Hummm.... neat question.

One aside: if the connector isn't polarized, you could use strategically=20
place the spare pin such that if the connector is inserted backward and=20
power applied, the +12V goes to this unused pin, and the user gets=20
nothing happening vs. smoke.

Can you arrange things such that you aren't sampling the analog sensors=20
while motors are running (or starting/stopping), or solenoids switching?=20
  Or maybe at least take an average over time to minimize bad data.

Digital I/O ... it would be best if all signals are driven, i.e. not=20
have pullups, for better noise immunity.  Not sure how much it matters.

You could use that spare pin for a ground for digital and/or analog, and=20
have the digital and/or analog ground therefore be separate from the=20
rest, and connect the grounds together where the power comes in from=20
whatever is plugged into this and making the +12V.  That said, I have=20
seen cases where the best performance was to use the same ground all over.

A ferrite on the +12V @ the connector would be a polite thing to do,=20
maybe on the motor as well.  They're cheap.

I assume the serial is differential (rs485?).  Doing it packetized with=20
a CRC and having both ends of the communication keep count of how many=20
packets are damaged is a good way to monitor signal integrity.  i.e. do=20
things all command/response style and be able to ask that count to=20
determine % damaged.

I look forward to this thread!
J



Neil wrote:
> I'm trying to figure out how best to allocate connector pins for a
> mixed-signal board.  The system has high-current, high-voltage,
> repeated-switching signals (motors and solenoids), serial data signal
> pairs, and a number of analog sensor signals coming in.  The catch is
> that this board has only one 30-pin connector (3 rows of 10 pins each).
>
> Currently, I have, in order starting from one end towards the other:
> - Motor + and - (12V, 6A max)
> - Solenoids (up to 4A, but with reverse spikes will see 30V+)
> - Power & ground (12V)
> - Serial signals (3 pairs)
> - Digital I/O
> - Analog sensor signals
>
> The PCB has the motor and solenoid drivers on one side of the board,
> power supply in the middle (but off towards the back), and 2 PICs that
> handle all the logic near the other side.  The analog circuitry is kept
> really short and off in one corner of the board nearest the end of the
> connector with those signals.
>
> So what I'm wondering is:
> - Is there a better way to organize the signals on the connector?
> - I have one spare pin -- should I run a separate logic ground?
> - If so, where would I connect these on the board (or wouldn't this
> cause a ground loop)?
> - If I do or don't, should I split the ground plane so the logic side is
> separate from the motor/solenoid side?
> - Anything else I should do?
>
> Cheers,
> -Neil.
>
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.