7 segment display thermometer

Discussion in 'The Projects Forum' started by tresguey, Jul 14, 2013.

  1. tresguey

    Thread Starter Member

    Apr 22, 2013
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    I have a few LM34's and 7 segment LED's and am wanting to make a thermometer in a 12 vdc environment. I am very new to electronics and would like some help. If anyone knows of an online tutorial that can help me it would be much appreciated.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Well really what you need is help building a voltmeter and controlling the display of it. The output from the LM34 is simply a voltage and you could use an op-amp (or 2) to produce whatever offset and scale you need for your voltmeter, so that it reads temperature.
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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  4. tresguey

    Thread Starter Member

    Apr 22, 2013
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    Yes, this is what I wanted help with. I saw a max138 chip on another site and thought I can use it. But with potential temperatures of over 200 I think something different should be used.

    I did see the harbor freight temp sensor. I was thinking of using it but I need to see the display in very low light. Plus I want to challenge myself and build it from scratch.
     
  5. WBahn

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    Mar 31, 2012
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    Temperatures over 200.... what? Units matter!
     
  6. tresguey

    Thread Starter Member

    Apr 22, 2013
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    The typical temperature I will be reading will be between 80 - 230 degrees.
     
  7. WBahn

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    Mar 31, 2012
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    Come on!!!

    There is a HUGE difference between 230°C and 230°F.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    No worries at 200°K !
     
  9. WBahn

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    Mar 31, 2012
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    Maybe other worries at 200K -- and even more at 200R.
     
  10. tresguey

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    Apr 22, 2013
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    Not really understanding...the temps I would like toes sure are in fahrenheit...this would be what the LM34 made for correct?
     
  11. tracecom

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    Apr 16, 2010
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    That's correct.

    In essence, what you are planning to do is make a digital voltmeter, which will require a specialized IC like the ICL7107 or a programmed micro-controller. To attempt one with individual components would be a very difficult project.
     
  12. WBahn

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    Mar 31, 2012
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    Well, how were we supposed to know your numbers were in Fahrenheit since you wouldn't tell us that until now. We are not mind readers.
     
  13. tresguey

    Thread Starter Member

    Apr 22, 2013
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    Sorry about that. I guess I just forget there is a metric system out there.
     
  14. blueroomelectronics

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    Jul 22, 2007
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    Is this for a car?
     
  15. tresguey

    Thread Starter Member

    Apr 22, 2013
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    No, this is for a mobile brew station(Ale's).
     
  16. wayneh

    Expert

    Sep 9, 2010
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    Are you sure you don't mean a thermostat instead of just a readout?
     
  17. blueroomelectronics

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    Mobile? Huh?
     
  18. BobTPH

    Active Member

    Jun 5, 2013
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    iBrew?

    Bob
     
  19. WBahn

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    Mar 31, 2012
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    The LM34 is scaled for 10mV/°F. For the range you are looking for you would get 0.8V to 2V. That is a nice range for most microcontrollers and so if you chose one that had an internal ADC and enough outputs to drive your display. Assuming you used three separate 7-seg displays, then you would need 10 I/O pins. As long as the I/O pins can sink the total max current of one of the displays, you would not need a buffer transistor, though putting those in would be easy. The LM34 device performance will probably limit you to about ±1°F, so there is little point worrying about using an ADC that can resolve much better than that. So that would be 10mV/2V => 1 part in 200. So an 8-bit unipolar ADC would be sufficient. If you can scale the reference voltage to 2.55V (or perhaps 2.56V) your ADC output would be directly in degrees Fahrenheit.
     
  20. tresguey

    Thread Starter Member

    Apr 22, 2013
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    Thanks for your help, I teach home brewing techniques. Some of the events I attend do not have easily assessable power. So I have built my brew station to run on a 12 volt system. Eventually I will want to automate my transfer pumps and sparge system. But this will take time as I am slowly learning about electronics. I know I can easily go out and buy this equipment, but I like building things with my own two hands. Plus I get to learn along the way.
     
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