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.
We found this project in a 1982 publication. What we have here is an audio signal relay trigger, which...
We found this circuit in an old French documentation from the 70s, but it can be assembled using...
We found this circuit in an application note from Linear Technology of the 90s. The circuit uses...