Switch control system using binary signals - has signals applied to input line using optical coupling unit whose LED is connected to input line

摘要

The optical coupling unit phototransistor is included in a Darlington circuit which is connected to the switch. There is at least one threshold transistor stage (I, II) which is inserted between the coupling unit (OK) with the phototransistor (PT) and the switch. The threshold of the system is above the level of signals appearing at the input line output in unfavourable external conditions when the line carries no control signals. There is one transistor (T1, T2) in each threshold transistor stage.