Hi Tweakie:

I probably did not make it clear where I put the noise suppression.  No, not on the Step and Direction Pins!

My controller has a wire lead header, on the PCB, where you hook the leads from the EStop, Probe, and X, Y, and Z home switches.  Those are the pins that I added the capacitors to.  My EStop is on 15, my Probe is on 10, My X Switch is on 11, my Y Switch is on 12, my Z Switch is on 13.  

Those are all input pins to my controller and are all pulled high with a 10K on board resistor.  It was those wires that I saw all the noise on in the ungrounded condition.

You would think that the low impedance of the 5 VDC Power Supply would be enough to suppress any spikes on the lines, but the 10K pull up resistor raises that impedance and allows the noise to ride along on the wires between the open home switches and my controller.  I have all the wires in a bundle that runs around the machine and go as a group to the controller box.  

Incidentally, I noticed that I DID NOT use shielded wire to the three Home Switches.  That is probably why they are picking up the pulse noise from the motor drive wires.  Same thing on my wire to the Touch Probe.  But I DID use shielded wire to all the stepper motors.  I would bet that if I were to change all the Home Switch and Probe wires to shielded I probably would not have had any noise problems at all.

When operating the mill, the stepper motors are being driven by some pretty high current square waves.  It is easy to understand how much harmonic energy that must be riding up an down the motor leads.  I know that it is impossible to listen to an AM radio in the same area as the mill when it is in operation.

If I get around to it one of these days, I will redo all the wires, using shielded on everything.  I would also separate the input wires from the stepper drive cables, running each in separate bundles.

This stuff is always fun for me to explore.  Hopefully this was a help.

Incidentally, I love your picture.  A flying cat!  I am an airplane pilot and we have three black cats here in the house.

George

Hi George,

Thank you for the detailed explanation for the position of the filter caps - I understand now.
(you should have known better and used shielded wire for your switches  )

I spent over an hour browsing the wonderful pictures of your excellent Zenith build. I think if I had spent 3 years on it I could never have parted with N73EX.

Best regards,

Tweakie.