RUNNING MESSAGE DISPLAY

Light emitting diodes are advantageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED...

TELEPHONE CALL METER USING CALCULATOR AND COB

In this circuit, a simple calculator, in conjunction with a COB (chip-onboard) from an analogue quartz clock, is used to make a telephone call meter. The calculator enables conversion of STD/...

PARALLEL TELEPHONE WITH SECRECY

Often a need arises for connection of two telephone instruments in parallel to one line. But it creates quite a few problems in their proper performance, such as over loading and...

AUTOMATIC ROOM POWER CONTROLLER

An ordinary automatic room power control circuit has only one light sensor. So when a person enters,the room it gets one pulse and the lights come ‘on.’ When the person goes...

PROTECTION FOR YOUR ELECTRICAL APPLIANCES

Here is a very low-cost circuit to save your electrically operated appliances, such as TV, tape recorder, refrigerator, and other instruments during sudden tripping and resumption of mains supply. Appliances like...

TELEPHONE RINGER USING TIMER ICS

Using modulated rectangular waves of different time periods, the circuit presented here produces ringing tones similar to those produced by a telephone. The circuit requires four astable multivibrators for its working. Therefore...

TELECOM HEADSET

A compact, inexpensive and low component count telecom head-set can be constructed using two readily available transistors and a few other electronic components. This circuit is very useful for hands-free operation...

PRECISION 1HZ CLOCK GENERATOR USING CHIP- ON – BOARD

Usually the circuits for generation of 1Hz clock for applications in digital clock and counter circuits make use of ICs in conjunction with a crystal and trimmer capacitors, etc. However, similar...

ULTRASONIC PROXIMITY DETECTOR

We the humans can hear sound of up to 20kHz frequency only. This proximity detector works at a frequency of 40 kHz. It uses two specially made ultrasonic transducers: One transducer...

SECRET BELL

Many people move through the corridors and steps in multistoried buildings. As most of them are strangers for the inhabitants of the flats, it becomes necessary to verify the identity of...