This switches circuit,It can be useful many things.which a output of the circuit can be controlled a bell or other sound source circuit or control relay or SCR.(a circuit for RY1,and SCR2 are used with AC voltage source only) The contact switches (S1, S2 and S3) in the parallel circuit,it were used to control a connect switched circuit, which can usefully for a burglar alarm circuit or control alarm signal.
The two transistors work as switches that are highly uncertain,and do not trigger an error,because no other noise.The conduction of the SCR2 was very stable, because the resistance 1K as parallel to the relay.When the trigger and press the switch S2, which is normally closed for the circuit breaker. To relay to stop working. The LED1 to visit the emitter pin of the transistor Q2, it lights up when the Circuit works.
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