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 old circuit for circuit breaker cars was found in a 1963 publication. The transistors are...
This circuit was obtained in a 1973 national publication, translated from an English publication of the...
Found in an October 1992 Radio Electronics magazine article, this circuit generates a low-power tone in...