Telephone subscriber line testing device indicating crossed wires - uses Graetz diode bridge with photodetector element across DC diagonal

摘要

The device has the line connected across the AC diagonal of a Graetz diode bridge, with a photo element (K) of an optoelectronic relay, representing the rest contact, across its 05 diagonal. Two adjacent arms of the bridge have a light-emitting element (La,Lb) in series with the respective diode (D) as in DE2910897. The photo element (K) across the bridge diagonal uses two series complementary switching transistors (T4,T5) connected in common-emitter configuration. A single photo diode (J3) is connected between the bases of the two transistors (T4,T5).