Air flow detector circuit.

Description.

This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space.

The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in the resistance will produce variation of voltage across the filament.These variations will be picked up by the opamp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow.

Circuit diagram with Parts list.

air-flow-detector_circuit.JPG

Notes.

  • The filament L1 can be made by removing  the glass of a 40W incandescent bulb.
  • The circuit can be powered from a 12 V DC power supply.

Show Comments

142 thoughts on “Air flow detector circuit.

  1. Sree

    sir,
    i wish to do this as my mini project ,so please send me a complete report on this project including its advantages, applications ,scope of this in future

    Reply
  2. akhilesh

    Sir
    I am using thermistor so I needed exact connection in the circuit while I tried breaking the bulb and by using the tungsten filament and soldering it damaged it. So I needed some alternative way to do this.

    Reply
    • seetharaman

      If you want to detect air flow in air duct you require a an anemometer which is a mechanical instrument wear and tear will be there. Use electronic method it will accurate for a long time.

      Reply
  3. fahad

    I connected a 6.2v 500ma bulb instead of filament and it is not working…
    when i connected filament it is not getting heated..

    Reply
    • Seetharaman

      The current source should be capable of supplying 50mA to the filament. around 80 to 100 ohms in value. if your filament resistance is more than 100 ohms this circuit will not work. you have to use portion of the bulb filament instead of full length. use around 50 to 60 ohms of it.

      Reply
    • Seetharaman

      r4 is a potentiometer and the filament can be replaced with low value PTC resistance(positive temperature coefficient resistance)

      Reply
  4. vish

    Dear Seetharaman, i am doing a project very similar to this. It is like im using a wind flow sensor. Is there any way that you could help me with this please? Thanks in advance

    Best regards
    V

    Reply
  5. rajeevkumar

    sir the result is coming oppositely to ur saying.when air flows through the filament the brightness of bulb is decreasing

    Reply
  6. Seetharaman

    Hi Adnan you have to use low ohmic PTC (33 ohms). LM339 can drive a maximum of 6mA, hence you have to add a transistor to take care of the drive current of the relay.

    Reply
  7. ADNAN

    Hi sir. Can i use any thermistor or air sensor instead of L1 filament?
    if yes, kindly suggest which sensor or thermistor can be used.
    Moreover, can i directly operate the relay at the output pin #2 of LM339?
    Looking for your kind reply.

    Reply
  8. duncan

    hi sir, help send me a report on airflow because am interested in doing this project but i have litle knowledge. thank you

    Reply
    • Seetharaman

      Air flow detector is user to find the adequate air flow in a system. (may be a bower or a cooling fan air flow) Here the positive temperatue coefficient charecterestic of the bulb filament is used for detecting the air flow(the air flow will cool the bulb filament (which is heated by constant current flow through it). Once the air flow decreases the bulb temperature will increase its resistance will increase which will detected and indicated by the LED.
      Reply

      Reply
      • Anmol

        sir,
        I am making this project in my college and i am required to submit the report but due to lack of adequate information i am unable to make the report. so kindly help me by providing some more information on this topic or your report on this project. Thankyou.

        Reply
  9. Anmol

    Hi Sir, i am doing a project on air flow detector and i have to submit a report on that but i dont have enough information to make the report. So i request you to give some more information about the project or post your own report.It would be of great help for us.Thankyou.

    Reply
  10. J.Hepzibah beulah

    Hai sir, i want to know the complete info that how much amount of air this circuit detects. and added that what is the replacement for filament in this circuit. how can i enhance this circuit in real time applications. ive chosen this as my mini project in this sem . so please send all these informations to my mail soon. thank u very much

    Reply
  11. nagaraj

    can u give me the detail information about application of air flow detector and where it is mainly used………..? plz give me the answer,im doing mini project on this topic sir……….
    sir,any other circuit is previously used for air flow detection? if its used, can u send circuit diagram and drawback for that circuit sir………….

    Reply
  12. nagaraj

    sir,any other circuit is previously used for air flow detection? if its used, can u send circuit diagram and drawback for that circuit sir………….

    Reply
  13. nagaraj

    can u give me the detail information about application of air flow detector and where it is mainly used………..? plz give me the answer,im doing mini project on this topic sir……….

    Reply
    • Engr Adnan

      Salam,, dear Aadil, its very cheap project..About PKR.500..
      If u want to learn, don’t see expenses..or work in group..

      Reply
    • M.Tayyab latif

      excuse me if you made this project plz send me the full procedure and appratus of air flow detector i also make this plz

      Reply
  14. gaurav

    hello sir,
    i am gaurav, I am studying 3rd yr(Extc).i am doimg my miniproject on dis air flow dedector topic.

    sir i want to know more details about this project.i am very eager to know dis.so please send me more information about (principle,construction,each elements work) to my mail ID..thank u sir….

