Paystation transmitter ground detect circuitry
AssigneePalco Telecom Inc.
InventorGary Grantland
Life of this patent
Estimating the term…
Abstract
A ground detect circuit for use in telephone paystation consisting of a comparator circuit which compares the voltage across a telephone transmitter included in the paystation to prevent users from fraudulent use of the instrument by grounding the handset transmitter to signal the central office that initial rate deposit has been made when in fact it has not. The ground detect circuit upon detecting the presence of ground at the transmitter generates a signal which can be utilized to disable an associated calling device.
Claims5
A telephone paystation connected to a telephone central office via a telephone line, said paystation including a transmitter including first and second input terminals, a calling device, a microprocessor, a transmission network, an earth ground and a ground detect circuit, said ground detect circuit comprising:
- a comparator circuit including first and second input terminals connected to said first and second transmitter input terminals, respectively, said comparator circuit further including an output terminal connected via said microprocessor to said calling device;
- said comparator circuit operated in response to connection of said earth ground to one of said transmitter terminals to generate an output signal at said comparator output terminal whereby said microprocessor is operated to disable said calling device connected thereto.
Dependencies are inferred from the claim text.