WATCH-DOG FOR TELEPHONES
Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap misuse indications....
INTELLIGENT SWITCH
This intelligent switch circuit enables automatic, switching on of an emergency light system during darkness in the event of mains failure. The mains power...
LOW CURRENT, HIGH VOLTAGE POWER SUPPLY
A high voltage power supply is a very useful source which can be effectively used in many applications like biasing of gas-discharge tubes and...
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...
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...
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...
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...
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...
Telecom Headset
A compact, inexpensive and low component count telecom headset can be constructed using two readily available transistors and a few other electronic components. This...
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...
