LinuxCNC-RIO - RealtimeIO for LinuxCNC based on FPGA (ICE40 / ECP5)

For IO on my boards I used the method Mesa does, FET bus switches with pull up resistors on the “world side”. Granted a bob or other driver is required to interface to the “outside world”, but you have free reign over whether a individual pin is an input or output.
As the original intention was to use Mesa firmware I wanted to be able to interface with their DB25 daughter cards.
Also it quick way to convert an existing parallel port setup. Get the firmware config as needed with riogui, flash the FPGA and plug the existing parallel port bob in and off you go. No changes required to the existing wiring.
Anyway that’s just my take, I know it’s not 100% perfect.

One thing to check with bi-directional chips is the drive, some are only recommended for short distance over pcb tracks, not generally recommended for driving signals over long wires.

That's all great insights and recommendations, thanks guys. And yes, bidirectional translation can skew a signal pretty quick (long traces/wires == parasitic capacitance). Sensitive. Perhaps not ideal for motion control board.

You guys experimented with modern digital isolators yet? Worth looking into or... stick to the medieval optos?

fiber optic cable

i have a 'mikro 5x / amann girrbach' and they use MAX3096 for the encoder Inputs:

±15kV ESD-Protected, 10Mbps, 3V/5V, Quad RS-422/RS-485 Receivers

but not very cheap

Oh I'm serious. Worth ordering a few parts and give it a trial? Looks like proper isolation to me, high speed parts too. Just not exactly cheap though

i think with a universal small controller you should rather look at the price and use the tried and tested

I'm no control motion board expert by any trade. First one. The "Legend" has it that they are noisy and spikey. Mind you I'm having no issue running a colorlight on my lathe which share the same 5V&GND for pretty much everything (rotary encoder, switches, stepper drives, estop, everything basically). Just got isolation on the Spindle/BLDC motor drive (obviously), but that's on the drive itself not on the motion control board. And so I'm a bit lost as to what's best isolation design, low-cost, "convenience-wise".

btw - I apologize for hijacking your thread and abusing your kind generosity (and expertise!!). Just trying to get a semi-universal "RIO Control Board" schematic out for the community to copy/paste and ideally do their own...

Edit: perhaps worth using another forum for those sort of questions?! If so do not hesitate to recommend one/more/many, and I'll be on my way out!!

Just checked my stepper drives and as expected (a.k.a. modern equipment), they do have built-in isolation (optos). Same as my spindle BLDC motor drive, all built-in modern stuff. And so wtf, why the excessive legendary need for so called isolation on those motion control boards for exactly? 

Calling the electron godz lol... 

yes, that's the reason why i only use opto's for the inputs and uln2003 for the outputs. That's perfectly adequate for the hobby sector