TELEPHONE CALL RECORDER

Today telephone has become an integral part of our lives. It is the most widely used communication device in the world. Owing to its immense popularity and widespread use, there arises...

PYROELECTRIC FIRE ALARM

Here is an ultra-sensitive fire sensor that exploits the direct piezoelectric property of an ordinary piezo element to detect fire. The lead zirconate titanate crystals in the piezo element have the...

REMOTE-OPERATED MUSICAL BELL

This infrared light controlled 12-tone musical bell can be operated using any TV remote control. It can be operated from up to 10 metres, provided the remote control is directed towards...

MINI UPS SYSTEM

This circuit provides an uninterrupted power supply (UPS) to operate 12V, 9V and 5V DC-powered instruments at up to 1A current. The backup battery takes up the load without spikes or...

DUO PHONE

This simple circuit of a duophone allows you to access two telephone lines through one telephone set. Each telephone conversation will remain entirely separate unless you choose to combine the two...

Smart Loop Burglar Alarm

Simple loop burglar alarms sound whenever the loop breaks. What if a clever thief comes to know of the working of this alarm? He may simply short the loop by using...

CAR-REVERSING HORN WITH FLASHER

Here is a simple circuit that starts playing the car horn whenever your car is in reverse gear. The circuit (refer Fig. 1) employs dual timer NE556 to generate the sound....

Stereo Headphone Amplifier

Here is an inexpensive circuit for a stereo amplifier to drive a low-impedance headphone set. The circuit uses a few cheap transistors (BC547 and BC557) and passive components like resistors, diodes...

Whisker for Robots

Whiskers for robots are simple switch-type sensors that work like an animal’s whiskers detecting nearby objects in the environment. When disturbed, the sensor sends a pulse to the robot to indicate...

TRANSISTORISED LOGIC PROBE FOR TTL

A logic probe is a handheld pen-like probe used for analysing and troubleshooting the logical states '0' or '1' of a digital circuit. While most logic probes are powered by the...