"No Pit Probe" above 450 Degrees?


 
M

Mark Swift

TVWBB Member
Hi Guys,

After finally getting my HM Thermocouple version working, I seem to have an issue whereby "no pit probe" is displayed above roughly 450 degrees. If I leave it and it drops below it comes back alive again. I've checked all joints etc and they seem correct, it's also spot on below this temperature!

Any help would be appreciated.

Mark
 
Around 450F is where the ADC for thermocouples switches from the internally generated reference to the external reference. I'd check your AREF and AVCC pins for the proper 3.3V at the atmega (pins 20 and 21).
 
Bryan Mayland said:
Around 450F is where the ADC for thermocouples switches from the internally generated reference to the external reference. I'd check your AREF and AVCC pins for the proper 3.3V at the atmega (pins 20 and 21).
Click to expand...

Hi Brian,

I've checked and it appears I'm not getting a reading at pin 21?
 
I am really not sure what is going on. To be clear, you mean 450F not 450C right? Do other probes (thermistors) work at all?
 
Bryan Mayland said:
I am really not sure what is going on. To be clear, you mean 450F not 450C right? Do other probes (thermistors) work at all?
Click to expand...

Apologies, I mean 450F... The thermocouple works fine until circa 450, and the other 3 jack probes seem to work fine (albeit I have not tried them above 450!)
 
I've gone over the code and I am really not sure what is going on. What you can try is installing the hm-noise AVR firmware then watching the homepage as the thermocouple transitions across the 450F mark. The noise graph numbers should go up until they get to 1000, then it *should* flip to about 333. If they don't maybe that will give us more of an idea what's going wrong.
 
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