This circuit uses a photo-SCR or LASCR that is not a common component today. The relay depends on the load, and the power is supplied by the power grid.
This circuit was found in a 1971s English magazine. We can still assemble it using BC548...
The circuit shown has the component values calculated for a frequency of 1 kHz. TL064 can also be...
Obtained from a 1996 documentation, this circuit uses common components and has a voltage gain of 200...