Building an Breathalyzer with MQ-3 and Arduino

March 7, 2010

During the First Meeting of Electronic Arts in Florianópolis, we built a Breathalyzer using the Alcohol Gas Sensor MQ-3 and a Arduino Board to use in the last day of the meeting, in which we gave a party. You can see a quick video two posts below. Last days I received many emails asking for the code or how to make one, so I decided to build the sensor again, take pictures/videos and make a tutorial showing how you can make one, so here it is.


Parts Needed:

Here are some pictures from the building process:

To make the LEDs work, I have connected them in sequence using the Digital Pins 2 till 11 (ten LEDs total). Remember to use a resistor between 220Ω and 470Ω for each LED, like shown on the picture below:

To connect the sensor, you have to connect one of the H pin to +5V Supply (use an external power supply for that, it may be too much current for the arduino) and the other one to Ground.

Pin B (any of them) you connect to Ground. And the A pin (also any of them) you connect to the 100KΩ potentiometer as shown on the picture below. In the same pin where you are connecting the pin A, you need to connect a wire to the Analog/Digital Converter in Arduino, that is where you are going to read the Alcohol information.

This is a quick and easy DIY project, but if you have any problem building it, please feel free to post questions!

You can DOWNLOAD the .PDE file HERE.

And now, have a great drinking!!!

Remember, if you gonna drive, don’t drink,
but if you do, call me!!

Category: Arduino, Electronics, Engineering, Hardware


122 Comments

  1. carol — March 7, 2010 @ 6:55 am

    hilarious! joão, how can u be so hilarious!!
    great boys, congrat…
    1. does the beer integrate the part list?
    2. did you use fritzing to draw your schematics?

    kisses

  2. DanielAndrade — March 7, 2010 @ 7:03 am

    @carol

    1. not beer, but Velho Barreiro (stronger 35%, soon I will add video)
    2. I used EagleCad. I tried using Fritzing, but I didn’t liked.

    :)

  3. DIY : Construire un ethylomètre avec un kit Arduino. | Semageek — March 7, 2010 @ 8:16 pm

    […] pouvez retrouver l’intégralité du projet sur : danielandrade.net […]

  4. Don’t worry occifer, there is no blood in my alchohol! - Hack a Day — March 7, 2010 @ 9:37 pm

    […] wrote up a quick tutorial on interfacing with the MQ-3, or better known Breathalyzer from SparkFun with Arduino. While we would have used perhaps an […]

  5. ioniser — March 7, 2010 @ 10:31 pm

    Have you done any work on converting the lvls to Alc/Vol
    eg millilitre(alcohol)/Litre(air)

  6. Tyler — March 7, 2010 @ 11:12 pm

    Good job on the excellent writeup.

  7. Alan Parekh — March 8, 2010 @ 9:48 am

    Great project! I have no need for one but I could test it for you. :)

  8. Gianni — March 9, 2010 @ 10:25 am

    On the datasheet of MQ3 I’ve read that this sensor need a pre-heat time >24hours. Is really needed to preheat the sensor all this time?

  9. DanielAndrade — March 9, 2010 @ 1:47 pm

    @Gianni time > 24h is a lot!
    I’m not sure about that, I didn’t used it to make exact measurements so I can’t tell about it. :)

  10. Michael Hodgins — March 10, 2010 @ 6:30 pm

    Cool. I love that the Arduino can be used for projects like this.

  11. Gianni — March 10, 2010 @ 9:22 pm

    @Daniel: Yes I know >24 is a lot… I suppose that this time period is to obtain most precise measurements

  12. Arduino un monde d’inventions | Aux Zamis — March 22, 2010 @ 3:19 pm

    […] un éthylomètre ? plus d’info là http://www.danielandrade.net […]

  13. dan — March 29, 2010 @ 8:51 am

    Did you use a resistor on the sensor?then what is the value of resistor?thnx!

  14. DanielAndrade — March 29, 2010 @ 5:36 pm

    @dan I used a 100KΩ Potentiometer to calibrate :)

  15. dan — April 6, 2010 @ 8:17 am

    what is the use of pulldown resistor at pin-A of the sensor?should i connect the port A to a resistor?thanx!

