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Arduino wifi temp 3 wire

e14 Contributor

I'm new at using the arduino and I need some help I have been asked to design a arduino with wifi and using a 3 wire temperature probe capable of measuring down to -90 degrees C and a PC program capable of receiving the data and storing it in a file and activating an alarm when the temperature goes under or over set limits. preferable also to have a display on board for the temperature and the ability to calibrate the probe

 

Q1. What would the best arduino to use

Q2. Is there a kit for 3 wire probes I have had a look and all I can find is 1 wire

Q3. Would it be able to have more than one device running at the same time with no conflicts

Q4. Would anyone be able to design the device for me I am willing to negotiate on the price

 

Note the device is to be used in a bio storage freezer but I would like the adaptability to use it in the lab fridges as well

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    I can write the PC side software and have a reasonable grasp of the arduino and wifi board but I really need the help on the temp probe any help

  • 0 in reply to e14 Contributor

    Hi Phillip,

     

    Temp probes supply an analog value which won't interface with the arduino directly (or at least, not very well).

    You need to design some circuit that will convert the analog value into a digital value that the arduino can understand. Google for 'RTD ADC' - the circuits are not ideal for a beginner, they are quite advanced.

    Another way could be to use a multimeter with logging or a PC interface capability maybe this one, I've not checked in detail.

    It looks expensive, but factoring in your time and design, it could be cheaper than a custom design.

    If you want to do it yourself, one way (which will still involve work) it to purchase a reference design board for an ADC, such as this one which is very low cost ($35). However, you may need to desolder and replace some resistor values depending on your temperature range, to give you the resolution you may want. You'll need a temp probe (or desolder the one on the board and extend it with wires) and by studying the datasheets for that reference design, notice that a 4-wire cable is needed for best results.

    Also, you'll need to locate a reference table for your particular probe of choice, which shows a mapping between temperature and resistance (and interpolate in-between), to get a more accurate final value.

    That particular reference board is connected to an on-board PIC microcontroller; if you want to use your Arduino, you could sever the wires going to the PIC (so that it is not used), and solder on the wires to go to the Arduino. The interface is SPI, which is a popular one and there is lots of information on it online, and in the datasheet for the ADC on the reference board.