newbie wiring help?

Hi,

I have some issues with wiring on my cnc and was wondering if some more experienced guys could step in. I have searched around and found a thread with similar issues but I still have a bit of a hard time wrapping my head around current source vs sink arrangement:
linuxcnc.org/hardy/lucid/index.php/engli...tle-assistance/reply

I have my cnc wired with similar hardware, ZP5A-int breakout board with 2m542 drivers. I have been running mach3 but just built a machine yesterday for linuxcnc (10.4) which im going to set up over the next few days (6000ns latency so far without any tweaks) and ditch mach forever.

Initially I set up my breakout to source current to the drivers as in the first image attachment and things seemed fine at first but missed steps are common so I now believe that my BOB can't source enough current to drive the driver optoisolator inputs on my 2m542 drivers correctly so want to move to current sink as per this thread (although i'm having difficulty wrapping my head around this arrangement)


as per what I have read here (thanks by the way) but a few things are unclear and marked on the second image. If someone could help me i'd appreciate it very much, looking forward to ditching windows permanently.


thanks and regards

My current wiring:





Proposed current sink:

Thanks Andy,

Do you know if the XN, YN, ZN etc can be left unconnected? As far as I know these are ref to GND on the breakout board.

I had a look at the BOB IC's, 74HC244D on the output side, data sheet gives 7.8mA max and driver optical isolator inputs require 16mA max so definitely underpowered for current sourcing as I have it set up now.

I've been toying with the idea of putting a ULN2803 on the output side of the BOB to sink current for the optical isolators, I have these in stock and re wiring would be minimal and could probably be point to point (8 ins 8 out Darlington array

Thoughts?

I was thinking that earlier but wasn't sure how necessary the schmitt triggering was in the chain to "square up" the parallel port outputs, might give that a shot soon or wire my own custom BOB at some point. I have a parallel breakout with screw terminals for each pin so trying it out would be simple enough.

I just found some logic level Mosfets in my bag of tricks (uln2803 weren't behaving) so I think I'll use those to gate the GND side of the drivers opto-isolator inputs and wire the other side directly to a dedicated 5v psu, saves me disrupting the current wiring too much as I can still use the BOB outs to source to the mosfet gates which I can put in between. They're pretty quick devices (90ns rise, 32ns fall) so should be ok and are rated for 30A so won't stretch them in the slightest.

I'll knock up a small circuit tomorrow and so how it goes, thanks for the help, much appreciated!