Help with resistance-sensing relay I'm trying to build

Discussion in 'The Projects Forum' started by rommy, Nov 13, 2012.

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  1. rommy

    Thread Starter New Member

    Nov 13, 2012
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    Hey guys! I have a project I'm working on however I'm not too well-versed in this department so I was hoping someone could shed some light upon what I'm trying to build.

    Well, I'm trying to operate a 12v fan. The temperature sensor has range of roughly 400-200 ohms that I'm working with. (the sensor actually sends anywhere from 2,600 Ohms to 100 Ohms, but the temperature I need to work within sends approximately 400-200 ohms readings I believe) The lower the resistance, the hotter the temperature. I don't know the exact ranges I need to work with just yet as I haven't measured with my multimeter yet, but let's assume the following:


    I need to send a 12v signal to turn on a fan, I can send this to a SPST relay for safety's sake. I need to turn on the fan at a certain resistance (e.g. 200 ohms) and turn it off at a higher resistance (e.g. 300 ohms). I can tap into the temperature sensor's readings to see the exact resistance readings, but my question is, how can I go about setting this up? I'm sure it's more simple than I think but I can't figure it out because I'm not too knowledgeable when it comes to electronics. Any ideas?

    I know someone built something that does this however it's not made anymore, and it was programmable (e.g. install in line of the temperature sensor, set it when the desirable temperature is reached to turn fan on, then set it again when it goes down to the desirable temperature to turn the fan off) but I'm not trying to go this far, I just want the fan to turn on/off at a slightly lower temperature.

    Any help would be greatly appreciated, thank you so much.

    My apologies for any improper terminology used, I'm not too educated in this field but I'm a quick learner.
     
    Last edited: Nov 13, 2012
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Hello Rommy, and welcome to the Forums.

    Unfortunately, your topic runs afoul of our Terms of Service paragraph 6, which reads:

    So, we can't allow further discussion of your desired modification.
     
  3. rommy

    Thread Starter New Member

    Nov 13, 2012
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    I'm sorry, where does my post say anything about automotive modifications? :) I'm simply trying to turn a fan on at a specific temperature.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Can be done with a simple comparator circuit.

    What happened to YOUR post AFTER SgtWookie posted? ;)
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Since you seem to have developed amnesia, here the first couple of paragraphs of your original post, with some highlighting:

    I don't mean to be giving you a hard time; the Terms of Service reflect the desires of Owners of this Board, who allow the rest of us to post here free of charge - as long as we follow their rules.

    The overriding concern is safety. We're not automotive engineers; neither are practically everyone else on the forum. It's a specialized field.

    The only thing I can suggest to you here is that you have your vehicle serviced by a technician who has been factory trained on it in order to maintain it as it was delivered by the factory.

    If you are bound and determined to proceed despite the torpedoes, on the Electronics Resources forum, there is a "sticky" post that provides links to other sites which may support such discussions: http://forum.allaboutcircuits.com/showthread.php?t=54400
     
  6. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Even if SgtWookie hadn't quoted you, moderators can still see any modifications you have done to your post.

    This thread will be closed.
     
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