H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/57, 324/59
H04M 3/22 (2006.01) G01R 17/02 (2006.01) H04M 19/02 (2006.01)
Patent
CA 1081875
DIGITAL MEASUREMENT OF THE DC VALUE IN AN AC SIGNAL ADAPTED TO TELEPHONE OFF-HOOK DETECTION Abstract of the Disclosure The duty cycle of an AC telephone off-hook signal is measured by means of comparing it with the duty cycle of a known AC signal having a duty cycle of 0.5 because it has a DC component of zero. Measurement of the duty cycle in a telephone off-hook detector application involves measuring the DC portion of the signal on a pair of telephone lines from a telephone handset to an exchange. A high frequency master clock oscillator with a much higher frequency than the basic ringing voltage is used. An input signal is used to gate clock pulses when the input signal is positive to a counter. At the end of a predetermined number of clock pulses, the counter is gated into memory connected to a decoder for transmission of the decoded signal to the exchange for appropriate action.
293003
International Business Machines Corporation
Na
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