On Monday, May 18, 2015 at 9:41:44 AM UTC-4, snafu wrote:
On 18-May-15 6:49 PM, Lloyd E. Sponenburgh wrote:
snafu fired this volley in news:5NqdnfiSF-
:

Can I simply swap the E-stop pin configuration to active low and run
the
axis limit switches normally closed (opening when they are hit?

That's the safer configuration, anyway. That way, if a switch fails (bad
contacts, etc), it shows an unsafe condition.

But you really need to find the source of the noise. Feeding the spindle
AND returning the limit switch signals via STP (shielded twisted-pair)
AND routing them so they aren't in _tight_ physical parallel to one-
another is likely part of the solution.

How's the spindle varied in speed -- variable voltage or PWM? PWM is
quite noisy.

"Loading" the E-stop with some significant current will probably help.
If it took (say) a 50ma swing in loop current to cause a signal change,
rather than a couple of ma would likely help, too.

Lloyd



Yep, normally closed is definitely preferred.

The source of the motor seems to be the 12V DC spindle motor. It seems
to trigger the E-stop when it unloads. ie at the end of a vertical
plunge into the work - I'm thinking back emf? Various caps + snubber
diodes tried.

Wiring is well separated but not shielded. I may shield it when I rewire
it depending on what cable I can find....

It's got a 10k pullup at the moment - only 0.5mA. Reducing that is
another thing to try.

Thanks for the ideas.

You _definitely_ want a lower value resistor here. It doesn't take much to induce a half a milliamp of noise into a cable of any significant length. Your pwm(?) motor drive is, as stated before, inherently very noisy.

Just make sure your e-stop switch can handle the load, and that you use an appropriately rated resistor (100 ohm half watt will give you 50mA).