First of all, you have to separe the digital signals in one connector and
the power signals in the other connector.
This is the first rule.

If you have analog signals as well, use the third connector, or just put
them in the opposite corners of the digital connector with plenty ground
between them.

Power connector should have at least one large capacitor onboard near it,
but I suggest to mount one for every strong current (ie. solenoid, motor).
There should not be any reverse spikes on your board, use diode suppressor
mounted on the solenoid coil ends and not on the board.

You may split the ground, but this is not enough if you don't split as well
the power supply lines, even it comes from the same power supply.

best luck,
Vasile

On Tue, Aug 25, 2015 at 9:55 PM, Neil <picdude3@narwani.org> 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.
>
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