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
| Part | Total Qty. | Description | Substitutions | | 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 (See "Notes") |
| | D1 | 1 | LED |
| | MISC | 1 | Board, Wire, Sockets for ICs, etc. |
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- 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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