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Air Flow Detector

source: http://www.aaroncake.net/

 

 

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

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.

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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