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 circuit is from a publication from the 70s. The operational amplifier is from the period. Modern...
We found this circuit in the October 1992 issue of Radio Electronics magazine. The duty cycle can...
This circuit digitally counts input pulses. The circuit from a November 1970 Radio Electronics uses...