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 uses a CA3140, an operational amplifier with FETs in the input stages. Equivalent can be...
Found in a Popular Electronics from the 90s, this circuit has a configuration that has been widely...
This circuit was found in an American 80s circuit manual. The components used are unusual. The...