Telephone Auto Record Circuit: Set the recorder to the record position and when the telephone is taken off the hook, the recorder starts to record everything.

Black Market Press

TELEPHONE AUTO RECORD


This circuit requires neither a battery nor an AC supply to make it work. Set the recorder to the record position and when the telephone is taken off the hook, the recorder starts to record everything. When the phone is on the hook, the voltage across the phone lines is about 48 Vdc. When it is taken off the hook, the line voltage drops below 10 V. When the line voltage is near 48 V, the FET is biased off and no current can flow through Q2 and Q3. When the receiver is off the hook, the voltage drops, and allows Q1 to conduct. This action turns on Q2, Q3, and the cassette recorder.

Schematic: click below to enlarge

This is the schematic of the Phone Hold Button

Parts:

Part
Total Qty.
Description
Substitutions
R1 1 10M 1/4 W Resistor
R2 1 10M 1/4W Resistor
R3 1 22M 1/4W Resistor  
R4 1 39K 1/4W Resistor
Q1 1 2N4360 NPN Transistor  
Q2 1 2N2222 NPN Transistor
Q3 1 2N2102 NPN Transistor
C1 1 0.05 F Capacitor
C2 1 0.01 F Capacitor
T1 1  
MISC 1 Wire, Board, Case (If Used)

 

Notes:

  • Even though this is a simple circuit, you may have to check with your phone company before use.

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Telephone Auto Record Circuit: Set the recorder to the record position and when the telephone is taken off the hook, the recorder starts to record everything.