  16. DanielAndrade — April 7, 2010 @ 10:10 am

    @dan http://en.wikipedia.org/wiki/Pull-up_resistor
    and yes, you need to connect the resistor :)

  17. Arduino Examples « — April 25, 2010 @ 8:29 pm

    […] Creating a Breathalyzer with Arduino […]

  18. Alejandro — May 6, 2010 @ 3:05 am

    good job. you can make the schematic of the entire assembly and post it?

  19. dan — May 13, 2010 @ 6:25 am

    can you pls post the schematic and all the connections to the breadboard?thanx in advance..=)

  20. Jowie Jabillo — June 30, 2010 @ 12:08 pm

    can you explain this line of code:

    int ledLevel = map(sensorReading, 500, 1023, 0, ledCount);

    and how can we measure the electrical current from the analog input converting to digital output ???

  21. ms — July 15, 2010 @ 4:06 am

    could u post the complete code please? :)
    thanks a lot :)

  22. Michael — July 15, 2010 @ 11:54 pm

    This will NOT work if wired the way you describe. Sensor pin B needs to be connected to VCC, not GND. Current needs to flow between A and B (direction does not matter). If you connect B to GND, and A to GND (through a resistor) no current flows. I have the MQ-3 and use it for similar circuits. Look at the datasheet. Just to verify, I did wire a circuit just as you describe, and of course there is no voltage at the analog input of the Arduino. Just connect B to VCC and everything will work.

  23. Nice Electronic Hardware photos | Change The World Tech — October 2, 2010 @ 6:53 pm

    […] Breathalyzer Image by Daniel Spillere Andrade Tutorial on: http://www.danielandrade.net/2010/03/07/building-an-breathalyzer… […]

  24. Érico — October 7, 2010 @ 11:29 pm

    Is it possible to build the breathalyzer using the MQ-3, but not using the arduino?

  25. DanielAndrade — October 11, 2010 @ 3:28 pm

    Sure it is possible! But you will need a way to measure the voltage from the sensor some other way.

  26. Building A Breathalyzer | PyroElectro - News, Projects & Tutorials — October 12, 2010 @ 5:02 pm

    […] The write-up has the software, hardware and a video of the working project in action. PyroFactor: Read Permalink  |   Email This […]

  27. Breathalyzer | Change The World Tech — October 16, 2010 @ 6:48 am

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  28. Guilherme Nabeyama — December 2, 2010 @ 12:43 pm

    Hi, how good is this breathalyzer, for how long it can measure the alcohol in blood, or this is only measure for a short period of time when the alcohol ate in the mouth?

  29. geoff — December 16, 2010 @ 4:27 pm

    Thanks for this. Very informative, and it helped me build this fireplace breathalyzer for my Christmas party:

    http://vimeo.com/17752413

    I used the light to indicate when it was taking the reading, not display the result — but the inspiration came from your version.

  30. hammy — December 18, 2010 @ 11:26 pm

    For people who are asking how to calibrate it or convert values to mg/L blood alchohol levels, see page 2 on this pdf http://nootropicdesign.com/projectlab/downloads/mq-3.pdf

  31. DanielAndrade — December 19, 2010 @ 10:12 am

    @geoff Congrats!!
    @hammy Thanks for the info! :)

  32. Electronics-Lab.com Blog » Blog Archive » Arduino alcohol breath tester — December 19, 2010 @ 12:22 pm

    […] alcohol breath tester – [Link] Tags: alcohol, Arduino, breath, MQ3 Filed in Arduino, Sensor | 1 views No Comments […]

  33. Daniel Sousa — December 21, 2010 @ 8:35 am

    Very good this project! But, how many doses of “Velho Barreiro” were necessary to test? eheheheheh….

    Daniel

  34. Electronics-Lab.com Blog » Blog Archive » Arduino based breath analyzer — February 5, 2011 @ 10:38 am

    […] based breath analyzer – [Link] Tags: alcohol, Arduino, Gas sensor, MQ-3 Filed in Arduino, Sensor | 2 views No Comments […]

  35. jaclyn — February 18, 2011 @ 3:55 pm

    DO you have the circuit of this project?

  36. DanielAndrade — February 18, 2011 @ 11:03 pm

    @jaclyn what do you mean by that? If I have the scheme?

  37. jaclyn — February 20, 2011 @ 6:53 pm

    Why we need to calibrate the sensor? The pin A of MQ-3 connect to port analog/digital pin 0. The potentiometer 100k one leg connect to gnd and another leg connect to analog/digital pin 0?