    Reply
  15. Debasis Singha

    Please give me a detail description and corresponding circuit diagram of about— a man or any object when enter into a room light/lights automatically switch on.

    Reply
    • seetharaman

      Air flow detector is user to find the adequate air flow in a system. (may be a bower or a cooling fan air flow) Here the positive temperatue coefficient charecterestic of the bulb filament is used for detecting the air flow(the air flow will cool the bulb filament (which is heated by constant current flow through it). Once the air flow decreases the bulb temperature will increase its resistance will increase which will detected and indicated by the LED.

      Reply
      • niki

        hi sir as i have got to do miniproject to design an experiment for an apllication involving minimum of 1 digital and analog unit it .i am full too confused please help me

        Reply
      • karan

        But if i use bulb instead of filament on pcb…den hw wud i show dat air is flowing so d resistance is changing..means i nead a open filament to blow air upon.. So how a bulb can be useful?

        Reply
  16. chaitu svsk

    please do explain the working of each component in air flow detector ckt…
    its very urgent…..Please mail me as early as possible..

    Reply
    • Seetharaman

      Hi Please go through my earlier comment
      March 21, 2010 at 9:54 pm
      Hi Ireti The IC 7805 forms a 60mA constant current source feeding the filament. The voltage drop across it is compared by the comparator IC and the ouput is produced. Normally cold bulb filament resistance is low(a positive temperature coefficient material) as it gets heated up the drop across the filament increases due to which the LED goes on. when the filament senses air flow the heat is removed hence the resistance falls down, due to which the LED goes off. If you want the operation other way, air more than a particular flow to indicate by LED going on, interchange comparator ICs inv and non inv port (4 & 5)

      Reply
  17. NIKHIL

    Sir,
    will you plzz tell me from where i can get the filament or any other component can can i use other than filament???
    plz sir reply me as soon as possible!!!

    Reply
  18. Ayesha

    hello sir,
    I am Ayesha.I am studying 3rd yr(ECE).i am doimg my miniproject on dis air flow dedector topic.

    sir i want to know more details about this project.i am very eager to know dis.so please send me more information about (principle,construction,each elements work) to my mail ID..thank u sir….

    Reply
  19. sir m neeraj...sir please send me aplication of this project...plz sir rply soon...

    sir m neeraj…plz send me aplication of this project…rply soon…

    Reply
    • shoair

      lm7805 is voltage regulator ic, means it can give you only 5 volt dc only..
      wel i dn’t think r4 is variable resistor it’s not the symbol of variable resistor..

      Reply
  20. priya

    helo sir,
    i am doing the same circuit in bread board. i learned from your previous comments that the filament has to be completly removed and soldered but for bread board circuit how should i connect the filament? plz do help me with positive replies

    Reply
  21. D Suseendrakumar

    Sir,
    I’m Suseendrakumar doing my engineering course in Madras institute of technology. Can you pls tell the circuitry to connect the output to the air flow meter so as to measure the air flow?

    Reply
  22. esa saveme edwin

    Hi Sir/Madam
    i am a student of Nigeria Naval Engineering College Sapele and i’m doing a project on this topic air flow detector(design and construction of air flow detector)and this information is very useful to me. so, i request you to please send me more information about this topic to my mail id.
    Thank you Sir/Madam

    Reply
    • jansi

      hello sir,
      I am jansi.I am studying 3rd yr(ECE).i m doimg my miniproject on dis air flow dedector topic.sir i want to know more details about this project.i am very eager to know dis.so please send me more information about (principle,construction,each elements work) to my mail ID..thank u sir….

      Reply
  23. Seetharaman

    Hi Can be used to detect the cooling air flow is sufficient, indicating cooling system is functioning. Can also be used for measuring velocity of moving object > or < than the specified value. you may also go through sept 2nd comment.

    Reply
  24. k.anil varma

    please provide the detail information about this experiment and also tel the working and application of this experiment.

    Reply
  25. chinmay

    please provide the detail information about this experiment and also tel the working and application of this experiment

    Reply
  26. ankit panjwani

    sir,
    sir can u please send me the internal layout of the connections of this circuit so that i can make a pcb for this circuit. i also want the list of applications about this circuit, or where this circuit is used.

    Reply
    • Deepak Mulewa

      Sir,
      will you plzz tell me from where i can get the filament or any other component can can i use other than filament???
      plz sir reply me as soon as possible!!!!!

      Reply
  27. Jaack

    aneesh m calicut the air flow circuit can be used in Heating Vent AirCconditioning, detecting movement of cargo, parts, people, animals. Automobile cooling, combustion etc. Whenever you want to detect absence or presence of a gas. Air is just one could be exhaust if cool enough avoid corrosive gases in detector circuit. Do NOT use to detect flammable or explosive gases!

