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 1 MHz oscillator was found in an Electronics World of 1969. The circuit uses a...
This circuit converts a signal from any waveform into a rectangular or square signal of the same...
Found in American documentation from the 70s, this circuit uses components of the time, uncommon...