Noise issue


John Bostwick

TVWBB Wizard
OK, this one has me stumped.

I am fixing someone board and on the original main board had some issues and I figured I would just re-do the whole board, which I did. I kept the thermocouple Amp, the DC/DC, and some of the other parts. I completely changed out all the resistors and caps. Started up the board and it gives me noise on the thermocouple circuit.

I then put a new thermocouple Amp and still same noise. I checked and rechecked caps and resistors on the thermo circuit and all connections over and over again.

By now, I have replaced all major parts and still same noise and some what unstable thermocouple temperature.

Even when I don't have a thermocouple attached the noise graph will show some noise, but won't show the noise Icon. I also think when the thermocouple has a temp over 100+ it doesn't show noise(i think), haven't really look at when it shows and doesn't.

I tried my wall wart and the one supplied and also different plug ins and nothing seems to change the noise issue.

I really don't know what else to do. Usually, I when I have noise, it's and easy fix of a poor solder joint or so, but I have checked them all numerous times.

So, I come here hopefully some one would post something I haven't thought of yet.


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Ever try a separate different thermocouple?
Yep, tried different thermocouples and even just made a little load on the jack to test and still had noise.

I just gave the board a good soaking in Flux remover, and connected it from my phone into the router and it seems to be running OK now.

Dam, if it was just Flux on the board, I don't how many times I took a vibrating toothbrush with Flux remover on the board as it was, so I guess there was some where the brush could not get to.
When I read this earlier, before coffee, I was wondering what sound could a board possibly make that you could hear.
OK, I just found the reason for the noise, and it has me stumped.

So, I just finished printing a case for it and was getting it ready to be shipped when I reset the SD card back to HM stock and WiFi stock I then turned it on. I then started to experience Noise again. So I connected it back to my WiFi network and checked for noise again, and it was completely gone and the thermocouple is also stable.

The Rpi is a Pi3 B+.
When the Pi is connected to my phone S23u using the default IP it has noise and a unstable thermocouple.

When I have entered my wifi information into the Rpi network page and connect to it through my homes wifi, no more Noise.

Any ideas?

I tell ya I was pulling what little hair I have out this weekend trying to figure out what the hell was wrong with this thing, and now I figured it out and now I have no idea as to why, unless it's some type of ground loop. UT why would the HM know the difference from my phone or my home network?
Does it happen if you move your phone a distance away from the rpi?

What I mean is, does the noise change if you move the phone farther away?
I have chased this noise issue for years. Tried different power supplies, true analog, and different switchers. I have tried with the Pi 3+ the 2.4ghz and 5 ghz wireless bands. Long ethernet cords from outside back into house to connect to my router. Lowest noise I have been able to consistently get was when I use a battery and 5ghz band. The noise is still there but lower and spikes less frequent. If there were more spare parts available and Pi prices were back to 2019 prices, then I would sit down at my bench and continue experimenting to find source. I believe it might be a hardware issue. The next test I would do is to separate the HM electronics from Pi and get a extension ribbon cable, many 2' long, and connect the 2 pieces together with lots of separation and see if this cure problem or reduces noise further. My current thinking is there might be an issue with the 2 different processor clocks and wi-fi radio having a harmonic clash that results in noise. This is a theory, but not tested any further. There are ideas out there that maybe shielded thermocouple cables will help, they can. and do, but the shield needs to be connected to the signal ground of the HM board. I have tried this and did see fair results, but it didn`t eliminate noise.
Brian, others and I spent time looking for source and never really found one. I do know that when noise occurs, it can cause spikes in the control loop. Thats why I use battery power and 5ghz wireless when cooking. This seems to work the best for me. My mesh wireless setup helps with getting a stronger wireless signal for the 5ghz and placement/position of HM makes a difference in signal strength. Wish there was a way to add a external antenna to the Pi to help with Wi-Fi signals. This might help too with noise. Turn off internal patch antenna and connect through external port. The Pi 5ghz wireless connection needs to be really short because of signal strength from my experience.

I'm done. Hopes this helps with your search for the mysterious HM noise.