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.
The presented circuit is used in Power supply to increase the voltage output. The voltage output...
The frequency of the LC resonant circuit must be the same as that of the crystal and the JFET...
This amplifier can be used for public-address or other applications. Three transistors of the time...