We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an LDR and R1 adjusts the sensitivity. A relay with the appropriate voltage can be used instead of a buzzer.
This micro AM radio will tune strong stations in the frequency range between 530 and 1,600 kHz....
This circuit was obtained in a Electronics World of 1968. The transistors can be equivalent as the BC558...
Based on an integrated circuit of the time, this circuit appeared in the October 1979 issue of...