Wire Tracer (Receiver)

The circuit depicted is the receiver device of a transmitter/receiver combination that will prove extremely handy when tracing the path of electrical wiring in a building or to locate a break in a wire. The corresponding transmitter may be found elsewhere in this website. The transmitter produces a distinctive tone which alternates between 2100 Hz […]

Easy Loudspeaker Circuit For Telephone

This below circuit is a easy handsfree telephone receiver system. This doesn’t have dialing circuit so, it’s not a total phone replacement circuit, but it’s just only a loudspeaker system (i.e, phone receiver,not dialer). This is a easy circuit with all parts easily available, and without any complex I.C. It is made of just capacitors, […]

Phone In Use Indicator

With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause […]

Telephone In-Use Indicator Circuit

This circuit will illuminate a LED if one of your telephones is in use. It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC. Please note that it is illegal to make a physical permanent connection to your telephone line in some countries (this includes the UK […]

Electronic Telephone Ringer

This circuit produces a ringing sound similar to that made by more recent telephones. It consists of three almost identical oscillators connected in a chain, each generating a squarewave signal. The frequency of each oscillator depends on the RC combination: R4 and C1 around IC1.A, R8 and C2 around IC1.B and R12 and C3 around […]

Cheapskate’s Headset Adapter

Here’s a cheaper and easier method of making a telephone headset adapter. All that’s required is a cheap headset ($5 at Harvey Norman), a DPDT switch and a few connectors. Each transducer in the headset measures about 40O. There is also an inline volume control measuring about 500O per leg, across which each earphone is […]

Telephone Line Indicator

With the aid of an (old) moving coil instrument it is very little effort to make a simple voltmeter that, at a glance, indicates the status of a telephone line. Because the input impedance of this circuit is very high, there is no problem in having it permanently connected to the line, since it only […]

Telephone Free Indicator

Depending on local regulations and the telephone company you happen to be connected to, the voltage on a free telephone line can be anything between 42 and 60 volts. As it happens, that’s sufficient to make a diac conduct and act like a kind of zener diode maintaining a voltage of 38 V or so. […]

2-Line Intercom-Telephone Line Changeover Circuit

The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom. Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for connecting the other telephone. In this simple parallel line operation, the main […]

Simple Telephone Recorder

This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder’s microphone input, and the recorder’s remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less. R1 1 270K 1/4 W Resistor […]