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Oscillator Remote Telephone Status Monitor Circuit

2015-01-25 04:25  
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A telephone status monitor circuit for determining the on/hook and off/hook conditions of a telephone connected across standard tip and ring terminals of a telephone system. The telephone status monitor circuit includes a charging circuit, in the form of a series combination of a capacitor and a resistor, which is adapted to be alternately and periodically switched in and out of circuit with the tip and ring terminals.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.Thus, one oscillator handles several phone lines.A telephone status monitor apparatus for determining the on/hook and off/hook conditions of a telephone connected across tip and ring terminals across which a ringing voltage may be present and superimposed on normal on/hook and off/hook voltages.
 

Telephone status monitor