other security and safety system. in principle this circuit consisted of transmitter and receiver which transmitter and receiver can work with the same frequency, if both having different frequency hence this circuit cannot work. For circuit transmitter is given in symbol T, which frequency yielded by two NAND gates, causing yields signal multi vibrator, this signal which will be sent by transmitter then bound signal from transmitter in comparing to signal which in yielding by receiver, at receiver in symbol R. which entering signal strengthened by TR3 and strengthened again by IC OP-Amp 741. The signal from Op-Amp then returned by IC 2 here signal compared to which then is sent to which NAND gate if happened difference of frequency hence will activate TR1 and TR2 for in attributing to siren or indicator lamp.

LM317 Using to Power Supply and Audio Amplifier Circuit

This circuit in the figure is designed to help if you must transfer dc power and audio over a pair of copper wires. One application for such a circuit is a low-cost door-opening system with speech input. The circuit uses only one IC, the well known LM317, a low-cost power supply regulator. Using this chip, you can modulate the adjustment-pin input with the audio signal from an electrets condenser microphone, connected between the output and the adjustment terminals of the IC. The LM317 regulates the output in such a way that the voltage on the microphone is always 1.25V dc.


This circuit uses a WM34 electrets microphone, which comes in a standard 10-mm capsule from Panasonic and is common in low-cost equipment. You can use nearly any electrets capsule, because the well-regulated voltage on the microphone never exceeds 1.25V.

The principle work is every electrets capsule contains an integrated JFET based impedance converter that translates speech into a current flowing from the source to the drain terminal. This current through the microphone modulates the voltage on the variable resistor, RP. Because the output of the LM317 must follow the voltage on RP, you obtain a low-impedance audio signal riding on the output dc voltage. The microphone directly modulates the adjustment pin, so a smoothing capacitor, such as C1, for noise and hum does not influence the level of the audio signal. C1 shunts some of the audio signal to ground, but the LM317 compensates for the loss with internal gain. To avoid excessive losses in the LM317, use a capacitor with as low a value as possible. The circuit works well without a capacitor, but values as high as 47F do not present a problem. Using RP, you can adjust the dc output voltage and the gain for the microphone signal. For proper operation, the LM317 needs to deliver a minimum current of 4 mA from its output terminal. If your design uses no loudspeaker, you can connect a load resistor to sink this 4 mA. Designs using low-impedance loudspeakers must also have load resistors. You must add the ac current in the audio signal to the minimum current requirement of 4 mA. For an 8 loudspeaker, you need a minimum resistive load of 470_ to avoid distortion.

Simple Ni-Cad Battery Charger

This simple charger circuit uses a single transistor as a constant current source. The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base-emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. The charging current is approximately 15mA or 45mA with the switch closed. This suits most 1.5V and 9V rechargeable batteries.


The principle work of the charger is between one batteries with other battery dissociated by packer wall which there is in battery box, mean every space at battery doesn't correlate in consequence electrolyte fluid at every battery nor correlates (partition wall between batteries there shall no which leak).

In one batteries there is arrangement of plate that is some plates for positive pole (between plates dissociated by timber, ebonite or plastics, depends on technology applied) and some plates for negativity pole. Active agent from positive plate made from chocolate tin oxide (PbO2) while active agent from negativity plate is tin (Lead) pore (like sponge). The plates soaked by electrolyte fluid that is sulfate acid (H2SO4).

LM1458 Using for Variable Amp Power Supply

This regulated power supply circuit can be adjusted from 3 to 25 volt and is current limited to 2 amps as shown, but may be increased to 3 amps or more by selecting a smaller current sense resistor (0.3 ohm). The 2N3055 and 2N3053 transistors should be mounted on suitable heat sinks and the current sense resistor should be rated at 3 watts or more. Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. The Figure is shown in below;


The 1458 may be substituted in the circuit below, but it is recommended the supply voltage to pin 8 be limited to 30 VDC, which can be accomplished by adding a 6.2 volt zener or 5.1 K resistor in series with pin 8. The maximum DC supply voltage for the 1458 and 1558 is 36 and 44 respectively. The power transformer should be capable of the desired current while maintaining an input voltage at least 4 volts higher than the desired output, but not exceeding the maximum supply voltage of the op-amp under minimal load conditions. The power transformer shown is a center tapped 25.2 volt AC / 2 amp unit that will provide regulated outputs of 24 volts at 0.7 amps, 15 volts at 2 amps, or 6 volts at 3 amps. The 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt position.

