Using an LDR, this Philips circuit directly activates a relay when light strikes the sensor. The relay is 45 V with 20k coil resistance. The 220 nF capacitor must be polyester for 400 V.
This circuit was suggested by Analog Devices in a 1990s documentation. The components are from the...
Found in a 1964 Electronic Design, this circuit suppresses arcs that occur in contacts when a...
Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be...