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PID data to laptop

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  • PID data to laptop

    I've just PID'd my Gaggia Classic.

    I would like to take the input/output of the PID and record it on a laptop, i.e. I want to record the voltage off the thermocouple (which software can convert to temperature), and simultaneously record the voltage on the output pins that go to the SSR.

    The thermocouple voltage is a few mV (max 4 for the sorts of temps we're talking about), and the output pins are about 9 volts and 60mA. The output to the SSR is really just an on/off signal.

    I am looking for a cheap DIY way to acquire this data and plot it in excel. I've done a little reading and seen some people use microphone jacks.

    Has anyone done something similar? I do not want to splash out on a proper data acquisition sysyem which runs to hundreds of dollars.

  • #2
    G'day mate...

    Personally, I'd recommend you try doing this via one of the excellent Arduino/Raspberry Pi I/O optioned kits that abound these days and which don't cost all that much. Huge amounts of help to be found at a number of user sites too...



    • #3

      RaspPis are useful devices and not expensive. Lots of tutorials on the main RaspPi site and sites in Aust to buy from too (Buy a Raspberry Pi in Australia). RaspPi is prob for what you want to do cheaper than an Arduino.



      • #4
        Some PID controllers have a "proportional" 0-10V output which you could log using the BeanBay multimeter or similar, but they tend to be rather expensive, so it's unlikely yours has this functionality. Your best bet is, as Dimal said probably to do this with an Arduino or something along those lines, RasPi is, frankly ridiculous overkill for this application, unless you're planning to develop much more advanced functionality down the track.

        FWIW, my computer controlled corretto uses a MAX31855 thermocouple amplifier breakout board (you can get them for around ~$10, though I spent a bit more on mine because I needed a proper thermocouple socket) interfaced to an Arduino Pro Mini (~$10) for temperature logging (amongst other things, the Arduino also runs the roaster), it's pretty straight forward to get basic temperature logging working with this setup by following the tutorial on the adafruit website.

        I'd recommend using a separate thermocouple for your temperature logging, thermocouple amplifiers likely don't appreciate having their inputs connected to other thermocouple amplifier inputs.


        • #5
          cheers for the replies, I'm doing some reading about using the Mic jack or Line-in to acquire data, requires a bit of circuitry to be constructed on a bread board, but it's only really a one off thing so might be worth it.

          If it all proves too hard that way I might go the Arduino/Pi route. I was only reluctant as it feels like I could have just skipped the PID altogether and manually programmed a heating cycle and feedback loop that minimises the overshoot my PID is giving me.


          • #6
            I've been playing with an arduino lately and have finally worked out how to measure the voltage coming from the PID controller to the SSR, i.e. how often it gets switched on and for how long each time. Will play around with some settings and do some more measurements and put an update on here in a few days.


            • #7
              Another alternative could be RoastLogger, which I recall has OCR capability (optical character recognition) - you can use a webcam to "read" the temperature displayed on the PID controller.



              • #8
                Very interesting project! I just don't see how the acquired data can be useful unless there is additional control to do a temp profile for the shot. If the RTD is in the usual place outside the boiler like most PID setup for Gaggia Classic, temp offset and lag will be major stumbling blocks for repeatable temp shot profile.