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Postby jtb223 » Mon Dec 18, 2017 4:21 am

I shut down all of my limit/home switches and it looks like it's working again. I had a problem with one of these switches a while ago and I replaced it. Maybe I'll look into proximity sensors.

Anyhow, thank you for you excellent support. You have some great products and unmatched support.

I hope you enjoy the holiday season.

Thanks again,

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Postby cncdrive » Mon Dec 18, 2017 10:54 am


You are welcome. It is good to hear that we figured the root of the problem.
To now debug where the noise spike comes from is unfortunately mostly not as easy as figuring out what we figured out so far.
It can be from several sources:

- If you running a VFD with a powerful spindle motor then it is possible that it emitting noise which effects the wiring or BOB etc. It can be that the noise is transfered via the grounding if the ground wiring of the VFD, PSU of the BOB (if any) or if it is grounded at any point is not optimal, if there are ground loops ... or it is also possible that the wiring itself picking up the noise, e.g. if a high voltage high current wire runs together on a long distance with low voltage wires (e.g. limit input wires).

- If you using a chinese breakout board then it is possible that it is poorly designed. I saw a few of them where the manufacturer used buffer ICs without placing decoupling capacitors close to the chip and with high pullup/pulldown capacitance without any RC filtering which things all makes the system more and more noise sensitive. So, it is possible that the breakout board itself it picking and "amplifying" the noise.

- It can be also a malfunction of a limit switch, when it triggers when it does not have to. E.g. if the spring is broken in the switch or a half-broken wire or a half-broken connection to the switch or to the BOB.

It is usually not easy to get to the root for noise and wiring problems. Even measuring is not very easy, because you need to have a scope or logic analyser with trigger and capture functions and even if you will trigger it that will probably not give an immediate and clear answer to how the spike is generated. But mostly doing more measurements and checking through the whole system offers the solution.
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