This circuit uses a heated filament as a sensor. With the air current it changes resistance, and the circuit detects it. The circuit is from a 1969 EEE.
This bidirectional current sensing circuit was found in a 2005 Linear Technology application manual....
This circuit recognizes an input signal at the frequency of 10 KHz with amplitude from 200 mV. The...
This sequential light effect was obtained in a 1992 documentation, but it can be easily assembled...