The time of this timer depends on C1. The circuit was found in the July 1994 Electronics Now magazine. The supply voltage depends on the relay and can go up to 12 V.
This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The...
We found this circuit in an American publication from the 80's translated into Portuguese. The...
We found this circuit in an old French documentation from the 70s, but it can be assembled using...