Re: [Emc-users] Encoder as MPG over serial?

[Colin K. <cki...@gm...>]

I'm starting up a blog at http://ckcnc.wordpress.com to document what I'm
working on. There's nothing much there yet but there will be more over the
next couple weeks. I've got all the pieces working, what I need to do know
is tighten everything up. I'm designing a board that will have two encoders
(MPG and Spindle/FRO) and switches for axis and scale selection, continuous
feed, and cycle start/pause/single block, plus maybe a few extra depending
on what I can squeeze in.

What I'm playing with right now is adding an LCD display that could act as a
remote DRO, which would be really nice to have on a pendant. It's tempting
because a 20x4 display can convey a ton of information with 6 output pins
from the Arduino. But, I am running tight on pins as it is, and I feel like
I'd prefer to have hard LEDs for things like the axis and scale selections,
rather than forcing people to read an LCD. Of course, a Max7219 -segment LED
driver gives me 64 outputs from 3 pins, so maybe if I can get both to
work.... more power!

But I'm also unsure about how much data I can reliably push through the
wire. I can do all the core stuff with single-byte messages very easily, but
a DRO message requires 7 for a value like X12.345 (using ASCII), and it gets
messier if your messages have different lengths. So I'm just not sure how
far I am from running into contentions between, say, HAL pushing position
updates to the DRO, and the MPG wanting to move the axis. In principle
there's plenty of bandwidth at slightly higher speeds like 19200 or
57600bps, but my sense is these can be sufficiently less reliable that I'd
prefer to be really conservative, especially if I start selling the board.

Anyway, for your hacking in the meantime, my main suggestion is to build the
stack up in stages like this:

- Write your Arduino sketch with one or two inputs and outputs. Test it with
the serial monitor until it's doing exactly what you think it should.

- Write a minimal Python program you can run from the command line, and make
it talk to the Arduino, again using the serial monitor to verify everything.

- Add the HAL component to the Python program, and test it from the command
line with halrun to verify it's setting pin values as you expect.

- THEN, and only then, link it up with your GUI of choice.

Basically, my experience was that the vast majority of my problems were
actually in getting Python and the Arduino to communicate as I wanted.
Getting Python to communicate with HAL was almost trivial.

Colin-
> Your post was quite timely for me as I just recieved an Arduino with the
> intention of creating exactly the same setup for my gantry router. If you
> could
> share your code it would be a tremendous help and quite possibly save me
> from
> having my head explode. :)
>