RLC Resonance Circuit

 At low frequencies, L1 looks like a short circuit, and C1 looks like an open circuit, so V(in) and V(out) are closely linked by R1. At high frequencies, L1 looks like an open circuit and C1 looks like a short circuit, so V(out) approaches zero. But in the middle range of frequencies, something interesting happens. In fact, for a narrow range of frequencies around 1MHz, this circuit actually produces a tremendous amount of voltage amplification!

 

Thermostat Temperature Sensor Schematic

This is a sensor that design type electro-mechanical temperature sensor or switch, that basically consists of two different metals such as nickel, copper, tungsten or aluminium etc, that are bonded together to form a Bi-metallic strip. The thermostat can be used itself as an electrical switch or as a mechanical way of operating an electrical switch in thermostatic controls and are used extensively to control hot water heating elements in boilers, furnaces, hot water storage tanks as well as in vehicle radiator cooling systems. This is a figure schematic for the sensor.

TLP310xA - High Current Photo Relays

This is relay that produce by Toshiba corporation. This is new high current photo relays that have 3 types. They are called TLP3106A, TLP3107A and TLP3109A. These devices have an off-state output terminal voltage ranging from 30-100V and a steady on-state current of 3.0 to 4.5A in a small 2.54SOP6 package for factory automation and industrial applications. This is the figure of the relays.

Dog Repellent Ultrasonic Circuit

This is a design circuit for Dog Repellent Circuit Schematic diagram. When we hear the word “Ultrasonic" we often refer it to bats and dolphins communication. Technically, “Ultrasonic" applies to sound that is anything above the frequencies of audible sound, and includes anything over 20kHz. Frequencies used for medical diagnostic ultrasound scans extend to 10 MHz and beyond. This dog repellent ultrasonic circuit will chase away angry dogs. It comprises of a 555 timer IC, a speaker/piezoelectric and a little ferrite transformer. This is the schematic diagram.

Security Light & Switch Circuit Using PIR Sensor

This is a design circuit for security light and switch circuit using PIR Sensor. SB0061 is a pyroelectric sensor module,developed for human body detection. A PIR detector combined with a fresnel lens are mounted on a compact size PCB together with an analog IC (SB0061) and limited components to form the module. High level output (3.3V) of pre-settable variable width (5Secs -18 Minutes) is provided. This is the figure of the circuit;

Circuit diagram of the PIR Motion Sensor Light and Switch based on SB0061 shown here can be used for security or corridor lighting in power saving mode. The 12V DC supply required for the whole circuit can be fed from any standard 12V ac mains adaptor/battery.

Working of the circuit is simple and straight forward. When any movement is detected within near 5-6 metres, around 3.3 Volt is appeared at the base of Transistor T1 and it conducts to fire the next relay driver transistor T2. As a result, the 12V DPDT relay is energised to power the White LED through current limiting resistor R3. Spare relay contacts can be used as a switch to control any suitable external load. The white LED and the relay remains ON for a duration based on the mono time setting in SB0061, ie from 5 Secs to 18 Minutes.

Line Following Robot Sensor

Here’s a design circuit for Line Following Robot sensor or surface scanner for robots is a very simple, stamp-sized, short range (5-10mm) Infrared proximity detector wired around a standard reflective opto-sensor CNY70(IC1). This is the figure of the circuit;

How this circuit can work? IC1 contains an infrared LED and a phototransistor. The LED emit invisible infrared light on the track and the phototransistor works as a receiver. Usually, black colored surface reflects less light than white surface and more current will flow through the phototransistor when it is above a white surface. When a reflection is detected (IR light falls on the phototransistor) a current flows through R2 to ground which generates a voltage drop at the base of T1 to make it conduct. As a result, transistor T2 start conducting and the visual indicator LED(D1) lights up. Capacitor C2 works as a mini buffer. After construction and installation, the scanner needs to be calibrated. Initially set P1 to its mechanical centre position and place the robot above the white portion of the track.

Now slowly turn P1 to get a good response from D1. After this, fine tune P1 to reduce false detection caused by external light sources. Also ensure that the LED remains in off condition when the sensor module is on the black area. Repeat the process until the correct calibration is achieved. The red color LED (D1) is only a visual indicator. You can add a suitable (5V) reed relay in parallel with D1-R4 wiring after suitable alterations to brake/stop/redirect the robot. Similarly, the High to low (H-L) transition at the collector of T2 can be used as a signal to control the logic blocks of the robot. Resistor R1 determines the operating current of the IRLED inside IC1. The sensing ability largely depends on the reflective properties of the markings on the track and the strength of the light output from IC1.

Motion Sensor Switch Circuit for Alarm

Here’s a design circuit for motion sensor switch circuit is a motion sensor controlled automatic water sprinkler but you can easily add an alarm/light function too. Before beginning the construction contact your nearest electronics component vendor and procure a readymade box-type Passive Infrared (PIR) Motion Sensor unit. Such units, packed in a compact enclosure with power input and relay output terminals are widely available. Here’s the figure of the circuit;

Now install the PIR module hanging from a 3 meter high mast (to cover 10 meter radius area) and connect its supply and relay terminals to our finished and enclosed circuit, observing right polarity. A 4-core screened cable can be used for this interconnection. Power the circuit from a regulated 12VDC adaptor/solar power box.

