Telephone line monitor

This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less.

• R1 270K 1/4 W Resistor
• R2 1.5K 1/4 W Resistor
• R3 68K 1/4 W Resistor
• R4 33K 1/4 W Resistor
• C1 0.22uF 150 Volt Capacitor
• Q1, Q2 2N4954 NPN Transistor
• D1 1N645 Diode
• MISC Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug