We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the transistor BC558. The relay has an operating voltage according to the power supply.
This circuit was obtained in a 1967 Raytheon manual. The company's component is an optical coupler with...
This circuit was obtained from a 90s Radio Electronics. The components used are from that time. The...
We found this configuration in a documentation for radio amateurs from 1974. The circuit can be...