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Multivibrator Telephone Ringing Detector Circuit

2016-02-07 15:24  
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A telephone ring detector circuit is provided which finds particular utility in telephone answering systems. The detector circuit responds only to ring signals on the telephone line to activate the system, and it is unresponsive to dialing pulses, or other signals, that may be present on the telephone line. With the 555 timer connected as a multivibrator and an opto-isolator,a remote speaker can be driven.The detector circuit of the invention distinguishes the ring signals from the other signals on the telephone line by counting the number of pulses present on the telephone line for the various signals and providing a ring detect output only when the number of pulses is in excess, for example, of the pulses which form the trains of the dialing signal.
 
Telephone ringing detector