On Wed, 2009-06-03 at 18:22 +1000, Erik Christiansen wrote:
> On Tue, Jun 02, 2009 at 08:04:00PM +0200, Michael Buesch wrote:
> > The AVR certainly is good enough for non timecritical tasks like tool 
> > changer I/O.
> 
> A tool changer looks like an event-driven application, to me. I don't
> know if this site is then of any interest:
> 
> http://github.com/geekscape/Aiko/tree/master
> 
> Admittedly, if I ever reach the point where I'm adding a tool changer,
> I'd probably go with the state machines which I've used for quarter of a
> century. (Telecommunications products often use many intercommunicating
> state machines to rapidly process inputs in a stateful manner, in real
> time. The language used is clumsily named "Specification and Description
> Language", but is very powerful.)
> 
> Erik

I prefer to have EMC2 do as much as it can. If I understand the term
"state" correctly, I would just use parport I/O and handle the logic in
a hal component. For the rest of the machine, I've gotten away with
software signals, but in this particular situation I need to have a fast
hardware PWM signal. I could use a Pluto-P or something similar, but for
just one signal, it's over-kill. Ideally, I would have a $20 board with
an SPI input and a PWM output, which I could use where ever it's needed.
Then not worry about, when I upgrade the rest of the machine to a
grown-up I/O controller. This ST L99H01 seems to fill the bill:
http://www.rutronik.com/index.php?id=939 

but I don't know if they are available yet.

A micro-controller can also be a cheap solution, but the problem is that
they can also do a lot more, so it's tempting to add more features and
lose the original intent. 

Another rambling thought, is that you could have these $20
micro-controller boards that you plug into a socket and turn them into
whatever function you need at the time. I think this is what the Arduino
is about. I suppose this is just a matter of creating an EMC2 "hardware
comp" application. The card could have a few EMC2 terminals that connect
to a parport (for SPI), a few machine side terminals, then a USB port.
You plug the board into the PC's USB port, a window pops up, you press a
button to select the function you need, and presto, you have an ADC
input, fast PWM output, fast encoder input, or whatever you need that
the parport can't normally do. The problem here is that there is no good
way to handle all the machine side signal conditioning and still keep
things simple.
-- 
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/index.html
California, USA


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