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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 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.

Schematic


Schematic for air flow detector

Parts:


Part
Total Qty.
Description
Substitutions
R11100 Ohm 1/4W Resistor
R21470 Ohm 1/4W Resistor
R3110k 1/4W Resistor
R41100K 1/4W Resistor
R511K 1/4W Resistor
C1147uF Electrolytic Capacitor
U1178L05 Voltage Regulator
U21LM339 Op Amp
L11#47 Incandescent lamp with glass removed (See "Notes")
D11LED
MISC1Board, 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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