New HM build - Thermocouple always off


 
B

Bob Ellison

New member
I just completed the build of my HeaterMeter and had a leftover part - a Vishay 10K 1% thermistor from Mouser. I saw it in the build instructions and thought "why not".

Well this this has taken more time than the assembly of the HM itself (try searching this forum for "thermocouple"). Apologies in advance if this has already been covered "somewhere".

If I set the configuration on Probe 3 to "Thermocouple, mV/C 10000, Offset 0", all I get is an OFF status (with thermocouple soldered in place between pin 1 and 2 and nothing plugged into Probe 3). If I reset the configuration to "Internal", low numbers are presented. I put a ET-73 probe in and it worked fine. I ohm'ed out the the values presented on J2 and appropriate values seemed to be displayed though the thermocouple was a couple orders of magnitude lower than the ET-73.

I set the HM to display the raw values (SP=R): the ET-73 shows a value of ~195000; pulling the probe out to engage the thermocouple reported ~9000 (and bounces around a bit). This value is shown while still using the default "Internal" values. If I switch to "Thermocouple", the display just goes to Off.

I'm using the new v10 build.

Any ideas (other than just cutting the thing off the board ;-)?
 
The 10k thermistor isn't a thermocouple, it is a thermistor! Select "Internal" as the type and "Vishay 10k" as the preset. If you put a probe in, you need to change the preset to the type of probe inserted.
 
Thanks. I should have been more click happy and discovered that on my own.

So, there's thermocouple support. I thought they required some signal amplification (like with a MAX6675 or MAX31855). What are you using? Is it on a daughter card? How do you make a thermocouple "food safe"?
 
Thermocouples do require additional hardware, which HeaterMeter doesn't have. The software is there to do it, with an analog chip such as AD8495. Making the hardware is left as an exercise for the reader! Brian Hilgert I believe has a working model.
 
I have a semi working prototype. I threw my back out to such a degree that I couldn't sit or stand at my solder station for the past week, and before that i was waiting on parts. I hope to get back to it this weekend, but the 'honey do' list has grown pretty long, and a happy wife leads to a happy life.

I don't have a traditional HM board, so i can't test the 'mod chip' on an actual board, but it works on my Mega w/ the latest hm sketch. I'll test it on the grill once my HMX+Pi is assembled, and post the results.
 
Brian Hilgert said:
I have a semi working prototype. I threw my back out to such a degree that I couldn't sit or stand at my solder station for the past week, and before that i was waiting on parts. I hope to get back to it this weekend, but the 'honey do' list has grown pretty long, and a happy wife leads to a happy life.

I don't have a traditional HM board, so i can't test the 'mod chip' on an actual board, but it works on my Mega w/ the latest hm sketch. I'll test it on the grill once my HMX+Pi is assembled, and post the results.
Click to expand...

Thank you very much, Brian.
 
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