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I tried searching for this to no avail. I hope I'm not all too wrong asking it here.

I have set up my 60W CO2 Laser with a SKR 1.4 Turbo board and connected a 10k NTC thermistor to measure the temperature of the CO2 tube itself, taping the sensor on top of it.

The problem is that sometimes when the laser fires, the board resets itself - probably due to EMI. When I remove the connection to the NTC, it works fine, further proving this theory. Be noted that it only resets the board sometimes, not everytime. It's probably "just" above tolerance.

Looking near the TH connections, I see some basic filtering circuit, if I'm not mistaken.

TH connectors schematic snippet

(Image source: https://github.com/bigtreetech/BIGTREETECH-SKR-V1.3/blob/master/BTT%20SKR%20V1.4/Hardware/BTT%20SKR%20V1.4-SCH.pdf)

Shouldn't this protect against some degree of EMI?

Is there anything additional that I can do to (further) reduce noise in order to avoid the board reset?

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  • \$\begingroup\$ Use a shielded cable. \$\endgroup\$
    – Damien
    Jun 30, 2021 at 6:19
  • \$\begingroup\$ Foil between the thermistor and laser tube would be a good start; it will attenuate both light and EMP, either of which could be the problem. What physical cable connects to the thermistor? \$\endgroup\$
    – Guy Inchbald
    Jun 30, 2021 at 12:58
  • \$\begingroup\$ @GuyInchbald The thermistor looks exactly like this: amazon.com/Waterproof-Thermistor-Accuracy-Temperature-Arduino/… \$\endgroup\$
    – Fusseldieb
    Jun 30, 2021 at 17:47
  • \$\begingroup\$ OK, if problems persist some cable shielding might help - you'd need to ground it well at the board end only, not the laser end. You could use the same foil that shields the sensor from light. \$\endgroup\$
    – Guy Inchbald
    Jun 30, 2021 at 18:44

1 Answer 1

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Depending the type of your thermistor, especially if its made of semiconductor, a cause could be that the laser light actually goes through the thermistor encapsulant, creating a temporary short when the laser fires.

Some encapsulant are transparent to infra-red, and the famous case of the raspberry pi that would reset when a photo is taken with a flash, is a good example.

You can try to wrap your NTC in aluminum foil.

If the problem is really related to EMI, simply use a shielded cable.

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  • \$\begingroup\$ Thanks for your comment and answer. You have some valid points, however I don't think it creates a short, since it's (already) encapsulated in aluminium. The RPi thing with the flash I've already heard, but it's interesting nonetheless. To shield the thermistor, which are the requirements? Ground it on both sides to the case, or can the shield be left unconnected? \$\endgroup\$
    – Fusseldieb
    Jun 30, 2021 at 17:50
  • \$\begingroup\$ Ground in one side of the cable. What ntc are you using? \$\endgroup\$
    – Damien
    Jul 1, 2021 at 2:50
  • \$\begingroup\$ Ahh, makes sense! The thermistor looks exactly like this: amazon.com/dp/B07RYG8R86 \$\endgroup\$
    – Fusseldieb
    Jul 1, 2021 at 11:20
  • \$\begingroup\$ @Fusseldieb given the NTC is sealed with glue (transparent) on its wire and is an open tube, if the shielded cable doesn't fix your problem, still try the aluminum foil to cover the opening. \$\endgroup\$
    – Damien
    Jul 1, 2021 at 11:47
  • \$\begingroup\$ Which opening do you speak of? \$\endgroup\$
    – Fusseldieb
    Jul 1, 2021 at 11:49

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