Found in the July 1994 Electronics Now magazine, this circuit drives a relay up to 12 V depending on the power supply. The transistor can be general purpose.
This circuit was taken from Maxim documentation from the 1990s. It can be implemented on the basis...
This circuit had its assembly described in Radio Electronics from July 1964. The circuit uses LDRs...
This circuit is from a 1992 publication. The transistors can be the BC549 or BC548 and the power...