Telephonic communications – Polystation line system – Automatic or unattended
Patent
1985-07-10
1987-05-26
Schreyer, Stafford D.
Telephonic communications
Polystation line system
Automatic or unattended
H04M 1536
Patent
active
046691120
ABSTRACT:
An automatic telephone number indicating device for connection within the tip or ring line of a telephone circuit of one party of a multi-party circuit for applying a ground mark in response to an interrogation signal from the telephone central office when the party having the device has taken the phone off hook including a current detection circuit connected within the remote telephone circuit for detecting a current caused by the phone being placed off hook. An enable circuit is triggered by the current detection circuit and is held triggered by a time constant circuit for a predetermined time period. A ground mark circuit connects the ground mark between the ground and the tip line or tip and ring lines. A voltage monitor circuit is rendered conductive in response to a voltage across the tip and ring lines, which disables the ground mark circuit. The central office interrogates the circuit by removing the voltage across the tip and ring lines thereby permitting the ground mark to be applied. The central office will then test for a ground mark between ground and the tip line or tip and ring lines. The presence of the ground mark indicates the party having the device is off hook.
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