PMDX is in the process of designing an I/O expansion board
to work with our SmartBOB series controllers for Mach4. We
would like to know what mix of features makes the most sense.
If we set the number of I/O points as 24, how many should
be inputs and how many should be outputs? These would be
fully conditioned signals, so doing both on the same pin
is not practical cost wise.
We are expecting to have inputs that are more or less universal.
They would work with contact closures, 5 volt logic signals,
and sinking (NPN) or sourcing (PNP) sensors.
The output signals will be more dedicated in nature. The types
under consideration are:
1) Electronic sinking only and rated for 5 VDC to 25 VDC with
a current rating of 500 milliAmperes.
2) Electronic sourcing only and rated for 5 VDC to 25 VDC with
a current rating of 250 milliAmperes.
3) Electronic with selectable sinking (NPN) or sourcing (PNP)
that work with 5 to 25 volts DC with a current rating of
250 milliAmperes.
4) Relay outputs with normally open contacts rated at 5 amperes.
5) Relay outputs with SPDT contacts rated at 5 amperes.
6) Light duty Solid State Relay outputs rated for 100 mA AC or DC.
7) Medium duty Solid State Relay outputs rated for 2 amperes AC only.
The output styles above are listed more or less in order of increasing
cost to implement. In general, outputs are more expensive than inputs.
How important are signals that are isolated from each other as well
as from the controller? This will require two terminals per signal and
will therefore increase costs. Are signals that are isolated from each
other more important for outputs than for inputs?
Would it be better to keep this I/O expander simple and offer a different one
that is an adapter to connect to Opto22 style module racks to accommodate
more diverse needs?
Comments on other considerations not mentioned above are also welcome.
Your feedback and the reasoning for it will be appreciated.
Steve Stallings
www.PMDX.comPS - The snow here is NOT delightful. Over 21" and still coming!
