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My first Arduino (Seeeduino actually) attempt w/ a thermocouple.

Discussion in 'Arduino' started by Dacr0n, Apr 27, 2009.

  1. Dacr0n

    Dacr0n Member

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    Okay... so I've got a Seeeduino board on the way and a couple different thermocouples. My goal for right now is to be able to hook the TC up and read the temps VIA my laptop... Is that possible? Eventually, I want to integrate the signal from the TC into a more complex set of instructions that is part of a PID control script.

    I am in the process of learning the C language to please bear with me. :)

    Another thing on my mind was if I could just hook the TC straight to the board or am I going to need a TC amplifier chip?


    Thanks in advance!

    [​IMG]
     

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  2. Mr RB

    Mr RB Well-Known Member

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    Does that version use a proper PIC chip?? Or are they still using those silly AVR things?
     
  3. Sceadwian

    Sceadwian Banned

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    Silly AVR things? Don't be posting fighting words Mr RB =)
    Seeeeduino is just an Arduino clone. Atmega168 @ 16mhz
     
  4. dave

    Dave New Member

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  5. Dacr0n

    Dacr0n Member

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    I have no idea if its PIC or AVR..

    Whats the difference anyways?


    Any thoughts about my previous questions?
     
  6. Sceadwian

    Sceadwian Banned

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  7. Leftyretro

    Leftyretro New Member

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    While thermocouples are cheap and rugged they are somewhat complex and expensive to interface to micro-controllers. There needs to be amplification, cold junction compensation and finally linearization. Unless you require the high temperature range of a TC you are probably better off looking at other temperature sensors.

    Lefty
     
  8. Sceadwian

    Sceadwian Banned

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    Thermistors are extremely easy to interface to micro controllers.
     
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  9. Dacr0n

    Dacr0n Member

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    Okay well I have a few NTC thermistors. I guess I can start with that...

    How does this look?
    [​IMG]

    The one I have is the 1,000Ω @ 200C.


    Is there any preferred way to hook the thermistor up to the board or do i just hook it straight up to an analog input?
     

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  10. Leftyretro

    Leftyretro New Member

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    It will not function wired straight to a analog input pin. You must have it as part of a voltage divider network such that there will be a DC voltage that changes proportionally with the TC's temperature. It will have to be designed such that the voltage developed is limited to a 0 to 5vdc output for direct wiring to most microcontroller chips A/D input. You then have to deal with linearization if using other then a pretty narrow temperature range, depending of the temperature curve of the specific thermistor.

    Lefty
     
  11. Dacr0n

    Dacr0n Member

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    Okay. Thanks for that info lefty.

    I am not too concerned with linearization because I'm just going to be working with a fairly narrow temp. So temp curves and linear feedback shouldn't pose much of an issue for this project (kind of a continuation of my previous project).

    So what you're refering to is roughly something like this lefty?

    [​IMG]

    In reference to fig (A), Where my thermistor would take place of R1 or R2 in this circuit?

    and the output to the arduino could either be B or C and ideally between 0-5 volts?
     

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  12. Leftyretro

    Leftyretro New Member

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    Well a NTC (negative temp coefficient) would have to be installed in the upper leg of the divider so that the resulting divider voltage would rise with increasing temp. If if was a PTC (positive temp coefficient) device it would have to go in the lower leg. Not sure about your source voltage values and 100vdc is very dangerous around 5 volt logic devices. Perhaps someone here has a validated circuit that is know to work correctly and safely with a micro? What total temp range are you looking to cover?

    Lefty
     
  13. Dacr0n

    Dacr0n Member

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    150-180C

    And I would most likely be working with a 12 volt supply source.
     
  14. Sceadwian

    Sceadwian Banned

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