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I am trying to shield the cabling on my CNC mill. The motors, unfortunately, do not have connectors but instead have wire leads coming out from the motor housing. I can cut those wires about an inch from the motor and directly solder to the shielded wire, but will this 1" or so of exposed wiring defeat the purpose of shielding the cable? Unfortunately with the length of the cable I can't really slide the shielded housing up over the exposed wires without damaging the cable.

The primary goal is to reduce electrical noise which is causing false reports by limit switches (which is being addressed with an optoisolator / capacitor combo).

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    \$\begingroup\$ Your attention is probably better spent on making the limit switch circuitry more immune, as there may be other sources of interference beyond the stepper motors. \$\endgroup\$ Dec 4, 2018 at 15:22
  • \$\begingroup\$ Yes - I am working on the limit switch circuitry as well, but they only false report when steppers are running. \$\endgroup\$
    – hahnpv
    Dec 4, 2018 at 18:01
  • \$\begingroup\$ That shows they are unsound. Today it might be the steppers. Tomorrow it might be the welder with high frequency arc start installed beside the machine. If they are especially susceptible to the steppers, that might be an issue like poor power supply design or having the encoder signals run parallel to the stepper leads. \$\endgroup\$ Dec 4, 2018 at 18:12
  • \$\begingroup\$ Of course they are unsound - I am looking to solve the problem from both ends, both the culprit of interference and positively identifiable sources of interference. \$\endgroup\$
    – hahnpv
    Dec 4, 2018 at 18:19

2 Answers 2

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1k resistors inline with the signal wires plus 100nF capacitors to ground placed close to the circuit (LTCH1 here) will get rid of spikes coming back from your wires. Crosstalk is common with long wires running together, including low power signals!

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  • \$\begingroup\$ Upvoted for the capacitor, but your answer is more a comment than else. \$\endgroup\$ Feb 20, 2020 at 15:24
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You'd be better pulling new shielded wires for your limit switches and increase the current through your limit switches. For example if your switches are 20mA current loops they will be quite immune to EMI from adjacent cables.

I recommend a circuit like this when using micro switches:

schematic

simulate this circuit – Schematic created using CircuitLab

This type of configuration eliminates switch bounce as well as being very noise immune.

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