    Reply
  28. phangsh

    Hi.I’m working for my project using this circuit. May I know what are the functions of all those components used for this circuit? Especially for resistors and capacitors. Please reply me as soon as possible. I’ll be very grateful for your help.

    Reply
  29. aneesh m calicut

    sir,
    sir,

    i am studying 4th semester B.tech(ece)in MG university, and i m doing mini project on this air flow detector and this information is very useful to me.So, i request you to please send me more information and where the air flow detector is used(list the applications)? about this topic to my mail id.

    Reply
  30. vimala

    Hi sir,
    i am studying 2rd B.tech(ece), and i m doing mini project on this air flow detector and this information is very useful to me.So, i request you to please send me more information about this topic to my mail id.
    Thank You.

    Reply
  31. rama

    Hi sir/madam,
    i am studying 3rd B.tech(ece), and i m doing mini project on this air flow detector and this information is very useful to me.So, i request you to please send me more information about this topic to my mail id.
    Thank You.

    Reply
  32. avaneesh

    Hi sir, I am student in University of pune, i am studying in B.E.(electronics) ,if you can give more information about the rest of the circuit, the function of each resistance, and the function of the capacitor, and if there any hints or notes, because iam trying to make a project semilar to this one. You can send them to me by an email.
    and any modification pls suggest me Thank you.
    and any project on temperature sensor .

    Reply
  33. Min

    hello sir, its me again. I’m sorry if I asked to much but is it possibly for you to share with me the picture of the circuit?

    Reply
  34. seetharaman

    Hi Min Tungsten has got a good Positive temperature coefficient (alpha) and will not get oxidized easily hence it is preferred.

    Reply
  35. Min

    I am doing this circuit for my project but It doesn’t work. I really want to do this for my project. My only problem is the Filament, I still don’t know how to connect the filament to the board for testing. Please help me.

    Reply
  36. seetharaman

    Hi Shalini you can use it as it is but it will be bulky you carefully remove the filament including its end connecting stiff wire, and solder the filament through the stiff wire to a small pcb (a standard straight line one or a dotted one – veroboard). now your sensor is ready for use. infact you require a tungstan wire which has a good positive temperature coefficient, which is more suited for the project. since you do not get them freely in the market the simple above procedure is given. you can use a small radio bulb(as small as possible so that it can sense the temperature change big bulbs will take a loger time as they have inert gas filled in, 6 volt 300mA bulb) without breaking it.

    Reply
  37. Shalini

    Thanks a lot sir! But how do i connect the filament in the circuit. Pls help cause i’m pretty clueless about how to do it. After breaking the glass, how do I connect it in the circuit? Only the glass needs to be broken? not the other bulb attachments like the base also?

    Reply
  38. seetharaman

    Hi Shalini you can use the 40watt bulb filament by carefully breaking the glass. this can be best done by keeping the bulb in a thick plastic cover and carefully giving a hit with a sharp tool. now carefully take out the filament and use it. the pot is for the flow level set adjustment. LED will come on when air flow sets in. to ckeck the operation first without any air flow adjust the pot such that the LED just goes off. now slowly bolw air on the filament the LED will come on, indicating the circuit is functioning.

    Reply
  39. Shalini

    Sir, also how do I use the filament specified in the given circuit? It’ll work properly no? I’m relying on it for my project. So awaiting a positive reply…

    Reply
  40. Shalini

    Sir, what is the purpose of the var. resistor (100k – R4)? what resistance do we have to set it to while monitoring the air flow? Pls reply asap… doing a project that needs to be submitted in the next 4 days :(

    Reply
  41. priya

    please do explain the working of each component in air flow detector ckt…the connection is simple n works really good….please send the information to my mail….

    Reply
  42. ankit rathore

    actually i want to make air flow detector as my minor project so can u plz provide me PCB arrangement for this;;

    Reply
  43. M.SHIRISHA

    sir can explain in detail about application of air flow detector in boilerfurnace…………
    can u list any other industrial applications of the circuit……..we are asked to give industrial applications

    Reply
  44. M.SHIRISHA

    Thanks a lot for ur response….
    i got output for the circuit ………but filament is very sensitive it is easily getting damaged…….can u suggest any other component in the place of filament ……

    Reply
  45. fozia

    hi sir
    The project seems to be quite interesting and I would surely try this project this semester.Could you please explain me the project in a bit more details.
    If you can give more information about all the componantst, the function of each resistance, and the function of the capacitor, and if there any hints or notes,& how it works with datasheets.

