Air Flow Detector


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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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Comments

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kashyap
Air Flow Detector
Saturday, October 26, 2013 9:22:42 AM
lm 339 is connected to R1 through potentiometer? ??? plzzzzz reply
vanissa
Air Flow Detector
Friday, February 17, 2012 9:13:30 AM
sir ,i want to know witch sensor used in a spirometre who detecte the unspiratory and the expiratory air and please give the the circuit
Samweld
Air Flow Detector
Thursday, September 09, 2010 12:42:23 PM
Quite simple to implement but I'll try it out before I can comment. But then, I'll like to say.. nice job sir.
haris
working
Thursday, May 13, 2010 6:17:44 AM
Hiz is this R4 resistor a variable resistor also instead of the bulb can i use a variable resistor, if yes what should be its resistance?? also my circuit is not working properly when i ground the pin 12 of the U2
anonymous
Air Flow Detector
Saturday, March 27, 2010 11:41:59 AM
Was wondering if anybody could help me out, by assisting me with adding the ADC and a 7-segment counter to the circuit.
Fergus
Air Flow Detector
Sunday, December 27, 2009 3:03:40 AM
To John - have you tried adjusting the value of R5?
anonymous
Air Flow Detector
Thursday, December 03, 2009 12:55:51 PM
I have never seen a schematic with a symbol like that of the arrow coming out of the 5th pin of the LM339, it points directly into the the center of Resistor 4. Does anyone know what this translates to? Thanks.

(Editor's notes: It's a pot.)

