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Air Flow Detector

Air Flow Detector

This simple circuit uses an incandescent lamp to detect airflow. With the filament exposed to air, a constant current source is used to slightly heat the filament. As it is heated, the resistance increases. As air flows over the filament it cools down, thus lowering the resistance. A comparator is used to detect this difference and light an LED. With a few changes, the circuit can be connected to a meter or ADC to provide an estimation on the amount of air flow.
Part Total Qty. Description

R1 1 100 Ohm 1/4W Resistor
R2 1 470 Ohm 1/4W Resistor
R3 1 10k 1/4W Resistor
R4 1 100K 1/4W Resistor
R5 1 1K 1/4W Resistor
C1 1 47uF Electrolytic Capacitor
U1 1 78L05 Voltage Regulator
U2 1 LM339 Op Amp
L1 1 #47 Incandescent lamp with glass removed
D1 1 LED
MISC 1 Board, Wire, Sockets for ICs, etc.

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