    Reply
  46. selorm agbo

    I am student in knust, iam studying biomedical engineering,if you can give more information about the rest of the circuit, the function of each resistance, and the function of the capacitor, and if there any hints or notes, because iam trying to make a project semilar to this one. You can send them to me by an email.
    Thank you

    Reply
  47. seetharaman

    Any low noise operational amplifier will do to give the required gain and off set. 725, 308, 071, 3140 etc. the output of this ic can be fed to a 3 1/2 digital display normally comes with 0 to 200mV DC FS.

    Reply
  48. sus

    can i please know which ic an i use to get the analog out put from the filament to be converted to a binary digital output or directly to 7 seg display.

    Reply
  49. seetharaman

    Hi SHIRISHA practical application in boiler furnace air flow measurement, will enable total combustion of oil, coal or gas. air flow measurement through any air duct. for temperature and pressure measurement you have to add suitable sensors like RTD pressure transducer etc.
    to add digital indication you can use the analog value availabe at the filament through amplification, can be calibrated to velocity of air flow by comparison

    Reply
  50. shirisha

    Thanks for ur response sir …….
    can u give practical applications of this circuit in industries………..

    i also want to extend this project….like i want to include numerical indication of air flow level….
    can include any other circuit to detect temperature or pressure in this can you send me circut

    Reply
  51. seetharaman

    Hi Shirisha please go through my march12th comment, that will give you the idea on the principle of operation. air flow meters are of different type. measurement with rotating vane speed is anemometer, and hot filament type is the above one. both are fairly accurate if properly calibrated.

    Reply
  52. shirisha

    i also want to extend this project….like i want to include numerical indication of air flow level….
    can include any other circuit to detect temperature or pressure in this can you send me circut

    Reply
  53. shirisha

    sir can i also know about application of this projec in industry ….more over how this instrument is different form other air flow detectors….i also need advantages,disadvantages and precaution to be taken…
    dont mind please answer to my questions

    Reply
  54. shirisha

    hello sir i am shirisha from gnits……i am doing mini project on air flow detector …….i need complete information about working of this circuit and funtioning of each componenent placed ……

    Reply
  55. seetharaman

    Hi Rupak the standard method is to use a rotating blade anemometer. this uses the principle of cooling due to air flow on a heated wire. as the air flow increases the cooling is greater. as it is a matalic wire with positive resistance temperature coefficient the value of resistance of the filament (sensor) is measured to indicate the flow.

    Reply
  56. Rupak

    sir,
    the project seems to be quite interesting and I would surely try this project this year.Could you please explain me the project in a bit more details

    Reply
  57. adeel

    thanx for giving the information of this project…
    Sir…!
    we are doing a project on air-flow detector…and we need to demonstrate and give the presentation to our Externals in the University…
    so pls provide me the complete informations about the project with diagram & the picture of this project Air Flow Detector…!

    Thanx…

    Reply
  58. seetharaman

    Hi Ireti The IC 7805 forms a 60mA constant current source feeding the filament. The voltage drop across it is compared by the comparator IC and the ouput is produced. Normally cold bulb filament resistance is low(a positive temperature coefficient material) as it gets heated up the drop across the filament increases due to which the LED goes on. when the filament senses air flow the heat is removed hence the resistance falls down, due to which the LED goes off. If you want the operation other way, air more than a particular flow to indicate by LED going on, interchange comparator ICs inv and non inv port (4 & 5)

    Reply
  59. ireti

    Hi sir, I am student in oou ago iwoye ogun state Nigeria, i am studying physics with electronics ,if you can give more information about this air flow detector circuit, the function of each resistance, and the function of the capacitor, and if there any hints or notes, because am to make a project on it. You can send them to me by an email.
    Thank you

    Reply
  60. Seetharaman

    Hallo Usama and Manish IC1 is a constant current source of 60mA for the filament. IC2 is a comparator. With the present circuit the LED will become dim with higher air flow. To make it brighter with higher air flow interchange inv and non-inv inputs of IC2. or alternately return the LED to ground instead of plus 12Volt. IC2 can be replaced with TL071. Happy assembling and enjoy

    Reply
  61. John

    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.

    Reply
  62. gurmeet

    pls sir/madam….!!
    we are doin a project on air-flow detector!!
    and we need to give a good presentation to our teachers….!!
    so pls provide me with the informations about the project!!

    Reply
  63. akshatha

    pls sir/madam….!!
    we are doin a project on air-flow detector!!
    and we need to give a good presentation to our teachers….!!
    so pls provide me with the informations about the project!!

    Reply
  64. Mohamed Anany

    Hi sir, I am student in Cape Breton University, iam studying electronics and control systems,if you can give more information about the rest of the circuit, the function of each resistance, and the function of the capacitor, and if there any hints or notes, because iam trying to make a project semilar to this one. You can send them to me by an email.
    Thank you

    Reply
  65. Brighton Zibengwa

    inclusion of track lay-out will b greatly appreciated by students aspecially. those who take electronics as a hobby

    Reply

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