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.
Obtained from an English publication, this circuit actually needs a current limiting resistor,...
This circuit has its gain determined by the control DC voltage. The circuit is from a Radio...
This oscillator is a 1950s application of one of the first types of commercial transistors, the...