The circuit presented here can be used for connecting two tele phones in parallel and also as a 2-line intercom. Usually a single telephone is...

The circuit as shown in the figure employs 14 bi-colour (red and green) LEDs having three terminals each. Different dancing colour patterns are produced...

Many a times one needs an extra telephone ringer in an adjoining room to know if there is an incoming call. For example, if...

Here’s a circuit to display the song number in an audio system for quick reference to songs. It also serves the purpose of an...

The circuit presented here can be used as a lock for important electronic/electrical appliances. When card is inserted inside its mechanism, depending upon the position...

The timer circuit described here provides a pleasant musical tone in your darkroom at 1-second intervals.The circuit takes up very little space and can...

Here’s a simple circuit of an electronic horn that is built around quadruple op-amp IC LM3900 (IC1). IC LM3900 has four independent op-amps (A1...

Here is a teleremote circuit which enables switching ‘on’ and ‘off’ of appliances through telephone lines. It can be used to switch appliances from...

Here is a sleep-switch circuit that can be easily converted into a wake-up timer. A dual-mode time setting makes the system versatile. The circuit...

Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes inoperative...