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Thread: 4.3 New build Probe issues

  1. #1
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    Question 4.3 New build Probe issues

    It may be the lack of sleep...

    This is my 2nd Heatermeter with the thermocoupler option. However, even after setting probe 0 to the thermocoupler option and default mVC at 5, with no probe plugged in, it's reading around 870F, if I short the connection to read the ambient, I'm getting around 200F.

    With no probes plugged in for 1, 2 and 3, 84F, 63F and 138F

    Any Idea where to start? I checked voltage from the resister to probe 1,2,3 and each were 3.29V

    all of my joints look good and I've cleaned the board of flux! This was a pre-assembled themro option. I'm going to sleep on it but any suggestions would be greatly appreciated!

  2. #2
    TVWBB Wizard Steve_M's Avatar
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    Post a couple pics of the board. Maybe there's something obvious you're missing due to the lack of sleep!

  3. #3
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    Are you sure you didnt forget to install the resistors that stand on end? (by the probe jacks)
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

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    Thanks Steve and Ralph! I have those resistors installed.

    Hopefully these will help! https://imgur.com/a/pamuiZ2

    It's probably some minor, overlooked area I missed or something more...

    I've done a few tests as Bryan suggested. I did note at the top of the probe resistors, it's at 3.3V but does seem to drop more than I was expecting at the other end. Measurements below.

    From ATmega Pins:
    FO1 - 2.6V
    FO2 - 2.82V
    FO3 - 2.01V
    PIT - 1.93V

    From Probe Connector: 3.25V

    No Continuity: Probe GND, 3V3, 0, 1, 2, 3. ATmega: PIT, FO1, FO2, FO3, BFB, and BTN

    AVC 3.29V
    ARE 3.29V

    AGN no resistance

    Probe 0
    current temperature 795.0
    Type Thermocoupler
    mV/C 5
    Offset 0

  5. #5
    TVWBB Wizard Steve_M's Avatar
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    The pics don't reveal anything out of place.

    If you pop out the atmega chip, do you get the same voltage readings?

    The 1.93v from the pit probe is really outta whack.

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    Quote Originally Posted by Steve_M View Post
    The pics don't reveal anything out of place.

    If you pop out the atmega chip, do you get the same voltage readings?

    The 1.93v from the pit probe is really outta whack.
    Yeah, same readings, around 2V

  7. #7
    TVWBB Wizard Steve_M's Avatar
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    Really seems like something is adding voltage to the output trace of the thermocouple. With the unit powered off, if you meter between probe 0 and the rest of the J2 pads is there any resistance?

  8. #8
    TVWBB Honor Circle Bryan Mayland's Avatar
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    J2 will show 20kohm resistance between any two of the food probes and a different value between the thermocouple and any food probe. There's definitely something wonky because all the probes read random values, not just the thermocouple. I said it over email but, the circuit from the thermistor probes to the atmega is super simple 3.3V -> 10k resistor -> probe jack -> 100k resistor / 0.1uF capacitor -> atmega pin so it shouldn't be terribly hard to trace out. If you're not aware of it, there are board images and schematics and voltage reference diagrams available
    https://heatermeter.com/devel/pcb/hm-4.3/

    Somehow they're all feeding each other it seems so it would have to be something big I think. As an extreme measure you could desolder all 3 of the pullup 10k resistors which would make all the food probes float but then there would be less of a chance of them feeding into the thermocouple output and see if that gives you normal readings on that. If it does then you can add them back one at a time to see if adding one starts the issue, then you'd have a more specific set of places to look.
    I'm that HeaterMeter guy what ruins everybody's free time.

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