- This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space.
- The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.
- When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in the resistance will produce variation of voltage across the filament.
- These variations will be picked up by the opamp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow.
NOTES:- The filament L1 can be made by removing the glass of a 40W incandescent bulb.
- The circuit can be powered from a 12 V DC power supply.
