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Carbon Monoxide detector circuit

Discussion in 'General Electronics Discussion' started by Chris815, Jun 30, 2015.

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  1. Chris815

    Chris815

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    Jun 30, 2015
    New member here, first post. I'd like some advice on how to build a circuit for detecting carbon monoxide gas. I'm building this project fairly low tech and cheaply as it's mostly for fun with some real life useage for demonstrations.

    I've found a sensor online which has a good range of gas detection sensitivity, good enough for me anyway.

    Here's a link
    http://www.amazon.co.uk/Sensitive-Control-Carbon-Monoxide-Detector/dp/B00HG7HZQW

    It has four pins, but I don't know which are the triggers. All of them? How do I connect it up to a simple circuit that, for example, would sound a buzzer as soon as a certain level is detected (can be set on the module) and go off when the under that level.
     
  2. Arouse1973

    Arouse1973 Adam

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    Hi Chris, does it have any markings for the pins on the other side of the PCB. Your going to have a TTL (Digital) output an analog output and +V and 0 V (Common)
    Adam
    Oh welcome to EP
     
  3. Chris815

    Chris815

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    Jun 30, 2015
    Thanks Adam, the product listing states there being a signal output indicator and a dual signals output (analog output and TTL output). TTL output signal is low level, allows to connect with SCM directly. Analog output 0~5V.

    No idea what an SCM is, I've googled around and found nothing other than electronic companies with those letters in their name haha. No idea what TTL is either!
     
  4. Arouse1973

    Arouse1973 Adam

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    Could SCM be sensitive control module? TTL is digital level which for an output is around 0 to 0.4 Volts for a low level and 2.6 to Vcc (5 Volts) for a high level.
    Adam
     
  5. Chris815

    Chris815

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    Jun 30, 2015
    Googled sensitive control module but coming up with nothing. Guessing it's not as simple as connecting some pins up to a buzzer circuit that sounds when the input is triggered by whichever one or two of the pins when it detects the gas?
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Look at the words in the link you provided, I think it's what they call the CO module?
     
  7. Arouse1973

    Arouse1973 Adam

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    I think it could be that simple. What buzzer are you going to use?
    Adam
     
  8. davenn

    davenn Moderator

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    its a pity there are no datasheets for the module
     
  9. Arouse1973

    Arouse1973 Adam

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    Yeah it's poor really. You can get one of the sensor on it's own but for the module I couldn't find one.
    Adam
     
  10. Chris815

    Chris815

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    Jun 30, 2015
    Any 5v buzzer will do, I'll have a look for one later. Yeah I found the sensor data sheet too, the LM393 doesn't want to be found.

    I've found this though, looks like four pins on the first diagram, but being pretty basic with electronics I may be well off?

    http://www.onsemi.com/pub_link/Collateral/LM393-D.PDF
     
  11. Arouse1973

    Arouse1973 Adam

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    That's the IC they are using to generate the TTL level. What I was trying to find was the data sheet for the actual module. However it does tell you the output can sink 20 mA. So you need to find a buzzer that draw this much current or less. Otherwise you are going to need some kind of current buffer on the output.
    Adam
     
  12. Chris815

    Chris815

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    Jun 30, 2015
    Alright. So it should work by hooking up the ground and signal pins in series with a 5v source and a suitable buzzer, the sensor and module together acting as a switch? Or is there a little more to it than that? Electronics aren't usually that simple in my limited experience haha
     
  13. Arouse1973

    Arouse1973 Adam

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    Nope that's it, the LM393 has an open collector output so you connect the buzzer - Pin to the sensor and the + Pin to 5 Volts. These sensors normally draw quite a bit off current in the 150-200 mA region, because they have a heating element inside. So make sure your power supply can supply this much current without overheating.
    Adam
     
  14. Arouse1973

    Arouse1973 Adam

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    Oh one other thing make sure you get a D.C buzzer and not a transducer. People call them the same, but the transducer types require a varying signal to drive them and won't work with just a constant D.C level.
     
  15. Chris815

    Chris815

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    Jun 30, 2015
    Great thanks! Yeah didn't mean ground, meant the power pin. Once I've got it I can play around until it works. So I need a 5 volt DC 20mA or less buzzer.

    As for power supply, maximum voltage is 5, but it'll still work with less, and I need a higher current/high capacity for because of the load from the heater coil. So would two D cell batteries work? That'll give me 3 volts and enough current since they're designed for high drain applications?
     
  16. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    See what the operating range is for the buzzer, it might work with 3 volts and just be quieter. Give it a try.
    Adam
     
  17. hevans1944

    hevans1944 Hop - AC8NS

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    Last edited: Jul 1, 2015
  18. dick56

    dick56

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  19. dick56

    dick56

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    Apr 15, 2011
    Arouse1973 and hevans1944 like this.
  20. Alec_t

    Alec_t

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    Not for long with continuous use. According to the datasheet the sensor average power consumption is ~350mW at 5V, so would be ~ 126mW at 3V. If D cell capacity is 20Wh, 2 D cells should run the sensor for ~ 2 x 20 / 0.126 = 317 hours (< 14 days).
     
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