This gas sensor circuit was found in July 1976 Radio Electronics magazine. The TGS sensor was a common type at the time. Note the power supply to the circuit.
This simple CMOS metronome circuit can be mounted in a small box, providing both sound and light...
Although indicated in the original publication of the 1980s as a capacitance switch, the circuit...
In the figure below we have a simple way to do chroming, silvering or another type of...