  38. lol — February 22, 2011 @ 2:08 pm

    How to calibrate the sensor?

  39. sailor — February 23, 2011 @ 9:43 am

    i bought a Figaro TGS822 sensor, anyone use it??! there is any way to calibrate it…??!

  40. omee khatri — February 26, 2011 @ 2:38 pm

    what a superb project…………… if even provided with brief circuit

  41. DanielAndrade — February 27, 2011 @ 11:36 pm

    @omee what do you mean by that? The circuit is there, just read the post ;)

  42. Kevin Patrizio — February 28, 2011 @ 12:15 pm

    I am in a robotics class in highschool and I am trying to do this for a final project I was wondering if i could use any other boards other than the Arduino board?

  43. Kevin Patrizio — March 1, 2011 @ 4:21 pm

    Is it possible to use a Propellor microcontroller?

  44. DanielAndrade — March 3, 2011 @ 9:57 pm

    Sure you can! Just modify the code

  45. piyu — March 4, 2011 @ 12:54 pm

    how many leg does mq-3 have? 6 or 4?

  46. Kevin Patrizio — March 31, 2011 @ 3:37 pm

    I recently built this breathalyzer to a T. The only problem I have with it is that when its turned on all the LEDS are lite. Why is this? Do I have to edit the code at all? PLEASE HELP!

  47. Daniel Andrade — April 2, 2011 @ 12:38 am

    @Kevin you have to calibrate it with the potentiometer :)

  48. Ian — April 5, 2011 @ 10:50 pm

    Great tutorial guys. This helps loads for my final project.

    I just have one question about the wiring in this picture http://img.photobucket.com/albums/v107/tigerbr/MQ-3.gif

    Is there any way to tell which side is A and which is B? Or can it work either way?

  49. DanielAndrade — April 6, 2011 @ 9:58 pm

    @Ian you can check that there is a difference between A side and B side just looking! :)

  50. Peter — April 19, 2011 @ 4:37 pm

    MQ-3 have 6pins, but in circut you will need only 4 .. look into the datasheet http://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf

  51. Freeduino + Workshop Kit + Ethernet Shield = Ethylomètre on web ! | Blog de Yohann Lepage — April 23, 2011 @ 8:58 am

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  52. Alex — May 7, 2011 @ 12:16 am

    What type of arduino board did you use for the proejct could you direct me to the exact model number?

  53. IShan — May 7, 2011 @ 1:19 pm

    Can u give me a link to ur schematic or circuit diagram about ur project cz i m facing a problem regarding my circuit…
    thx in Advance

  54. DanielAndrade — May 8, 2011 @ 10:13 am

    @Ishan you can make your own schematic looking in the datasheet http://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf

    @Alex You can use any arduino board, i used the 2009. http://www.arduino.cc/en/Main/ArduinoBoardDuemilanove

  55. gokul — May 29, 2011 @ 2:18 pm

    How can we take the output from the ardiuino board to some other application other than the ‘serial monitor’ in the arduino s/w?? we are tryin to develop an electronic nose using artificial neural nw, so we hav to get d o/p in analog form… also the sensor is always showing some values even if we remov it frm ‘alchoholic air’…
    do help me
    thanx!!

  56. Levi — July 17, 2011 @ 8:53 pm

    How should the potentiometer be wired? Should it be connected to my A0 analog port??

  57. Quora — July 24, 2011 @ 1:29 pm

    What are some cool things one might make with the Arduino board?…

    The Arduino is a small, cheap, microcontroller platform that’s easy to get started with. Artists and people with ideas, who may not know a lot about electronics can get good results fairly quickly. What you might make depends upon your imagination. :)…

  58. MQ3 | Materials Find — July 26, 2011 @ 10:49 pm

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  59. Arduino 101 | Widgeting — August 16, 2011 @ 9:59 pm

    […] circuit with an alcohol gas sensor and LEDs. (You can find an example of a similar circuit and code here)The circuits themselves were really simple to understand. We actually had exact diagrams (using […]

  60. Guilherme — August 23, 2011 @ 9:39 am

    Tentei reproduzir o projeto usando o mesmo esquema é o Arduino Mega 2650, mas o sensor MQ-3 retorna apenas o valor 0 (zero), mesmo quando há presença de alchool. O que está errado? Como posso identificar o problema?

