Posted on Jun 15, 2012

This recorder can be connected to the telephone lines just about any place, and no external power source is needed. The tape recorder`s switch terminals are applied to a pair of transistors, connected as Darlingtons, that are used to turn the recorder on and off. When the telephone is off-hook there`s usually about 50 Vdc across the phone that`s divided over Rl, R2, and R4, so that Ql`s base is negative enough to keep the recorder off.

Click here to download the full size of the above Circuit.

Pick up the receiver, and the voltage drops to 5 V. That leaves not quite-enough voltage on Ql"s base to keep that transistor at cutoff, so the recorder begins. Remember to keep your recorder"s switch in the on position, and depending on how many people use the telephone, remember to rewind or change tapes occasionally!

Leave Comment

characters left:

New Circuits



Popular Circuits

Pushpull Amp
60W Power Amplifier with 2N3055
Phone digital answering machine
cmos 4047 power inverter 12vdc
Door Entry Detection for MCU Based Designs
low cost high speed photography
embedded webserver.
RS 422 Compatible Indicator
Low Frequency Antennas
DAC0832 single - bipolar voltage output interface circuit