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Thread: New HM 4.3 Build - Wonky Pit Probe Port Issue

  1. #21
    TVWBB Diamond Member
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    recent posts are more informative... First, when you say "Probe 1" do you mean the pit probe or food probe 1? (technically the pit probe is "probe 0")

    you mention at first using it as a thermometer and probe 1 working... if you unplug the CAT5 cable from the HM does that probe function properly, or is it still wonky?
    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.

  2. #22
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    did you swap the 100k and 10k resistors for probe 1 on the circuit board?

  3. #23
    New Member Larry Naylor's Avatar
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    First smoke i used the HM only with no cat5 cable attached. Just the thermocouple for the pit temp and food 1 for the meat thermocouple and food 1 worked great. After finally getting a servo i assembled the rd3 and cabling. went to do a second smoke last week and noticed the food probe 1 was measuring a temp of 185 while in my hand moved probe to food 2 & 3 and got normal room temp. Tried 2 other probes in food 1 and they both read 185 in food 1 but normal in food 2&3. Did a 10 hour smoke using the thermocouple and a probe in food 2. After a slight fan adjustment this thing heald solid 225 for the 10 hours. THe voltage readings above are with no cat5 cable attached. Probes are thermo pro and no matter which one is in food 1 it reads 185.I know the readings are slightly low and this could be the meter or true readings . Is there a low voltage threshold for the chip? I'm used to electronics where they lit up and got hot and shattered if dropped. could i have a corrupted programming problem?

  4. #24
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    Alright, more good info. You have TC pit probe, which is working, and you are having trouble with the first food probe. I wanted to make sure we were not talking about the pit probe here.
    The pit probe aside, the probe circuits are extremely simple. There are literally only 3 components between the probe jack and the ATMega, the 10k and 100k resistors that are standing up and the one small yellow (.1uf) capacitor. Check values and soldering on those components, also make sure there isn't excess flux from soldering on those components, if in doubt clean board with isopropyl alcohol and a soft brush (and let dry thoroughly before powering on) Also check the 2nd pin from the corner on the ATMega (should be marked Probe 1 on the board)
    It is unlikely that there is an issue with the ATMega, but I have seen crazier things. You could re-flash the software to eliminate that possibility.
    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.

  5. #25
    New Member Larry Naylor's Avatar
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    I'll scrub with alcohol again. Measured the voltage on the leads on the ATMega all 3 of them that are for the probs i think they are 17,26,25 all of them had the same voltage. Thanks for the schematic.

  6. #26
    New Member Larry Naylor's Avatar
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    oops ment leads 27,26,25

  7. #27
    New Member Larry Naylor's Avatar
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    Scrubbed with the alcohol no change still reads 185 food probe 1

  8. #28
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    Did you reflash the AVR?
    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.

  9. #29
    New Member Larry Naylor's Avatar
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    Don't know what that means { have to confess i have gray hair,and not the most computer savvy). Does that mean pull the sd card reformat to clear it then download the heater meter software then reinstall? That's a lot of thens in one sentence. Before i forget again i want to thank you for the work on your RD3 it was fun putting it together and making the adapter for the grill, your help here is most appreciated. The same applies to Bryan also HeaterMeter is a great device and good kit to build, thanks for your help also.

  10. #30
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Ok thanks for all the clarification, I think I've got a good mental picture of what you're seeing now. That's some crazy behavior for sure. I just checked the voltage on one of my HeaterMeters with a thermoworks pro-series probe at room temperature (76F) and it reads 2.99V, so that's about right on. I'm not entirely sure where to look because 185F is 1.6V if my math is right.

    How about you try (no power connected) measure the resistance between:
    PROBES header 1 to 2: 20kohm +/-1% -- I read 19.8kohm
    PROBES header 2 to 3: 20kohm +/-1%
    PROBES header 1 to 3: 20kohm +/-1%
    ATMEGA pin 27 to 26: 220kohm +/-10% -- I read 215.2kohm
    ATMEGA pin 26 to 25: 220kohm +/-10%
    ATMEGA pin 27 to 25: 220kohm +/-10%
    ATMEGA pin 28 to 27: connected but resistance will climb, starting from 150k but more importantly make sure the reading doesn't start and remain stable
    ATMEGA pin 27 to 24: connected but resistance will climb, starting from about 200k but more importantly make sure it doesn't start and remain stable

    What Ralph suggested with reflashing the AVR, that's from the webui LinkMeter -> AVR Firmware -> Online Repository, then click "Flash" next to the top item on the list, the most recent one. I don't think that will make a difference because you said that the voltages were all the same at the atmega but it is definitely worth the time to try it.

    We might also try resetting the EEPROM of the HeaterMeter to see if it fixes things, like there's some bad data in there offsetting the value. The easy way to do that without losing your wifi settings is to use the same procedure above except select "reset-eeprom.hex". After it flashes, it should say "Clearing EEPROM" then "Clearing EEPROM Done!" on the HeaterMeter LCD. Once you see the "Done!" flash that first image on the list again (the most recent one again) to get you back on HeaterMeter firmware. I don't think this will do anything either, as like you've said, the voltage at all the pins is the same so there's something in hardware going on.

    The fact that it is 185F, which is roughly half the 3.3V pullup voltage makes me suspicious that something is forming a voltage divider splitting the voltage in half from 3.3V down to 1.6V so I think the solution is going to be somewhere in between the jacks and the atmega pins. Worst case scenario, you can always mail it to me and I'll debug the hardware for you. Just email me at heatermeter@capnbry.net if you want to do that.
    I'm that HeaterMeter guy what ruins everybody's free time.

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