HeaterMeter 4.2 Thermocouple issue (constantly increases, w or w/o sensor)


 
W

WBHinton

New member
I am a noob. Been a lurker for a long time. Just put together my HM4.2 this weekend, and have an issue with the thermocouple. I did the preassembly amp check and everything was ok. The HM powers up, temp probes work, wifi and web based apps work, but the thermocouple constantly increments the temp up, with or without a type K thermocouple installed. I rechecked the amp with 3.3v as described and it shows good readings. I check the amp with a thermocouple in and I can see the millivolts change when I stick the sensor in my mouth. Then it returns to room temp mV levels when I take it out. When I short the thermocouple jack, the amp reads as it should. I even tried it with a couple different Type K thermocouples. On the webui, sensor one is set to "Thermocouple" the amp setting is 5, offset 0.

I double check my solder connections, reflowed everything around the thermocouple stuff and pulled off the excess with some mesh.

Everything else works on the HM, I have another Type K probe coming just in case that's the issue.

Anyone have any ideas? It feels alot like a software or calibration/initialization issue.
I am thinking about reflashing the SD card.
 
I would test between pin 28 on the ATMega and ground while it is running. If the voltage is stable there when the temp on the probe is stable, then the only thing left that could change the reading is software..... And I would test pin 28 vs the pads under the probe inputs since that is after the resistor/cap network. If the voltage is changing there, then the software is doing what it is supposed to do, and you have a hardware issue...
 
Got it working. I left out the 100k resistor near the thermocouple. I misread the instructions and didn't install any resistors on the thermocouple area. I was too excited about getting it put together I guess.

Marc, Thanks for redirecting me. I would have been chasing white rabbits for along time trying to figure out a software issue that didn't exist.
 
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