Whenever the PIR module detect movement of a live body its relay output toggles and the switching mosfet (T1) in the circuit is switched to on via resistor R1 and related parts. As result, the EM relay at the output of T1 is activated and the electric sprinkler gets its supply through the relay (RLY1) contacts. This contacts (or spare contacts) can also be used to activate a high-power warning alarm.

Missing Pulse Detector Circuit Using 555 IC

This is a design circuit for missing pulse detector will receive a source of repetitive pulse in normal condition. The output of this detector circuit will be inactive for normal condition (output pin 3 of  555  IC will be high, turning off the LED indication). If now the input pulse is missing, delayed, or stopped, then the output of this detector circuit will be active, giving an indication that the condition is abnormal by turning on the LED. Here’s the figure of the circuit; 

The period of no-pulse condition can be adjusted by changing 0,1uF capacitor. This circuit assume that active condition is low, and inactive is high. This assumption applied for both input and output. When the input is actively switched between high and low, the capacitor will be alternately charged toward +10V and discharged to ground. In normal condition, fast discharging will make the capacitor voltage never reach the triggering level of 555 IC. If the input pulse disappears of delayed, which means the input is tied to high voltage for certain period, then the charging of capacitor will reach the triggering level of the IC (2/3 Vcc) and activate the indicator.

Ultrasonic Motion Detector Circuit

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.

9 Sec Timer Using LED Indication And Control Relay Circuit

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

Battery Level Indicator Circuit

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]

Heating Circuit System for Thermostat

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

Logic Probe with Pulse Indicator Circuit

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.

Water Level Sensor Circuit Using LM1830 Single Chip

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

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].

Current Loop Transmitter Circuit for Temperature Sensor

This circuit provide current loop transmitter for temperature sensor. Current loop interface has been widely used in industrial environment because it’s robustness. This is the figure of the circuit.


The temperature measurement is done by LM35 temperature sensor chip. You can use general silicone diode such as 1N4001. The current controller function is done by LM317 current/voltage regulator. This circuit will draw a consistent current proportional to the temperature being measured, regardless the supply voltage variation caused by noise or long wire’s temperature-dependent resistance variation.

Swimming Pool Solar Heat Control Circuit

This is a swimming pool solar heating panel pump control. The circuit in below is use an external thermistor that is attached to the solar panel in a manner that will allow it to sense heat generated by direct exposure to the sun. This circuit is controlled by IC TC621-C. This is the figure of the circuit.


A thermistor with a resistance of about 100 kΩ at 25°C should be selected. One such thermistor is the ACW-027 from Ketema, which can be clamped around a pipe in the solar panel. This circuit will energize the pump when the sun is heating the panels and turn off the pump when the sky is cloudy or the sun goes down. To prevent rapid cycling of the pump during partly cloudy conditions, the hysteresis is set for a relatively wide (20°F) span. Providing low thermal impedance between the thermistor assembly and the solar panel will also prevent rapid pump cycling by adding the solar panel’s thermal time constant to the hysteresis. To select the set point resistors, consult the thermistor data sheet for the thermistor’s value at the desired temperature. For example, assume that we want the pump to turn on (high set point) at 100°F and turn off (low set point) at 80°F. [Schematic diagram source: Microchip Technology, Inc].

Baxandall Tone Control Circuits Using Two Transistor

This is design circuit of tone control circuit that is use very popular Baxandall configuration, a simple circuit configuration that provides boost and cut control in continuous manner. This circuit is very cheap to build, and it’s commonly implemented in commercial product. This circuit is built by two transistors. This is the figure of the schematic.


The transistors can be substituted by any general audio transistors with small current gain more than 100 (BC547, 2N3904, and many more). The supply voltage for this circuit is 9-15V DC. The components that is used is low cost and can buy in component electronics store.

Dual Channel Digital Volume Control Circuit

This is a design for digital volume control. This circuit could be used for replacing your manual volume control in a stereo amplifier. This circuit is built from 7555, 74193 and dual 4066 IC. This circuit is a dual channel volume control. This is the figure of the circuit.


IC1 timer 555 is configured as an un-stable 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 active high outputs A, B, C and D of the counter are used for controlling two quad bi-polar analogue switches in each of the two CD4066 ICs (IC3 and IC4). Each of the output bits, when high, short a part of the resistor network comprising series resistors R6 through R9 for one channel and R10 through R13 for the other channel, and thereby control the output of the audio signals being fed to the inputs of stereo amplifier.

Touch Switch Circuit

This is a touch circuit that is used as a latching circuit to switch a LED ON and OFF by physically touching the ON metal plate or OFF metal plate. This circuit is based on logic gate for control the operation. This is the figure of the circuit.


It is important to ensure that 9V battery is used as its DC source. If one uses the mains supply to step down the voltage using a transformer for rectification and filtering to get the 9V DC supply, ensure that the transformer is designed in such a way that it follows the safety standard requirement of UL. This is important to ensure the safety of the user that is using the metal contacts to ON/OFF the LED.[Schematic diagram source: Electronics Project Design].