  61. Austin Mathew Dilip P — September 2, 2011 @ 10:00 am

    Sir you could have shown the complete circuit diagram along with procedure

  62. Austin Mathew Dilip P — September 2, 2011 @ 10:06 am

    Sir you could have given the circuit diagram along with procedure. Next day after posting this comment could you please show the daigram

  63. Austin Mathew Dilip P — September 3, 2011 @ 7:55 am

    Could you show the circuit diagram

  64. Brendan — September 15, 2011 @ 6:08 am

    I ran across your blog, i believe your web site is awsome, keep writing.

  65. Mike Patton — October 20, 2011 @ 3:22 pm

    Are you still active in answering questions for this project? Or are you tired of it? Ha
    I have what appears to be a common question that I still can’t seem to understand.

    I have the whole circuit built. The potentiometer part I still can’t dem to get right. Or I need to know its right so I can rule it out as my current problem.

    I am realatitvly new to all this, but I have built my own projects in the past

    Let’s please keep it in simpliest terms for everyone.

    100k pot has three legs. One SIDE leg goes to ground. The CENTER leg goes to analog input A0. The OTHER SIDE leg goes to MQ-3 pin A.

    Can you please confirm or correct. Thank you very much!

  66. Getting Started with Breathalyzer « Rob Faludi — October 25, 2011 @ 4:29 pm

    […] model uses the MQ3 Alcohol Gas sensor and gets a significant jumpstart from Daniel Andrade’s implementation. Here’s a video of the first test. It plays “Take on Me” when you’re […]

  67. nick — November 21, 2011 @ 2:17 am

    If you still need help with this send me an email I have just completed an electronic nose using the MQ sensor series and an arduino. [email protected]

    Nick

  68. Rob Gleason — February 8, 2012 @ 6:55 pm

    Hey guys this is an awesome project and I am interested in doing the same for a biomed electronics project. Anyway you could e-mail me a parts list and any pointers? Thanks alot!

  69. GAS SENSOR « carbonitp — February 29, 2012 @ 7:12 pm

    […] http://www.danielandrade.net/2010/03/07/building-an-breathalyzer-with-mq-3-and-arduino/ […]

  70. Hendrik Roedel — March 27, 2012 @ 3:53 pm

    do i have to use the mq-3 or can i use everey gas sensor i want?

    great work btw ;)

  71. Dorin — June 4, 2012 @ 10:34 am

    Hi Daniel,

    did you connect all 6 pins from sensor to the Arduino or only 4 of them ? What value did you used for load resistence ?
    The detection concentration scope of your sensor was 0.05 to 10 mg/L of alcohol or 0.04 to 4 mg/L of alcohol ? I ask you this because I have found on Internet 2 differnts datasheets…

    Thanks

  72. Dorin — June 4, 2012 @ 10:36 am

    Or did you connected like in the link below???

    http://wiring.org.co/learning/basics/airqualitymq135.html

  73. DanielAndrade — June 4, 2012 @ 11:06 am

    Yeah, I just used 4 pins! Because the two A are the same.

  74. Chris — July 16, 2012 @ 12:09 pm

    Hi, would you happen to have a schematic of this project? This project looks exciting and I am just getting involved with Arduino so a lot of the terminology I am still getting familiar with.

  75. DanielAndrade — July 16, 2012 @ 12:16 pm

    What do you mean what happened?
    The schematic is fine, it doesnt show it all.

    Anything I can help you

  76. Chris — July 19, 2012 @ 3:49 pm

    Hi Daniel,
    The schematic is great. Just being as though I am new to this… I can’t see how everything is connected via the photos. Like I see multiple wires going into the (-) negative section but I don’t see in the diagrams what is connected in (-). I’m guessing because I don’t know how to read the schematic being as though I’m just starting off.

  77. calvin — July 31, 2012 @ 9:47 am

    hi daniel
    awesome work!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    i am new and cant understand by the photo pls give a video or something showing how to connect pppppllllllllllllllllsssssssssss
    help me plsplsplsplsplspls

  78. calvin — July 31, 2012 @ 9:49 am

    i have only 1 week left for the exhibition
    and can u show me how to take the reading digitally or by computer

  79. Nicholas — August 15, 2012 @ 11:21 am

    Hi, there im currently doing a final year project about MQ-3 Sensor, so by just measuring the resistance drop on the load resistor, we will be able to know the concentration of the alchohol? as in ppm? Im totally confused, can anyone help to explain this? what does the graph in the datasheet refers to? How do i measure the concentration of gas?