LM339 Using for LED VU Meter

This circuit in below uses two quad voltage comparator using IC LM339 to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 mili volts or about 22 mili watt peaks in an 8 ohm system.


The divider voltages are set so that each LED represents about twice the power level as the one before so the scale extends from 22 mili watts to about 2.5 watts when all LEDs are lit. The sensitivity can be decreased with the input control to read higher levels. I have not built or tested this circuit, so please let me know if you have problems getting it working. This is the power levels should be as follows:
· 1 LED = 22mW
· 2 LEDs = 42mW
· 3 LEDs = 90mW
· 4 LEDs = 175mW
· 5 LEDs = 320mW
· 6 LEDs = 650mW
· 7 LEDs = 1.2 Watts
· 8 LEDs = 2.5 watts

Generating Long Time Delay Circuit

This design circuit of several hours can be accomplished by using a low frequency oscillator and a binary counter as shown below. A single Schmitt Trigger inverter stage (1/6 of 74HC14) is used as a square wave oscillator to produce a low frequency of about 0.5 Hertz. The 10K resistor in series with the input (pin 1) reduces the capacitor discharge current through the inverter input internal protection diodes if the circuit is suddenly disconnected from the supply. This resistor may not be needed but is a good idea to use.


The basic principle is the frequency divided by two at each successive stage of the 12 stage binary counter (CD4040) which yields about 1 hour of time before the final stage (Q12) switches to a high state. Longer or shorter times can be obtained by adjusting the oscillator frequency or using different RC values. Each successive stage changes state when the preceding stage switches to a low state (0 volts), thus the frequency at each stage is one half the frequency of the stage before. Waveform diagrams are shown for the last 3 stages. To begin the delay cycle, the counter can be reset to zero by momentarily connecting the reset line (pin 11) to the positive supply. Timing accuracy will not be as good as with a crystal oscillator and may only be around 1 or 2% depending on the stability of the oscillator capacitor.

Phototransistor for High Impedance Voltmeter

This circuit is designed to provide an inexpensive way to create a High Impedance Voltmeter while making use of an inexpensive analog or digital multi meter. The circuit is specifically designed for testing phototransistors. This the figure for the circuit;


When measuring voltages in high resistance circuits the resistance of the voltmeter itself has an effect on the circuit. For example if the voltage across a 1 Mega ohm resistor is measured with a voltmeter that has an internal resistance of 1 Mega ohm then the total resistance in that part of the circuit is effectively halved (two 1 M resistors in parallel = 500K ohms). In another example; If a voltmeter with a 1 Mega ohm resistance is placed in series with a 1 Mega ohm resistance there will in effect be two - 1 Mega ohm resistances in series, the resistor in the circuit and the resistance of the voltmeter. Under these conditions the maximum voltage that the voltmeter could show would be 1/2 of the supply voltage.

This is the principle work of the circuit. Phototransistors, when used to detect a train position essentially have two states of conductance. When the phototransistor is dark it has LOW conductance and the voltage across it will be HIGH if the phototransistor is has either visible or infrared light falling on it then its conductance will be HIGH and the voltage across it will be LOW. If the high impedance voltmeter circuit is used to measure the voltage across the phototransistor when it is dark it will not load down the circuit and should indicate almost 100 percent of the supply voltage.

Automatic Batteray Charger

This circuit basically is consisted of a comparator, that monitors reference tension which permanent. If battery tension exceeds maximum level which has in determining before all, relay would be active and will stop charging current. If battery tension went down under its low threshold value, relay is discharged causing enables reenter charging current.


Comparator formed by operation amplifier IC 741. Power allowance tension for amplifier Opamp stabilized by R8 and D4, so that is not influenced by stress variation of battery. Reference tension for operational amplifier alighted from power allowance is stabilized this through R7 and D3. Reference tension compared to a part of battery tension, what taken away from voltage divider R9/R10/R11.

For tuning of tension at R10 enters don’t tumble operational amplifier will become height, makes Q1 and Q2 on, causing activates relay and breaks current pegisian to battery. This aflame LED indicates that battery has been full loaded. To prevent battery connected returns to admission filling if there is the voltage drop a few, hence some of output tensions of operation amplifier is baited to input don’t tumble through R5 and R6. So thereby the operational amplifier is functioning equal to schmitt.