Telephone status monitor


Posted on Jul 16, 2012

The LED indicates the status of a remote telephone. The light is off if the phone is hung up. It shines steadily if the phone is off hook, and it flashes on and off while phone rings and for 5 seconds after ringing stops. The flashing oscillator operates continuously but can drive the LED only when a ringing signal discharges the one shot capacitor to enable NAND gate G3


Telephone status monitor
Click here to download the full size of the above Circuit.

Thus, one oscillator handles several phone lines.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Interfacing seven segment to microcontroller
Full-wave scr control
PlayPIC
how to make automatic vehicle headlight
nimh battery problems and cures
simple analog comparator
Amplifier Circuit Output Relay Delay Audio
3A adjustable regulator using LM350
Low noise microphone amplifier circuit
single-813 crystal oscillator transmitter
555 electronic circuit diagram of a Christmas tree



Top