This circuit was found in 1960s Radio Electronics. The circuit uses components from that time. The triac is according to the controlled load. The sensor is a common LDR.
Motorola suggests this circuit in an 80's documentation. The circuit uses an inverter to produce a...
The circuit below is found in the manuals of several manufacturers in the LM123 series of...
This protective circuit for power lines was found in a Radio Electronics from November 1957. The...