Build a Telephone Conversation Recorder Circuit Diagram. This Telephone Conversation Recorder Circuit Diagram enables automatic switching-on of the tape recorder when
the handset is lifted. The tape recorder gets switched off when the
handset is replaced. The signals are suitably attenuated to a level at
which they can be recorded using the ‘MICIN’ socket of the tape
recorder.
Points X and Y in the circuit are connected to the telephone lines.
Resistors R1 and R2 act as a voltage divider. The voltage appearing
across R2 is fed to the ‘MIC-IN’ socket of the tape recorder. The values
of R1 and R2 may be changed depending on the input impedance of the
tape recorder’s ‘MIC-IN’ terminals. Capacitor C1 is used for blocking
the flow of DC.
The second part of the circuit controls relay RL1, which is used to
switch on/off the tape recorder.
Telephone Conversation Recorder Circuit Diagram
A voltage of 48 volts appears across
the telephone lines in on-hook condition. This voltage drops to about 9
volts when the handset is lifted. Diodes D1 through D4 constitute a
bridge rectifier/polarity guard. This ensures that transistor T1 gets
voltage of proper polarity, irrespective of the polarity of the
telephone lines.
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