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.

Author

142 Comments

  1. anjit mahato

    sir, i want to make air floe detector circuit so please send me the details of it.thanku

  2. shobika.

    Sir,
    I need detailed explanation about this circuit. And I want to know that whether output will be there

  3. soudip sinha roy

    Here in this circuit the o/p voltage range of IC 7850 is exceeding the i/p of LM339. Thats why is’n working properly, we should use a regulator before adding the lm339.

  4. 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

  5. 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.

    • 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.

  6. sir.
    please send the advantages and documentation of this air flow detector project.urgent

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

    • 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.

    • Seetharaman

      It should be a bare filament directly in touch with the atmosphere.

  8. plz send me to all the details of air flow detector

  9. sir, can you please tell me what can be used as a substitute of filament?
    and is that R4 a variable resistor??

    • Seetharaman

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

  10. mallika roy

    sir,
    plz send me report and i need its applications and significance of air flow detector.

  11. plz.send me a documentation of air flow detector usig filament.&also working of each r&c,plz—plz—-

    • instead of led we can use siren?and send me its rating

  12. 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

  13. Saeedsadeeq

    Hi sir i like to give me the history, working, principle operation and construction procedure of an air flow detector

  14. rajeevkumar

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

  15. 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.

  16. 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.

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

    • 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

      • 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.

  18. 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.

  19. Tahsinur Rahman

    Hi,sir i want to know measure the rate of air flow..How i can improve that..pls reply…

  20. 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

  21. what is the function of each resistance and the function of the capacitor?pls help

  22. 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………….

  23. 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………….

  24. 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……….

  25. sir i would like to know the function of the resistor R4.. is it a potentiometer?

  26. hi sir.can u give us the information about working principle

    • Seetharaman

      Hi Please go through my 31st October comment

  27. Hi sir i wanna work on this project as my miniproject so pls give me an idea about its expenses

    • 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..

    • 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

  28. 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….

  29. anyone send airflow detector final documentation.

  30. 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.

  31. haimobati

    plz send me more detail about this project.

  32. SIR ;
    WHAT IS ADVANTAGE & DISADVANTAGE OF AIR FLOW DETECTOR? HOW IT WORK? PLS REPLY FAST

    • 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.

  33. How can I connect the filament in the bread board? Plz explain… It;s often getting damaged..

    • seetharaman

      Hi Rupa use a bulb and solder it through wires to bread board. (use a 12volt mini lamp used in car dash board)

      • 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

      • 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?

  34. 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..

    • 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)

  35. 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!!!

  36. 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….

  37. it is very essential for young talented guys

  38. 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…

  39. here what is the purpose of ic7805 and r4 is a variable resistor ?

    • 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..

  40. what is the purpose of Ic7805 anf is r4 is a variable resistor?

  41. 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

  42. shweta gupta

    sr plz send me more information about air flow detector

  43. 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?

  44. 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

    • what kind of variable resistor should i use?please help:(

    • 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….

  45. 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.

  46. sir I want the applications for air flow detector

  47. k.anil varma

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

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

  49. 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.

    • 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!!!!!

  50. 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!

  51. 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.

  52. 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.

  53. 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.

  54. 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.

  55. 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 .

  56. vigneshwar

    where the air flow detector is used(list the applications)?

  57. 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?

  58. seetharaman

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

  59. Thanks, but one more question, I can just do it without the tungstan wire right??

  60. Seetharaman

    Hi Min please refer to 26th Oct comment.

  61. 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.

  62. i’ll try that sir 🙂 thanks a lot for your prompt and positive replies!

  63. 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.

  64. 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?

  65. 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.

  66. 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…

  67. 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 🙁

  68. Its a nice work am also doing a project work on the air flow detector. pls if you can send its design to me thanks.

  69. samson Awaje

    Sir, please i may also need its application and significance thanks.

  70. Hi, Its a nice work. am also doing a project work on air flow detector. Please if you could help me with its design.

  71. hemant tewatia

    sir,can u tell, what improvement we done in air flow detector
    any addition can we done???

  72. 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….

  73. ankit rathore

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

  74. M.SHIRISHA

    also explain in detail about application in boiler furnace

  75. M.SHIRISHA

    can u list any other industrial applications of the circuit……..we are asked to give industrial applications

  76. 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

  77. 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 ……

  78. 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.

  79. 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

  80. hi sir..
    may you pls help us upgade ths circuit by putting different levels of required air flow

  81. 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.

  82. 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.

  83. 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

  84. 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

  85. 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.

  86. 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

  87. 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

  88. 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 ……

  89. 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.

  90. 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

  91. 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…

  92. 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)

  93. 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

  94. shashidhar h

    what is the need of IC7805 in this circuit?

  95. sir i want to know whether this circuit can also indicate the direction in which air flows?

  96. 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

  97. 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.

  98. i want the simple diagram of this circuit will you give mee plzz??

  99. manish gaur

    hello, give me some more information about this project

  100. 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!!

  101. 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!!

  102. it is good for air flow sensor and i says thanks more on your advice

  103. project for air flow detector &the fuction of each components & how it works with datasheets

  104. 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

  105. Brighton Zibengwa

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