schaltungsanordnung to seek acoustic feedback in change and intercoms

摘要

The fault indicator shows a calling telephone subscriber when the connection he wants has not been established due to the called party's being engaged or because of a fault. The calling subscriber's microphone and loudspeaker are tested. - An engaged tone and a call tone are generated for test purposes by operating a selection button (T1') that connects the microphone amplifier's (MV) supply voltage temporarily to the loudspeaker output amplifier (EV) via a capacitor (C). The exchange (Z) applies a supply voltage to one input of an AND-gate. This voltage is passed via a diode (D) to the output amplifier.