Hi Neil -

I'd be more concerned with the bundling of the cable - do the different wir=
es bundle together in a single cable? Do they go to one destination? How lo=
ng is it? Any shielding? Is this a ribbon/IDC connector or individual/crimp=
ed? Is there another ground path (chassis)?

Also, how much resolution do you expect from your analog signals (I assume =
you will digitize). What is the source impedance? Amplitude? How many?

I personally would associate any spare ground with the analog signals.

Good luck!
Stephen



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of=
 Neil
Sent: Wednesday, 26 August 2015 4:55 AM
To: Microcontroller discussion list - Public.
Subject: [EE] Best practices for reducing noise

I'm trying to figure out how best to allocate connector pins for a mixed-si=
gnal board.  The system has high-current, high-voltage, repeated-switching =
signals (motors and solenoids), serial data signal pairs, and a number of a=
nalog 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 th=
ose 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 se=
parate from the motor/solenoid side?
- Anything else I should do?

Cheers,
-Neil.

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