The voltages shown were in the original design. From the original designer of the circuit: the relay's coil voltage rating is 1/2 the supply voltage. Each of the two resistors are equal to the coil's resistance. I've used 5VDC relays with a 12VDC supply and it worked fine. The value of the cap was just selected by experiment.
Mostly, I just think it's an clever circuit.
Ken
Mostly, I just think it's an clever circuit.
Ken
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