Description.
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.
Circuit diagram with Parts list.
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.
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