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Thread: Theory: Rasp Pi temp is interfering with TC probe

  1. #1
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    Theory: Rasp Pi temp is interfering with TC probe

    Hello All,

    I have a previous thread with help on my TC probe here:

    https://tvwbb.com/showthread.php?749...board&p=823281

    It seems to have resurfaced as I was seasoning a new UDS I built. After a couple of hours running HM and microdamper the TC went all over the place jumping between the actual pit temp and anything up to 700 degrees. I tried a different TC probe with the same problem. When the HM is cool the TC seems to work fine.

    So I brought unit in to capture some data. I ran the hm-noise firmware. I have uploaded pictures of the setup as well as the csv of the problem, also the temp of the Pi at the time. Also it should be noted that even when the TC was grounded with jumper it still kicked out a very wrong temp.

    It has been some time since I did the clean up of the board as noted in the previous thread.

    Other things I have tried include testing the extension cord used. Changing from a wall wart to a battery backup pack. Tried two different TC probes. Nothing seems to work. I have tried with the AC filter on and off.

    As to the seasoning when I disabled the pit probe and ran off probe 1 the HM ran fine for nearly 24 before my charcoal road bit the dust so otherwise HM is running great with WiFi and fans and dampers all working as expected.

    I even updated to the latest snapshot build in the middle of my "cook" yesterday and no changes.

    You all have been such a great community thanks in advance!

    Here is link to Dropbox with screenshots and pictures of HM and a csv running the hm-noise firmware.

    https://www.dropbox.com/sh/ja1ysq7t9...vN81poGCa?dl=0


    Best,
    Nate
    Last edited by NateSebold; 07-20-2019 at 10:16 AM.

  2. #2
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    Well looking through this thread:

    https://tvwbb.com/showthread.php?780...n-new-HM-build

    I have a similar problem so I tried the same diagnosis.

    When doing the TC amp testing everything looks good except that N is connected to 2. There are no other bad connections that I could find but N and 2 have continuity on my board.

    I ran the hm-noise for a while with the HM out of the case and it was 10 C lower than inside the case and so the TC doesn't kick up any large amount of noise.

    I did not do the battery test after I ran into the continuity error.



    Cheers
    Nate

  3. #3
    TVWBB Guru Steve_M's Avatar
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    The N pin is not connected to anything internally, so it can touch the 2 pins without issue.

  4. #4
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    Thanks Steve. I'm back to a loss. I guess I can do the AA battery test now. I'll report those results back.

  5. #5
    TVWBB Guru Steve_M's Avatar
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    If you take a piece of bare wire or a small paperclip and bend it so that you can stick it into the TC jack on the board, that will short out the TC amp and cause it to read it's own ambient temp. Does that work?

  6. #6
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    Thanks Steve!

    Yeah so I read about that. Yesterday after I had my heatermeter really warmed up and outside in the heat only my TC probe was way high like 600 and then 400 then accurate at like 180 in my pit then 500 it bounced all around. This started about 30 minutes into the cook. I disabled the TC probe and ran off of probe 1 for the rest of the cook. At the end after I was done cooking I was playing with the HM and I did short out the TC like you describe and it was not the ambient temperature it still bounced around.

    This morning going from a cool hm I just fired it up in the house and haven't been able to reproduce the error. It all seems to be working fine.

    I just put the probes in the toaster oven to run a bit on 250 because nothing was happening letting run at room temperature. Hopefully I can reproduce the error. I have been able to get the raspberry pi up to temp it is hovering right around 60 C just like it was at the end of my cook yesterday. So the case is equally warm but I can't reproduce the error.
    Last edited by NateSebold; 07-21-2019 at 11:11 AM.

  7. #7
    TVWBB Honor Circle Bryan Mayland's Avatar
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    The weird phantom noise is the bane of my existence. I've also seen it happen in person so I know it happens and it is just baffling. The HeaterMeter I use for all my cooks hasn't done it since back when I was developing the board. It does seem to be rare for users but not so rare that it can be written off as the ISS flying over and causing electrical disturbance or something. The AD8495's performance is specified within 0C-50C, with operating range up to 125C so it definitely shouldn't start outputting random signals at 60C. I'm not sure what causes it, but it is a pretty high gain amplifier (x122.4) so it wouldn't take much stray voltage to get out of hand-- even 1mV of noise would become over 44F in error.

    EDIT: Strangely enough, if I put my pit probe in the toaster, it picks up a ton of noise and I need to insulate it from touching the any metal for it to read properly.
    I'm that HeaterMeter guy what ruins everybody's free time.

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