Telephonic communications – Supervisory or control line signaling – Signal receiver
Patent
1991-06-28
1994-04-26
Dwyer, James L.
Telephonic communications
Supervisory or control line signaling
Signal receiver
379372, H04M 100
Patent
active
053074041
ABSTRACT:
A signal detecting device capable of determining whether automatically dialling transmission is to be carried out by detecting an identification signal sent from an exchange system via a telephone line. The frequency variation of the identification signal is constant since the identification signal is a composite wave of a plurality of constant frequency signals. A pulse train having substantially a constant number of pulses can be obtained by comparing the level of the identification signal provided from the telephone line with a predetermined reference voltage by voltage comparators. Frequency counters count for a constant time period the number of pulses included in the pulse train provided from voltage comparators. According to the count result output of frequency counters, a determining circuit makes determination whether an identification signal is received or not.
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Dwyer James L.
Sharp Kabushiki Kaisha
Shehata M.
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