  80. MATEO RAMIREZ — August 15, 2012 @ 3:36 pm

    HELLO!! CAN YOU POST FURTHER INFO ON HOW TO CONNECT THE 100 OHM RESISTOR, IM HAVING TRIUBLE READING THE VALUES FROM THE SENSOR

  81. sudip neupane — September 18, 2012 @ 3:36 pm

    would you please explain the working principle ? i think it will be quite helpful for my final year project.

  82. mattgilbert — December 5, 2012 @ 8:04 pm

    Michael is right. Sensor pin B needs to be connected to power for this to work.

  83. sqqqrly — January 4, 2013 @ 12:48 pm

    RE Fritzing: I love it. But to grow to love it, I had to get the latest beta version. It is very much improved. The version that is in most Linux repos is old.

    If you’re using the Windows version, well, there’s your first problem.

  84. brian — March 13, 2013 @ 3:31 am

    i have made it,,but the sensor is tgs2620..and i can’t calibrating the sensor,,can you help me? simulating by proteus..please send your project in my email,,[email protected]

  85. Building an Breathalyzer with MQ-3 and Arduino - Arduino for ProjectsArduino for Projects — March 21, 2013 @ 7:34 am

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  86. João Miguel Correia — March 23, 2013 @ 8:54 pm

    boas, qual é o código usado, apenas para receber e enviar para o ecra (como os valores certos de alcool no ar)

  87. DanielAndrade — March 26, 2013 @ 4:31 pm

    é simplesmente o int sensorReading = analogRead(analogPin);

  88. Julian — April 2, 2013 @ 4:42 am

    Is the pull down resistor the potentiometer?how do you connect the potentiometer?Urgently need to hear from you =)

  89. Julian — April 3, 2013 @ 12:24 pm

    one more thing..how can i calibrate the sensor using a potentiometer? am still new to these kind of stuff

  90. Romeo Coreas — April 12, 2013 @ 8:46 pm

    el sketch tiene un error tiene el numero de led’s al revés tiene que comenzar del 2 al 11

  91. Lucinda Bel — April 19, 2013 @ 2:36 pm

    Hi,
    I am a third year student, and i have my project abt how to prevent drink driving. Basically my professor last minute he asked me to build a breathalyzer and your work is very good. I had some questions if it’s ok?!
    1. Is it ok to use arduino uno board?
    2. the LEDs are connected to 330ohm resistors right?!
    3. The sensor has 4legs so there are connected to the board and the potentiometer right?!
    Thank you
    :) x

  92. Lucinda Bel — May 1, 2013 @ 9:33 am

    hi, I have one more question if it is ok; what is the output of this breathalyzer? i need to connect the output to a car simulation but i couldn’t find it and besides i am having short circuit for no reason.
    Thx

  93. Lucinda Bel — May 1, 2013 @ 10:40 am

    And the connection from the arduino to the LEDs please
    thx

  94. Siddharth — May 6, 2013 @ 7:17 pm

    Hello..I’m building Alcohol Sensor for my university project but I have to use an mbed instead of audrino and show the results on a LCD display. Can you please guide me how the circuit diagram will look? Thanks

  95. rossi — May 14, 2013 @ 8:30 am

    Hey Daniel,
    I was really excited about your project, so i decided to use the idea for part of my thesis by adding lcd and buzzer and stuff. I want to use a potentiometer for calibrating my sensor, but its a bit confusing for me with the mq3 “useless” legs. Could you please send me the schematic by email, because I didn’t find it in the comment section :( ? Thanks in advance!

  96. dansku — May 15, 2013 @ 4:12 pm

    Hi, I don’t know how is the mbed circuit.

  97. dansku — May 15, 2013 @ 4:16 pm

    Like it’s said on the pos, you connect the pin B to ground and the A to the AnalogPic that connects to one leg of the potentiometer.

