RE: Interface update

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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