Telephone In-Use Relay Controller
Telephone circuits

Telephone In-Use Relay Controller

By Bill Bowden


Circuit to close a relay when any phone extension is off-hook.

Telephone In-Use Relay Controller circuit
Telephone In-Use Relay Controller circuit

Voltage at the gate of the MOSFET should be negative (1-3 V) with respect to the source when phones are on-hook. Voltage at the gate should be positive (8-10 V) with respect to the source (ground) when any phone extension is off-hook. A high impedance meter is needed to measure the on-hook voltages accurately. Circuit should draw less than 5 uA from the phone line. Relay used is a 12 V DC / 120ohm coil, but most any small 12 V DC relay should work. Power supply regulation should be +/- 2 V.

1412 22 August 2007

See also:

9-pin null modem cable
9-pin to 9-pin female
Electronics Telephone Talking Circuit
This is the basis of electronics telephone sets.
Telephone Ring Generator Using Switching Supply
The telephone ring generator shown below generates the needed high voltage from a simple switching mode power supply.

лотерея гринкарт

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