Telephone line monitoring circuit


This is very useful circuit for all because you can record telephone conversations automatically.What you have to do is connecting this unit to the phone line,Recorders remote control jack and to your tape recorder's microphone input.when the voltage of the line drops 5v or less it automatically starts to record.





Parts

R2 1.5K 1/4 W Resistor

R4 33K 1/4 W Resistor
C1 0.22uF 150 Volt Capacitor
R1 270K 1/4 W Resistor
Q1, Q2 2N4954 NPN Transistor
D1 1N645 Diode
R3 68K 1/4 W Resistor
MISC Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug

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