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Can I cable a GRBL Arduino to the parallel connector of my CNC controller?

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vtsteam:
For the electronics experts out there -- I recently lost the second of my two ancient parallel ported laptops, used for LinuxCNC. No more parallel port computers suitable for the small space and very occasional CNC use.

So I decided to go to GRBL since I have a bunch of Arduino UNOs. I flashed one with GRBL, and then opened up the existing CNC controller, which consists of the usual breakout board, plus individual stepper drivers, and a power supply.

I first thought I'd replace the breakout board with the arduino, but rather than disturbing the existing wiring and parallel port setup, I am now wondering if I can just feed the Arduino's signals through the existing parallel port by using an existing parallel cable, cutting it, wiring to the Arduino, and plugging it into the existing controller?

I do know the pinouts for both the GRBL'ed Arduino, and the Centronics connector on the controller (ie, step direction, limit switch, etc.). I'm just wondering if the signal levels and isolation are compatible. I'm guessing (you would know better) that there are isolators on the breakout board in the controller already.

Well pictures are worth a thousand words they say, so here are a couple of the whole works, and the breakout board/parallel port:

(Thanks in advance for help!)

 

  

 

BillTodd:
 Are the arduios 3v  or 5v ?  Are the optoisolators compatible with the  Arduino I/O?

vtsteam:
Hi Bill, the Arduino is a bog standard Arduino UNO, which as far as I know runs on any power supply between 7 and 12V, and can supply 5V as a source.

In GRBL setup mode, as far as I know, it can be direct connected to stepper drivers like the 3 boxes in my control unit without any opto isolators.

I've just taken a flashlight and a magnifying glass to the parallel port breakout circuit board and all the opto-isolators are a type 817S.

 

vtsteam:
Well I'm going to rush in and tread where.... um I'm impatient....  :zap:

Okay so the first question is, are the opto-isolators going to be overdriven by the Arduino's outputs?

Let's say the Arduino is putting out 5V -- the 817 optoisolator can handle anywhere from about 5ma to 50 ma.

So I could hook up a variable power supply to one of the step or direction pins and slowly crank up the voltage from zero and see what the current draw is as I go, not to exceed 50ma. If I reach 5v, then I should be good to go on the step and direction pins. those are inputs

The switch pins are outputs and those are TTL level. I'll have to figure that out later. Right now I just want to get the steppers moving.

BillTodd:
OK according to wiki Arduino UNOs are 5v so that's good .

Looking at the break-out board there appear to be resisters inline with the opto-isolators so , again , good.


The opto outputs (back to the arduino will probably need some pull-up current which should be supplied by the pin or a resister on the BO board.

Wooden legs are cheap.... so go for it

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