Doorphone Intercom

The circuit provides a simple illustration of a door phone intercom system having a two-way communication using the features of LM386 amplifier.The door phone circuit consists of speakers rated at 8 ohms that is used as an output speaker and as a microphone.

Telephone Amplifier

While talking to a distant sub scriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here.

Telephone Number Display

The given circuit, when connected in parallel to a telephone, dis- plays the number dialled from the telephone set using the DTMF mode. This circuit can also show the number dialled from the phone of the called party.

Phone Broadcaster

Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier.

Telephone call meter using calculator and COB

In this circuit, a simple calculator, in conjunction with a COB (chip-on-board) from an analogue quartz clock, is used to make a telephone call meter. The calculator enables conversion of STD and ISD calls to local call equivalents and always displays current local call-meter reading.

Telephone Message Watchdog

The Telephone Message Watchdog is an H8S/2398-based message-forwarding system for home telephones. The touch-tone detection system triggers when your answering machine picks up a call. After the caller hangs up, the system contacts you on your cell phone or pager.

Hamcom / JV Fax Interface

How to avoid radio interference to audio equipment and telephone

Isolated Telephone Interface

Isolated Telephone Interface

This circuit allows you to record audio from a telephone line into a tape recorder or computer soundcard. Most of the parts for this circuit can be scrounged from an old modem, with some work, it is possible to rewire the modem circuitry and use the old modem case.