Bell Telephone Laboratories

Lucent Technologies Inc.

At&t Bell Laboratories

Raymond G Jackson

Paul C Davis

Dale Harvey Nelson

Brian Albert Wittman

Joseph J Nahas

DeWitt G Ong

Daniel Warren Macauley

Ronald Lee Wild

Dennis L Whitson

Kenneth F Sodomsky

Robert Anderson Till

A linkage couples the coin return door of a coin telephone instrument to a cam mounted in the coin return chute. When the coin return door is opened in the normal manner by a customer to retrieve coins from the coin return hopper, the cam closes a contact of a microswitch that completes a circuit. After a normal coin retrieval the door closes and the switch contact returns to open. Such momentary switch closures are considered normal. However, if foreign matter has been stuffed into the coin return hopper by a fraudulent user, the material will be engaged by a comb at the end of the cam, preventing the coin return door from closing normally. When the door is prevented from closing normally and remains open for more than a few moments, the switch remains actuated, keeping the circuit closed for longer than normal thereby signaling the signaling the telephone company that the phone has been tampered with.

Coin telephone protection device

A digital-to-analog signal converter (1000) provides an analog output signal by subtracting bit currents reflecting a digital input signal from a constant current source (1004, 1018-1022) at a current summer (1003), with the difference current being applied to a constant load. The subtracting of the current, rather than switching the current, avoids the modulation of an associated power source since the total current demand remains the same. In that low power operation is possible, the converter is particularly suited for use in an arrangement where only a low level of operating current is available from a power source.

Digital-to-analog converter

In a multifrequency generator providing tone signaling for a telephone, the common switching functions are performed by solid state switching circuitry (1200). Improved signal transfer between the telephone line and transmit and receive transducer of the telephone is provided by arranging the solid-state transmit and receive switches (1201, 1401) in a gain configuration to increase the level of the speech signal. The tone signals are digitally synthesized and use an integrated R-C oscillator (600) as a reference. Button down and button up debouncing of a contact closure signal from a single contact per button keypad is provided.

Electronically-switched multifrequency generator with transducer control

In a subscriber telephone set, an active speech network provides a sidetone signal and for equalization of the transmit and receive signals at the tip and ring line port and also maintains the dc voltage at a substantially constant level at this port. The network is compatible with conventional telephone sets and operation on long loops in parallel with such sets is provided for. Internal circuitry (320) within the network check both loop current and tip-to-ring voltage to ensure that both are of a magnitude sufficient for a tone signaling dial (301) to properly generate tone signals before enabling the dial.

Active speech network circuit for a telephone set

Growing community of inventors

Indianapolis, IN, United States of America

Raymond G Jackson