RE: New project...PCI based servo control board

[jmkasunich-at-ra.rockwell.com]

Craig wrote:


> GEEZ... I no sooner get my last message and you have it
> designed...:)  I don't have time for a detailed response
> now (I need to do some real work today..:), but with a
> quick read I can say I pretty much agree with your
> thinking.

I've been thinking about this for nearly a year...
This conversation and others in the last couple of
months have really got the gears turning, so what
seemed like a quick response really is the result
of quite a bit of time already spent.

>  I'd like to consider a serial expansion bus.....

I want to stay away from anything that requires
FPGAs, ASICs, or any LSI on the I/O board.  I'm
hoping to keep the tricky stuff on the first
board, and make the I/O board simple enough that
it can be truly open - anyone who can solder can
build it with parts from Digikey.

> But ribbon cable is pretty cheap (if not robust).

My attraction to ribbon isn't cost, it's simplicity.
With all the brains on board #1, the I/O board is
buffers, relays, optos, only - nothing tricky.
There may be better solutions than ribbon, but
the key is many conductors with simple signals
on them.  I agree that a round shielded cable
would be better.  I just took a quick look at
the Digikey catalog - how about SCSI-3 connectors
and cables?  68 pins, and nice shielded cables
are available, as well as less expensive ribbon
versions.  Obviously we would have to make sure
the connectors are labeled - wouldn't want to
plug a disk drive into the CNC port.  Although
if every signal on the cable is 5V or less, you
probably wouldn't hurt anything even if you did.

This is the ribbon version, $13.33 each
http://rocky.digikey.com/WebLib/Assmann/Web%20Photos/AK-Y2301.jpg

Here is the round version, $29.60
http://rocky.digikey.com/WebLib/Assmann/Web%20Photos/AK-Y1301.jpg

Here is the board mount connector, $6.70
http://rocky.digikey.com/WebLib/Amp/Web%20Data/787082.pdf

> Thanks for brain cycles... I will reflect / reply
> more on this more tonight.

I will do the same.  I've had a design in the back of my
head for a step pulse generator, and while walking the dog
yesterday I realized that with minimal mods it could also
become an analog output (pseudo-PWM).  I will draw it up
in block diagram form and post it in a day or so.

John Kasunich