DIY Telephone Call Meter Using Calculator and Quartz Clock Circuit
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...
Connect Two Telephones in Parallel Without Interference
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...
DIY Compact Telecom Headset Circuit for Hands-Free Communication
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...
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...
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...
Build a High-Quality Dual Power Supply for Audio Amplifiers
High-quality audio amplifiers require a very efficient power supply with negligible ripple, hum and buzz. An ordinary bridge-type power supply has a drawback in...
Variable Power Supply Using a Fixed-Voltage Regulator IC
A voltage regulator (also called a ‘regulator’) with only three terminals appears to be a simple device, but it is in fact a very...