Call signal recognition circuitry for telephone subscriber's appts. - has current sensor between rectifier and diode supplying detector sensing frequency

摘要

The incoming call signal recognition circuit for a telephone line has a rectifier (14) allowing the rectified incoming call signal to be used to charge a storage capacitor (C) via a one-way current switch (24). A call signal detector (26) determines the frequency of the call signal from the rectifier output. A current detector (18) lies between the rectifier (14) and the switch (24) allowing a low-ohmic load (R1) to be coupled to the rectifier output when no current is being supplied to the capacitor (C). Pref. the current detector (18) and the switch (24) are simultaneously provided by a transistor with two collectors. USE/ADVANTAGE - Rapid response allowing switching in of loudspeaker propagating more pleasant sound, even a melody, than usual alarm-like bell.