Automotive Circuits, Light Related

Automatic headlight dim switch.

Description. With this cool circuit integrated to your cars headlight system , you can drive cool headed in high beam.The circuit will take over the duty of low beaming the headlight when vehicles approach against , and high beams the lights when they pass over. The circuit is based on a photo transistor(Q1) for sensing […]

Home Circuits, Telephone Related

Telephone off-hook indicator

Description. The circuit depicted here can be used as an indicator when the telephone receiver is off-hook. The circuit can be in corporated with old telephones that does not have such an indicator. The circuit uses a complementary darling to pair using Q1 (2N3904)and Q2 (2n3906) to sense whether the receiver is off hook and

Radio Circuits, Radio Transmitters, Transmitters

FM Tracking transmitter

Description. The circuit presented her will transmit a audio tone in the FM  band. The circuit can be used as a tracking signal transmitter or a remote control transmitter. The circuit uses only easily available components and any one can build this. The transmitter has a range of 100m @ 9V supply, with a matching

Fire Alarm

Fire alarm using thermistor & NE555

Description. Many fire alarm circuits are presented here,but this time a new circuit using a thermistor and a timer to do the trick. The circuit is as simple and straight forward so that, it can be easily implemented. The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon

Home Circuits, Light Related, Lighting Circuits

Street light circuit.

Description. The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises. In fact you can this circuit for implementing any type of automatic night light. The circuit uses a Light Dependent Resistor (LDR) to sense the light .When there

Audio Circuits

Low cost amplifer.

Description. No big deal here! You can make a decent power amplifier using just three transistors. All components used here can be obtained from your electronic junk box. Also you just need a 9V transistor radio battery to power this circuit. The circuit is ideal for a pocket radio or other hand held audio equipments.

Fire Alarm, Security & Saftey

Fire alarm circuit

Description. Here is a simple fire alarm circuit based on a Light Dependent Resistor (LDR) and lamp pair for sensing the fire. The alarm works by sensing the smoke produced during fire. The circuit produces an audible alarm when the fire breaks out with smoke. When there is no smoke the light from the bulb

Power Supplies, Sensor Circuits

Mains failure alarm circuit

 Description. Here is a simple mains power failure alarm/detector circuit that produces an alarm whenever the mains supply fails. Lot of such circuits are available, but the peculiarity of this circuit is that it requires no back up power source like a battery to power the alarm when the mains is absent. When there is

Industrial Circuits, Sensor Circuits

Dew sensitive switch

Description. Here is a simple circuit that can be used to switch ON or OFF a device when the dew present in the surrounding atmosphere crosses a set value. The circuit uses a dew sensitive resistive element and a comparator based on LM 358 to perform the above said operation. At normal condition the resistance

Home Circuits, Power Supplies

High & Low voltage cut-off with delay& alarm

Description. This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used  to make a automatic

Automotive Circuits, Battery Circuits

Simple battery charger circuit

How to make a 12V battery charger at home? Description  Here is the circuit diagram of a simple and straight forward 12 V battery charger circuit with diagram. This circuit can be used to charge all type of 12V rechargeable batteries including car batteries. The circuit is nothing but a 12V DC power supply with

Oscillators, Test & Measurement Circuits

Saw tooth wave generator using NE555

Description. A simple sawtooth wave generator circuit for generating a saw tooth wave form using a NE555 IC is given below. The frequency of the wave form can be varied by using a POT. The capacitor C, resistor R and zener diode forms a constant current source for charging of the capacitor. When the voltage

Oscillators, Test & Measurement Circuits

Variable frequency oscillator

Description. Here is a simple variable frequency circuit based on timer NE555. Here NE55 is wired as an astable multivibrator, whose output frequency can be varied by varying a potentiometer. This circuit is a must in the work bench of a electronic hobbyist. Frequencies ranging from several Hz to several KHz can be obtained using

Audio Circuits, Transmitters

IR Headset

Description. Here is a simple IR headphone circuit that is suitable for listening to TV or radio with out disturbing others. For beginners the IR headset is a better option than FM head sets because they often produce desirable sound quality with out tuning as well as difficult impedance matching that is often done  in 

Power Supplies

9 V regulator using 7809

Description. Here is the circuit diagram of 9 V regulator using popular 7809 IC. The 7809 is a 9 Volt voltage regulator IC with features such as internal current limit, safe area protection, thermal protection etc. A 16 V transformer brings down the 230V mains, 1A bridge rectifier rectifies it and capacitor C1 filters it

Industrial Circuits, Test & Measurement Circuits

Humidity tester

Description. A variety of humidity tester circuits are available, but this  is a circuit which is as simple as possible. Using only a transistor, LED and few resistors, this circuit can be used to check the humidity level of materials like soil, paper etc. When the humidity in a substance increases the current conducted through 

Power Supplies

5V power supply using 7805.

Description. 7805 is a 5V fixed three terminal positive voltage regulator IC. The IC has features such as safe operating area protection, thermal shut down, internal current limiting which makes the IC very rugged. Output currents up to 1A can be drawn from the IC provided that there is a proper heat sink. A 9V

Motor Related

Stepper motor controller

Description. Here is the circuit diagram of a simple stepper motor controller using only elementary parts. The driver circuit uses, four transistor (SL100) to drive the motor windings, two NOT gates and one XOR gate to decode the two bit control logic to drive the four windings of the motor. The diodes D1 to D4

Radio Transmitters

Simplest FM Transmitter.

Description. Here is the circuit diagram of the simplest FM transmitter using a transistor. Great performance or range is not guaranteed here, because this is an elementary design. General purpose radio frequency transistor BF 494 (Q1) is used here for obtaining FM modulation. A condenser mic is used here to pickup the sound. The condenser

Industrial Circuits, Sensor Circuits

Digital temperature sensor

Description. Here is a straight forward, yet effective digital temperature controller that can be used with temperature control systems. The circuit uses IC LM 35 (IC3) to as the temperature sensor. The output of LM 35 is given to the IC ADC 0804 (IC4) which converts the analog output of the LM 35 to digital

Fun & Game Circuits, Tone generator circuits

UJT Organ circuit

Description. Here is the circuit diagram of a simple yet interesting mini organ based on UJT 2N 4891 (Q1). You can produce the desired sound by pressing each pushbuttons. You have also the option to set each push button to produce the desired tune you want. The circuit is based on a UJT oscillator who’s

Lighting Circuits

Air craft warning light circuit

Introduction. Here is low cost circuit that can be used for implementing a warning light on the top of tall structures as a warning for low flying aircrafts. Usually such lights are just stay glow type. Here our light is a flashing type, and surely this will draw more attention and of course add more

Home Circuits

Mosquito repeller power saver

Description. Almost all liquidator type mosquito repellers are rated 5Watts. It is a pretty energy consuming game  when these repellers are operated through out the night. Even though these liquidators are switched ON and OFF in discrete intervals there will be no considerable loss in the effectiveness, and more over there will be a great

Battery Circuits

Super fast Ni-Cd battery charger

Description. Here is  the circuit diagram of an effective and super fast Ni-Cd battery charger circuit.The circuit is based on the IC MAX 712. The circuit is designed to fast charge a Ni-Cd battery at 3oomA. After the fast charging is completed the circuit charges the battery in trickle charging mode at 15 mA. Here

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