The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 30, 1988
Filed:
Jun. 05, 1987
Tamura Electric Works, Ltd., Tokyo, JP;
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.