Re: Interface update

Doug,
It's real great that you are trying to resolve this problem. I completely
agree that we need some sort of breakout box that could get us up to speed
faster. With an on board 5vPS, relays, screw in terminals and such. It
just so happens that I have already designed a proto type of this board to
work with CNCpro. Except that it does not use optoisolation on the board.
I already have optoisolation on board my step drivers.

The proto type plugs into the parrallel port via cable. It has it's own
DB25 connector on one side and has a series of screw terminals on the other.
It consists of a SN74S244 hex schmit trigger driver to drive the step and
direction data (3 or 4 axis or whatever)into the Step motor drivers. The
auxillary outputs, 3 in all so far (CNCPro at least) go through ULN2003a's
(that can be parralleled for more current) to drive 1amp 5v relays. Also,
the homing inputs are hooked up to IR switches with their own terminal
block. The other inputs are just tied high through 4.7ks. I am still
working on the design and am thinking about making it more universal for
other parrallel port NC programs that aren't as configurable as CNCpro. But
first I'm keeping it simple. I'm sorry for not getting ideas from you guys
but now I have a feeling what you want. Are you sure you need optoisolation
on the board too? I can add them right to the output of the SN74S244 but
then the opto isolators would be driving opto isolators. Maybe I can put a
switch selector to bypass opto isolation if the step drivers have them.

Possible enhancements: On board 5V power supply(otherwise supply external 5v
PS). Connectors to connect 120v to stepper power supply with fuses etc.
Diagnostic LEDs connected to various outputs. Connectors for main power
switch and power light. Oh, limit switch connectors tied to turn off
stepper PS. There you have it! All-in-one wonder board!

About using the parrallel port for drive LED's....you should sink them of
course but it's always better to put a buffer inline like an S series TTL
driver which can source 28ma and sink 64ma perfect for this situation, more
noise resistant and just what their made for. This way you don't have to
worry about how much power the parallel port can provide.

Good luck
Dean

----- Original Message -----
From: Harrison, Doug <dharrison@...>
To: <CAD_CAM_EDM_DRO@onelist.com>
Sent: Wednesday, February 23, 2000 9:31 AM
Subject: RE: [CAD_CAM_EDM_DRO] Interface update


> From: "Harrison, Doug" <dharrison@...>
>
> The idea of building the board as an ISA or PCI card brought mixed
reviews.
> Based on your opinions and some new revelations, I am now leaning toward a
> separate card connected via a DB25 cable. Here are my observations.
>
> 1. The parallel port DB25 is mounted directly to the ATX motherboard.
> Sources tell me the ATX will probably be around for awhile and this is the
> MB we need to work with.
>
> 2. I am under the impression that several of you want to keep your PC on
> the desktop, rather than build it into a cabinet with the amps, relays,
etc.
> A separate card would definitely be better here. Those of us who want to
> build the PC in can still work with the separate card.
>
> 3. The ISA slot is rumored to be on the way out. Not everybody has or
> wants to buy a PCI MB. The separate card will satisfy more people since
it
> does not limit us to a particular class of MB's.
>
> 4. The PC card format was originally chosen because I had a source for
dirt
> cheap DC-DC isolators, which would eliminate the need for an external 5V
> supply. Closer inspection reveals that these converters only have 500V
> isolation capacity. That's not much - perhaps enough for most of us, but
> not up to industry expectations. And I am looking for something
industrial
> strength.
>
> 5. "Keeping the fire out of the box" has some merit.
>
> Some of you have expressed an interest in adding features such as an
encoder
> interface, on-board timer and 8255 I/O. This might be feasible if the
board
> went into a PC slot. Adding these to an external board would necessitate
> something more than a single cable connection to the PC unless we abandon
> the original goal of simply trying to make CNCPro easier to implement.
> Remember that CNCPro relies on the parallel port for all communication
with
> the machine. I believe other software uses this same approach. It is the
> bonehead simplicity of this approach that I am trying to expand on.
>
> What about -
>
> 1. Places for either DB25 or screw terms for the input.
>
> 2. Places for either DB9 connector or screw terms for the step/direction
> outs. Maybe Dan Mauch will do the same for his next amp kit. Neat, Huh?
>
> 3. On-board 5V supply for the optos, with an output to fire SS relays.
> Just hook up to 120V and connect the cables.
>
> 4. Maybe even a few spots to install optional SS relays on the board.
> Populate as needed.
>
> Am I getting warmer?
> Doug
>
>
> > Suppose I design a card that will fit in one ISA or PCI slot that has
> > optoisolation, 5V isolated supply for outputs and a screw terminal strip
> > that sticks out the back for direct connection to amps, switches and aux
> > I/O. No interface cards to make, no pullup resisters to find a home
for,
> > no
> > breakout boards to buy, no 25 pin DIN connectors or cut-to-length serial
> > cables to fiddle with. Just connect the amps, switches and I/O to the
> > back
> > of the PC and go.
> >
> > I am working on a prototype of this board and plan to build at least a
few
> > of them for my own applications. A little profit from the sale of such
> > cards would be nice, though that is not my goal, nor will it influence
my
> > decision to do the design. At the very least, the plans could be
released
> > to public domain.
> >
> > Questions:
> > 1. Do you see enough demand for this kind of board to justify having
> > 50-100
> > PCB's etched?
> >
> > 2. What functions or features would you add or subtract?
> >
> > 3. Would you prefer a separate (not in the computer) board fed by a 25
> > pin
> > cable? This would require an additional cable from the PC power supply
to
> > feed the 5V isolator.
> >
> > 4. I have selected a few candidates for the optocouplers and a shottky
> > driver to feed them. However, component selection is not my area of
> > expertise (I'm not sure what is). Can somebody recommend components
that
> > will give a good clean pulse at 100khz? Perhaps a good representative
> > circuit?
> >
> >
> > I eagerly await your humble opinions.
> > Doug Harrison
> >
> >
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