Found in a 1980s American documentation, this circuit is based on the common CMOS series activating a relay. The circuit is double-timed.
This circuit is from a 1980s Motorola documentation. The circuit can be made with modern...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...