This amplifier with gain control was obtained in a documentation from Signetics of the 80's. Transistors are of power and operational amplifiers are not common nowadays.
This simple alarm with latching uses a relay as the main element. The circuit is from a Radio...
This circuit has a maximum output current of 5 A, and the 2N3055 must have an excellent heat sink....
This touch switch has a bistable action and powers an LED. The circuit can be changed to control a...