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 it's 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.
Parts:
R1
100 Ohm 1/4W Resistor
R2
470 Ohm 1/4W Resistor
R3
10k 1/4W ♦Resistor
R4
100K 1/4W Resistor
R5
1K 1/4W Resistor
C1
47uF Electrolytic Capacitor
U1
78L05 Voltage Regulator
U2
LM339 Op Amp
L1
#47 Incandescent lamp with glass removed (See "Notes")
LED
MISC
Board, Wire, Sockets for ICs, etc.
Notes:
1. The glass will have to be removed from L1 without breaking the filament. Wrap the glass in masking tape and it in a vise. Slowly crank down until the glass breaks, then remove the bulb and carefully peel back the tape. If the filament has broken, you will need another lamp.
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Source: Electronics Lab
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