[thingstodo]

Originally Posted by MPaulHolmes

I could definitely use beta testers. They should be fine, as it's basically the same thing I've tested. But I passed a kidney stone doing like 10000 different variations of component positions and routes so as to make it a good 2 layer layout, with good ground and power planes.

I would use shielded 7 wire cable like this for the interface:
Buy High Quality RS232 extended distance cable to eliminate signal noise and loss of data

That cable lists one overall shield. I'm no expert .. as I understand signal noise, you are trying to isolate the higher frequency PWM signals so that they are as close to a square wave as possible. The DC on 24V and 5V is likely generated from a switching power supply and could have similar frequencies (depending on the level of filtering).

Our instrument department is *VERY* picky about which cable is installed in our mill. They specify belden cable - I will look it up on Tuesday and post. I'm sure that there is a single shield per pair as well as an overall shield. It is likely more expensive, but having your system work reliably is *PRICELESS*