John
Air Flow Detector
Wednesday, November 18, 2009 3:34:46 AM
This is a simple but useful circuit, thanks for making it freely available. That said I expected the circuit to function in reverse, instead of the LED dimming when airflow is detected I assumed it would brighten. Any suggestions on how to modify the circuit so that the LED brightens with air movement? I tried reversing the input signal to the comparator and it does work but the output barely lights the LED.
anonymous
Air Flow Detector
Thursday, October 01, 2009 8:33:09 PM
Can i use this circuit to measure speed??
ajinkya
Air Flow Detector
Wednesday, September 16, 2009 9:46:07 AM
how can be the meter joined and which meter and does it need to be calibarated
ajm
Air Flow Detector
Friday, April 24, 2009 11:25:52 PM
R1 and R2 are parallel conected?
alrex
Air Flow Detector
Friday, November 21, 2008 1:23:31 AM
sir, i would like toknow if this circuit can be used to detect the flow of hydrogen gas through a process of electrolysis. i am plannig to used this circuit in my project: Hydrogen torch
RAKESH
Air Flow Detector
Sunday, November 16, 2008 1:15:06 AM
instead of that incandacent bulb which can be used please reply... the circuit is nice in use....
anonymous
Air Flow Detector
Tuesday, October 07, 2008 11:46:27 PM
This is an idea of the Hot-wire Anemometer.You've to heat L1,when air flow pass L1,it's cool down and it's resistance is changed along it's temperature. R4 is used to adjust the reference voltage,you've to adjust it to the highest velocity or at the position that make the LED just blind or use lower resistance,I think value not over 1k may be used.
anonymous
Air Flow Detector
Wednesday, August 27, 2008 10:39:00 PM
How about substituting a tiny positive temperature coefficient (PTC) thermistor in place of L1? That would be a lot safer than breaking light bulbs, and would achive the same result. Many electronic components dealers offer them very cheap too.
anonymous
Air Flow Detector
Thursday, April 10, 2008 5:30:16 AM
i think it will not work properly
anonymous
Air Flow Detector
Wednesday, March 12, 2008 7:44:29 PM
Can some one tell me about R4?... is it a varible resistor or a fixed resistor??.... I have built this circuit many of times but have not been able to get it to work..... Can anyone give me some feedback...thanks!!
vimal raj d
Air Flow Detector
Saturday, March 01, 2008 12:15:10 PM
sir i am going to take this as my project of present semster can i have some more details about this???? plz plz plz
khairul
Air Flow Detector
Wednesday, February 20, 2008 6:29:22 PM
hi there. nice circuit. i have some problems regarding the Incandescent lamp. i would like to implement this circuit into the pspice program but i do have problem to place the incandescent lamp. may i know, if there is a part can replace the criteria of the incandescent lamp in pspice? thank you
Rohan
Air Flow Detector
Friday, February 15, 2008 10:57:47 AM
Sir i want to take this circiut as my annual project,so plz plz send me more details about this cct.
jair frassao
Air Flow Detector
Thursday, January 31, 2008 9:27:00 AM
Hello friends, I can make an alarm for the fan of the motor of a car. When for of ventilating the detector it had informed me.
Michael
Air Flow Detector
Friday, January 25, 2008 6:34:04 AM
I haven't built one yet but I will try next week and let you know how good it is. I will have to trace the bulb first and may take me some time.
anonymous
Air Flow Detector
Tuesday, January 01, 2008 10:38:22 PM
A practical use of this? This is how a Mass Airflow Sensor works in late model cars. The computer must know how much air is flowing into the intake manifold so the computer can keep the air/fuel mixture at 14.7:1 (at sea level). By keeping a voltage constant through a wire in the MAS, the current can be measured to determine the airflow.
Amit
Air Flow Detector
Thursday, November 15, 2007 1:25:45 AM
I would like to know the working of air flow detector and component description.
abdul basit
Air Flow Detector
Tuesday, November 06, 2007 3:25:50 PM
Hai . I am Baist . I am making aproject plz give me some other simple progect ,
mazhar06
Air Flow Detector
Saturday, November 03, 2007 2:34:04 AM
sir i am going to take this as my project of present semster can i have some more details about this???? plz plz plz
Mike
Air Flow Detector
Thursday, October 25, 2007 7:28:00 AM
How would one modify to use a meter for the output??
anonymous
Air Flow Detector
Monday, October 22, 2007 8:00:24 AM
How would one change it to add a meter instead of an led..?
joji
Air Flow Detector
Monday, October 22, 2007 5:14:43 AM
The circuit is interesting .... i want to know the practical application , any substitute for # 47 lamp and the range of flow we can measure...
anonymous
Air Flow Detector
Saturday, October 20, 2007 9:21:09 PM
number 47 lamp is 6.3 volts .15 amp so do the math to find the wattage. number 47 is a fairly common lamp there should be plenty of sources around your town or at least on the internet to find this bulb.
anonymous
Air Flow Detector
Friday, October 19, 2007 7:26:10 AM
this is very interesting.....but i want to know more about practical applications of this circuit ..
sankari
applications
Thursday, October 04, 2007 8:38:25 AM
this is very interesting.....but if you give us the practical applications of this circuit it would be more interesting.......
shin
Air Flow Detector
Wednesday, August 08, 2007 12:02:55 AM
sir,there is problem of 47 incandacent lamp.i cannot find this,is there any substitution?
any
Air Flow Detector
Monday, August 06, 2007 2:33:37 AM
Sir would u plz tell me about the # 47 lamp. what are its characteristics its resistance, its wattage & its current etc. i would b thankful 2 u
anonymous
Air Flow Detector
Monday, July 30, 2007 10:56:51 AM
I think it is too basically for s4 student ,who is looking for advanced project to build
Three Of Five
Air Flow Detector
Tuesday, July 24, 2007 1:05:31 PM
An exposed filament doesn't seem to be a very reliable sensor
faheem anjum
Air Flow Detector
Saturday, July 07, 2007 4:22:46 PM
sir,there is problem of 47 incandesent lamp.i cannot find this,is there any alternate,or tell me its wattage.
niranjan ghimire
Air Flow Detector
Thursday, June 28, 2007 6:50:09 AM
sir/madam, can this circuit model of the air flow detector be used in the application where we can use it in detecting the oxygen flow through the oxygen cylinder...? i also don't know why and how the glass of the incandescent lamp should be removed?
Romel
Air Flow Detector
Tuesday, June 05, 2007 11:47:09 PM
1 thing more in schematic diagram that i seen, is the R4 a fixed or a varaiable resitor.. pls i cant fallow the diagram shown...
Romel
Air Flow Detector
Tuesday, June 05, 2007 11:43:07 PM
can i use an ordenary flourescent bulb instead of #47.. bec. i don't know what is #47 Incandescent lamp and its wattage..
Ravi
Air Flow Detector
Tuesday, May 29, 2007 10:25:07 AM
Its support me lot, thank u
hammad
Air Flow Detector
Saturday, May 19, 2007 1:37:35 AM
Sir would u plz tell me about the # 47 lamp. what are its characteristics its resistance, its wattage & its current etc. i would b thankful 2 u
pebe
Air Flow Detector
Thursday, May 03, 2007 4:44:11 PM
It would help if the voltage and wattage of the lamp were listed. It is not possible to get a #47 in the UK (and I suspect in other places also).
Ram
Air Flow Detector
Wednesday, April 25, 2007 11:37:49 PM
Good Circuit
dennis
Air Flow Detector
Monday, April 23, 2007 9:31:23 AM
sir,there is something that i don"t understand in this air detector,is this 47 incandescent lamp.please show me how it look like.so that i can understand what the air detector well,thank sir.
muoso
Air Flow Detector
Tuesday, April 03, 2007 4:51:54 AM
it's working!
vinay
Air Flow Detector
Wednesday, March 28, 2007 4:10:38 AM
very nice to use in everyday life
fenal shah
Air Flow Detector
Thursday, March 22, 2007 11:47:47 AM
hi will u pls tell me how to break L1?? thank you
DK
Air Flow Detector
Tuesday, March 20, 2007 8:29:45 AM
can you discuss about air flow detector? i need it badly! thx!
anonymous
Air Flow Detector
Monday, March 19, 2007 10:41:49 AM
how to eksplain that....thx it will be helping me
anonymous
Air Flow Detector
Wednesday, March 14, 2007 2:05:58 AM
how to explain it
tejas
Air Flow Detector
Wednesday, March 14, 2007 2:05:32 AM
is there any substitution for #47 Incandescent lamp ?
balan
Air Flow Detector
Tuesday, March 06, 2007 6:33:38 AM
i like this site because we can now more circuit
anonymous
Air Flow Detector
Tuesday, March 06, 2007 2:15:58 AM
please give the layout
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