Dtmf and rotary dial signal receiver

Details Dtmf and rotary dial signal receiver Dtmf and rotary dial signal receiver

H - Electricity

04

M

379/22, 344/84

H04M 1/50 (2006.01) H04Q 1/32 (2006.01) H04Q 1/457 (2006.01)

Patent

CA 1096076

-67- DTMF AND ROTARY DIAL SIGNAL RECEIVER Abstract of the Disclosure A dial signal receiver for receiving and decoding telephone digit signals in either dual-tone, multifrequency (DTMF) or rotary dial pulse form is disclosed. DTMF digits are accepted, if, simultaneously, both the high and low frequency components, derived from a band-split filter, repetitively pass a short term check; and each component passes a long term check once. The short term checks comprise repetitively measuring the period of two consecutive cycles of each component of the input signal. The long term check comprises measuring the period of a number of cycles of each component of the input signal. The number of cycles for each component is dependent on the nominal frequency determined by the short term check of that component. At the end of a cycle related period, a "window" is opened for a time interval related to the expected frequency, as determined by the short term check. If a short term check pulse occurs during the open window period, the related component is accepted as valid. Rotary dial pulses are accepted as valid if they establish a break in loop current lasting at least a predetermined time period (e.g., 27 ms) followed by a restoration of loop current for at least a predetermined time period (e.g., 9 ms). A main controller controls whether or not DTMF or rotary dial pulse circuits, or both, will be conditioned to accept their related signals, based on externally applied control voltages. An output register and decoder stores data bits related to accepted DTMF and/or rotary dial pulses.

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