Fairchild Camera and Instrument Corp.

Comdial Corporation

Don W Lake

Nagaraja Subramanian

Disclosed is a switch selector and actuator for use with a telephone repertory dialer and the like where a plurality of contacts are arranged in a row. A rail member is mounted in close proximity to the row of switch contacts and is yieldably biased away from the contacts. A selector member is slidably mounted on the rail member and movable to select a switch contact to be engaged. By depressing the selector member and rail member the contact is engaged.

Switch selector and actuator

A digital signal generator that produces multi-frequency tones in the voice band range for use in telephone station sets utilizing multitone dialing. Amplitude information describing each of eight voice band frequencies is digitally encoded into a sequence of multi-bit words describing the amplitude at successive data points along the waveform. The eight frequencies so encoded are separated into four upper and four lower frequencies and stored in two solid state read-only memories. Upon command amplitude data words for one upper and one lower frequency are sequentially read out of the memory in time synchronization, added, and their sum applied to a digital delta modulation circuit. The delta modulator determines the change between two successive data word sums and describes the change by an output of either a binary one or a binary zero. The delta modulator output thus comprises a series of binary ones and/or zeros forming an aperiodic digital pulse train which is applied to an output module consisting of an integrating network to synthesize an approximation of a multitone dialing waveform which is compatible with the common carrier telephone network.

Digital multitone generator for telephone dialing

A solid state signal generator for producing frequency combinations such as used in multi-tone telephone systems. The output of a crystal oscillator is divided to obtain binary signals proportional to the selected pairs of the seven multi-tone frequencies. These signals are scaled with selected binary output signals generated by a free-running pattern generator and representing slopes at various points on a sine wave to produce a binary signal stream that is applied to a controlled charge digital-to-analog conversion circuit that partially charges or discharges a capacitor in accordance with the binary 1's and 0's to produce an output waveform across the capacitor that corresponds to the combined pair of selected individual tone frequency sinusoids.

Digitally synthesized multi-frequency signal generator

A digital signal generator that produces multifrequency tones in the voice band range for use in telephone station sets utilizing multitone dialing. Amplitude information describing each of eight voice band frequencies is digitally encoded into a sequence of multi-bit words describing the amplitude at successive data points along the waveform. The eight frequencies so encoded are separated into four upper and four lower frequencies and stored in two solid state read-only memories. Upon command amplitude data words for one upper and one lower frequency are sequentially read out of the memory in time synchronization, added, and their sum applied to a digital delta modulation circuit. The delta modulator determines the change between two successive data word sums and describes the change by an output of either a binary one or a binary zero. The delta modulator output thus comprises a series of binary ones and/or zeros forming an aperiodic digital pulse train which is applied to an output module consisting of an integrating network to synthesize an approximation of a multitone dialing waveform which is compatible with the common carrier telephone network.

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Cupertino, CA, United States of America

Don W Lake