limit switch configuration

[marcelg]

I was wondering if someone could help me?

I build a gantry CNC machine and added limit switches. I wired them NC in series to the input pin (12) one one side the other to +5V of my breakout board. Everything seems great. When I trip the limit switch AXIS displays the limit icon.

The issue is that I'm getting "noise" on the line. HAL scope is showing little spikes. As a result AXIS shuts down with a "Joint 0 on limit switch error". I'm thinking it's because the wire is so long (over 10'). Not being an EE person does anybody know how I can filter these spikes out? I would really appreciate it.

[Al_The_Man]

What break out board?
Al.

[marcelg]

My BOB is the C10 Parallel Port Interface Card

CNC4PC

Thanks

[marcelg]

Could I filter out some of the noise by putting a capacitor across pin12 and 5v.

This might be a bad idea. I grasping

[fmederos]

Hi,
From your description you should have a pull-down resistor at input 12. If there is no pull-down or it is weak (high res.) you will certainly get noise. I did not look at the BOB circuit to check for the pull-down.

If the pull-down is there and strong (say 2Kohm) then you may try the condenser. It may help or not.

In any case you may try twisting the switch cables (independently) and also the motors cables, this significantly reduces noise coupling from motor wires to switch wires. Remember to twist each set of cables independently.

Good luck!

[cncbasher]

also use 2 core screened cable , and ground the sheild only at the controller end to a single ground point

[marcelg]

Thanks for all the help. You guys helped me fix the issue. My breakout board does have a pull-down resister so that is why I was confused about getting so much noise on the line. I'm a bit embarrassed about what the real problem was. Somehow while I was hacking at the issue I burned out the power supply to the BOB. I thought everything was fine because the LED on the BOB was on. I noticed something was funny when the LED would turn off when the computer was off even though the power was still on. After spending $23 on a RadioShack 5volt AC-DC power cable. (They are WAY to proud of those at RS), everything was working fine.

Now I hope that I'll be able to help someone else out next time.