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Telephone Bell Simulator Circuit

2016-02-12 17:32  
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The basic concept of a telephone line simulator is to allow phones, modems, fax machines, etc. to connect to a simulated telephone line which allows the connected devices to "think" they are plugged into a real telephone jack that goes to the phone company's central office.This circuit is intended for use in a small private telephone installation. The ringing tone sequence is 400 ms on, 200 ms off, 400 ms on, 2 ms off. In the accompanying diagram, N1 and N2 form an oscillator that operates at a frequency of 5 Hz, which gives a period of 200 ms. The oscillator signal is fed to two decade scalers, which are connected in such a manner (by N3 and N4) that the input signal is divided by 15. The second input of N4 can be used to switch the divider on and off by logic levels.If this facility is not-used, the two inputs of N4 should be interconnected.The better Simulators have real (precision) signals for dial tone, busy signal, ring-back tone, re-order tone, ringer current, etc.  They also work with touch-tone dialing or rotary dialing and each phone port can be programmed with any phone number of one to 16 digits.  Many (such as mine) have an audio port for monitory calls or playing prerecorded messages plus the ability for conference calling, call transfer, etc. 

Telephone Bell Simulator Circuit