Circuit lab, Diagrams,Free circuits, Electronics periodical, Design: India

.	S E C T I O N S

Registered Users

New User?

Forgot Password?

Benefits for registered users
1.	Free access to latest circuits in Circuit Lab
2.	Free submission of your website(s)
3.	Free submission of events
4.	Can submit queries in Bulletin Board
5.	Can submit articles or weblinks in Technical Articles

Latest Issues

April 2026

Tell me more

Subscribe print version

Renew print version

Subscribe digital version

C I R C U I T L A B

Click to view in order of 'highest hits first'

Vibration-Activated Smart CRO Probe (New)

Here is a simple, low-cost, energy-saving and device-saving circuit for an electronics lab, service centre, electronics workshop, or wherever a CRO is in use.

Infrared Sensor Based Power Saver (New)

The simple circuit presented here will automatically switch off electrical appliances like lights or fans as you vacate a room, after a predetermined time period.

4-Channel Multi-mode Audio Amplifier (New)

Sometimes we need configurable multichannel amplifiers for experiments or for use in offices or schools. Here is a circuit based on TDA1554Q, configured for multi-mode function with four channel outputs.

Power Bank for Smartphones (New)

This power bank can be used for charging smartphones. The circuit uses two integrated modules and a lithium-ion battery. The first module is a lithium-ion battery charger and the second is a DC-DC boost converter module.

Infrared Motion-Sensing Relay Switch (New)

This circuit is designed for use with all kinds of medium-power automobile/domestic 12V DC loads. It is a simple solid-state relay (SSR) switch, controlled by a standard passive infrared (PIR) motion sensor module.

Illuminated Optical Magnifier

We often face problem while reading the values of ICs and miniature SMD components, detecting cracks or shorts in tracks in a PCB, or reading a finely-graduated vernier scale. Here is a solution to the problem in the form of a simple optical magnifier that simultaneously magnifies and illuminates the object.

Programmable On and Off Controller for 3-Phase Motor

Automatic on/off controller for a 3-phase electric motor can be made with a programmable time switch. In this case a maximum of eight time durations can be programmed.The system has two programmable time switches for setting the starting and stopping times of the motor and two control circuits, which are interfaced with the start and stop switches of the 3-phase motor’s starter.

Fire Alarm Using a Thermistor

This project can effectively be used as a temperature-sensing fire alarm. Here, an NTC thermistor is used as the temperature sensor. Resistance of the NTC thermistor decreases with an increase in temperature.

Automatic USB-Controlled Power Switch

Here we present a circuit that can control mains power of an LED TV and a DTH set-top box (STB).

Door-Opening Alarm Using Hall Sensor

This simple door-opening alarm uses a hall sensor to produce sound when someone opens the door. The circuit can be installed at a workshop, office or home for security purposes. The 3-terminal hall sensor is easily available in the market.

Device for Maintaining Car Batteries

When we do not drive our cars for extended periods of time, the abandoned rechargeable batteries become fully discharged. Sometimes, these get damaged, too. Presented here is the simple device that can maintain two 12V rechargeable batteries.

Over-Heat Detector

An NTC thermistor’s sensitivity to temperature changes, even in small increments, enables the device to be used in temperature-sensing/control applications. This project for the over-heat detector uses a 10k NTC thermistor.

Four Frequencies Generator

This circuit produces fixed frequencies of 4MHz, 6MHz, 10MHz and adjustable square-wave with variable frequencies from around 10Hz to more than 100kHz.

Dual Audio-Signal Tracer

The circuit described here is of a dual audio-signal tracer. An audio-signal tracer is a simple device used to troubleshoot for audio signals in radio and other electronic circuitry.

Simple Light and Sound Indicator for Mains Power Supply

While repairing or installing electrical machines in a building, the AC mains power supply is switched off from the mains electrical switchboard installed outside the building. There is a chance that someone who is not aware on the mains from outside. This poses a great danger for the technician working inside. Hence, an indicator like the one described here, which can be plugged into a nearby mains wall socket, might prove very useful for the technician.

Smoke, Alcohol and LPG-Detection Alarm

Presented here is a circuit for raising an alarm on detecting smoke or LPG cooking gas leakage, or even alcohol vapours in breath. This is achieved by using a basic unit with different sensors for smoke, LPG and alcohol. So, different alarms can be made by simply changing the input sensor.

Museum Watchdog

This self-contained alarm widget provides a flexible, cost-effective solution for museums, art galleries, historic houses, heritage properties and corporate offices, among others.

Wireless Baby Monitor

You can now monitor your sleeping baby with this wireless baby monitor. It is a radio system used to remotely listen to sounds made by an infant. Simply place the circuit near your sleeping baby and listen through an FM receiver from any other room in the house.

12V Battery Absorb and Float Charger

Most battery chargers stop charging the battery when it attains its maximum charging voltage set by the circuit. This circuit charges the battery at a particular voltage, that is, absorption voltage, and once the maximum charging voltage is attained, the charger changes the output voltage to float voltage for maintaining the battery at that voltage. Absorption and floating voltages are dependent on the type of battery.

Multichannel Visual Thermometer

Temperature of some electronic components used in a device may rise unexpectedly and these might get damaged. This multichannel visual thermometer can indicate the problem through glowing LEDs. Since transistors are very cheap and widely available, this circuit uses these as low-cost temperature sensors and amplifiers.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Next ›