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 circuit, from an old publication from the 1970s, can be made with silicon transistors like...
We find this circuit in documentation from the 1980s. The triac and diac are of conventional types...
The purpose of this circuit is to convert a short-lived pulse into a negative rectangular pulse. The...