Hello,
I'm having a problem with my bbq controller where 1 of the 4 inputs intermittently picks up noise. I've been running it with the RTD probes just reading room temperature and about once a day at a random time the temperature rises erratically about 30F degrees. I have the RTD in series with a resistor for a voltage divider between 0 and 3.3V. I've tried multiple different RTD probes. It is always the same input. Could it be picking up static? I think one time when I saw it happening real time I was able to touch the RTD probe and it went back to normal. What could I add to the circuit to discharge any static voltage if that is what it is?
This is what it looks like when it happens:
I also wanted to ask if there is a way to trend like my screenshot but with a generic program loaded to my photon? Goal would be to eliminate the possibility of any issues with my code. If I loaded tinker to it could I some how trend the analog inputs easily?
Is it Photon 1 or Photon 2? And which pin is affected?
It is a Photon 1 and it is input A5.
That's unusual. A3 and A6 have a slightly different circuit because they're also DAC pins, but A5 should be like all of the other A pins.
A hardware solution is probably best, but personally I would fix it by finding an appropriate filter algorithm. Aside from not having to add circuitry, if there are other scenarios where you get invalid samples you can adjust the filter parameters in software.
I think I had it on one of the DAC pins a while back and damaged that input on 2 different photons so I moved it to A5 to get away from the DAC. I have no idea what damaged it as I've been using it that way for years and both were damaged months apart. I guess that could be related.
As for a filter the noise sticks around long enough that it can't be filtered out. It just hangs out at a different value for sometimes an hour. I've modified my code so I am not trending the raw analog value to isolated it from my other code and I'm seeing it there as well. Because it is an RTD, when the temp rises artificially, the voltage on the input is actually dropping since that is how the RTD affects the voltage divider.
That is an odd failure mode. It certainly could be a hardware failure, especially if a nearby pin was damaged.
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