Telephone-controlled tape starter

Posted on Feb 25, 2013

This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and Q2, will turn on and start the tape recorder. To turn the transistors off, and thereby stop the machine, apply a negative voltage to the base of Ql from the phone line

Telephone-controlled tape starter
Click here to download the full size of the above Circuit.

When the telephone receiver is on the hook, there is typically about 50 volts dc across the phone divided across Rl, R2, and R4 in such a way that the base of Ql is sufficiently negative to keep the tape recorder off. When the phone"s receiver is picked up, the voltage on the telephone line drops to about 5 volts, which leaves-insufficient negative voltage on the base of Ql to keep it cut off, so the tape recorder starts and begins to record.

Leave Comment

characters left:

New Circuits



Popular Circuits

Transformerless PSU
Scientific Calculator Watch
Sounds from the IC IT82207
op amp Trouble transferring schematic (working) to actual circuit (not working)
arduino scanning backlight
Tablet Reminder Uses Watch Module
Two channel audio mixer circuit design electronic project
Touch Controlled Musical Door Bell
Build a FM radio transmitter
1997 Buick Century the headlight relay
The EC10 communications receiver
DIY ECG Machine On The Cheap
The basic form of frequency equalization circuit
UPC1651 FM wireless microphone circuit