Public telephone set

Details Public telephone set Public telephone set

1987-06-05

1988-08-30

Schreyer, Stafford D.

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Monitoring

379 33, H04M 124

Patent

active

047682175

ABSTRACT:
A public telephone set includes a speech circuit including transmitting and receiving amplifiers for forming a channel loop and two pairs of conductors for respectively connecting a transmitter and a receiver in a handset to the transmitting and receiving amplifiers in the speech circuit. The telephone set further includes an energization circuit having a resistor applied with a power source voltage, a latching relay for switching at least one of the transmitter and the receiver through the conductors to the speech circuit or the energization circuit, and a CPU including an internal timer for monitoring a connecting state of the handset by presence/absence of a current supplied to the energization circuit or a voltage appearing in the energization circuit when the latching relay switches at least one of the transmitter and the receiver to the energization circuit.

REFERENCES:
patent: 4039768 (1977-08-01), O'Maley
patent: 4644109 (1987-02-01), Takeda

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