Telephone Record Control
This circuit will allow you to connect any tape recorder that has a mic and
remote input to a phone line and automatically record both sides of a
conversation when ever the phone is 313i86d in use. You will need to take a
couple of voltage readings before connecting the circuit. First determine the
polarity of your phone line and connect it to the circuit as shown and then
determine the polarity of the remote input and connect it to the circuit.
Circuit operation is as follows. When the phone is on hook the voltage across
the phone line is about 48volts dc. When the phone is off hook the voltage will
drop to below 10volts dc. When the line voltage is at 48volts the FET is off
which causes Q2 and Q3 to be off. When the phone is picked up the FET turns on
along with Q2 and Q3 which turns your recorder on. The tape recorder must be in
the record mode at all times. As you can see the power source for the circuit
is the phone line.
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