  98. Alexa Mejia — June 18, 2013 @ 9:14 pm

    hi I am using this idea as a project but am a little confused on the connections. I already calibrated the sensor the 24 hours as requested so I don’t know if I still need the potentiometer in my circuit. Also I was wondering if you could upload a better picture of how you connected your wires since we can’t really see it very well. I also wanted to know if that is all the code or if it’s only part of it. Iwould appreciate your help so much I have hard time with circuits and I need a lot of help. When I make all the connections all the lights blink.

  99. turw — July 1, 2013 @ 8:09 am

    Hi, i’m newer in the arduino use. I’m interested to the alcohol meter. i want to use it to calculate the amount of the air for my experiment. if i have a continuious air + alcohol stream it’s possible to use the same connection. what can i do if i would use a concentartion of alcohol between 0 and 6 %
    thanks

  100. Rusphil Francisco — August 9, 2013 @ 7:48 am

    how can i put the LCD display in this project and what will be the program help me please!

  101. Rusphil Francisco — August 9, 2013 @ 9:48 am

    thanks!

  102. Rusphil Francisco — August 9, 2013 @ 11:58 pm

    can i use mq2 sensor instead?

  103. Daniel Andrade — August 10, 2013 @ 12:01 am

    MQ-2 is a Combustible Gas Sensor, SnO2, so if you want to make a breathalyzer I would say no. But you can make a SnO2 sensor.

  104. Rusphil Francisco — August 10, 2013 @ 12:31 am

    well you don’t use the LM7805 in here? where did you get the supply?

  105. Rusphil Francisco — August 12, 2013 @ 12:01 am

    mq303?

  106. Rusphil Francisco — August 13, 2013 @ 7:51 am

    what if i use mq303 ?how will i connect it? it has 3 pins,

  107. Daniel Andrade — August 13, 2013 @ 10:00 am

    Try looking it’s datasheet!

  108. Rusphil Francisco — August 17, 2013 @ 4:13 am

    why is not working?

  109. Daniel Andrade — August 17, 2013 @ 10:23 am

    Show me the code!

  110. Rusphil Francisco — August 18, 2013 @ 11:14 am

    it just use ur code but using mq303 it has 3 pins, the 2 is i connected to the A0 and the 1 is grnd and 3 is +5v. i just change the sensor by mq303

  111. Alexa Mejia — August 19, 2013 @ 6:48 pm

    hi i had a question what does this part of the code for and what do the numbers stand for
    int ledLevel = map(sensorReading, 500, 1023, 0, ledCount

    also im trying to get the BAC percentage with a seven segment display how would i do it

  112. Nice Hardware Components photos – TECH TALK KING — August 25, 2013 @ 4:49 pm

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  113. Measure Who’s the Drunkest (+ Avoid DUIs) with a DIY Arduino Breathalyer - Science & Tech | Tech wikiHow — October 21, 2013 @ 12:56 am

    […] posted instructions, schematics, and all the code on his blog, so you can head over there if you want to build your own. Watch the video below to see it in […]

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  115. kserkses — November 18, 2013 @ 3:41 pm

    Hi. How to read values from MQ-3? Or this code above is enough?

  116. Daniel Spillere Andrade — November 18, 2013 @ 3:45 pm

    That should be enough! :)

  117. kserkses — December 2, 2013 @ 9:07 pm

    another question ;)
    Red led light is on faster than green, because green LED shines very poorly.
    How to fix it?

  118. kserkses — December 5, 2013 @ 7:01 am

    another question ;)
    Red led light is on faster than green, because green LED shines very poorly.
    How to fix it?

  119. Tristan Novak — February 20, 2014 @ 2:41 pm

    Hello, I am looking at the power consumption of this sensor. The heater will draw about 150mA max. My Arduino has a UA78M05 regulator, which can supply 500mA max. Therefore, if I don’t interface with too many other things, I should be able to power this from my Arduino, right?

  120. Thomas Boyer — April 11, 2014 @ 9:10 am

    Hello, I was just wondering, can we do this on a raspberry ?

  121. Daniel Spillere Andrade — April 11, 2014 @ 9:29 am

    Why not? You will only need an Analog to Digital Converter, something like this: http://www.adafruit.com/products/1085

  122. nithin poovanna — May 6, 2014 @ 3:36 pm

    hi,i wanted to know whats the output of the MQ-3 sensor ,what does the 500-1023 range specify exactly ,what values are those?does it provide the output in millivolts or is it the BAC values ?


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