All pins are crimped with their own individual wires.  Currently, as=20
this has evolved with lots of feature creep the pin functions are all=20
over the place and the wiring harness is hence pretty disorganized.  the=20
only part that's really nicely done is the analog sensor inputs are on=20
it's own harness branch.

But the cable/harness is being redone for this change.  All motor and=20
solenoid signals will be off on one branch, power on it's own, and=20
analog on another branch.  The few (slow) I/O signals should get it's=20
own branch (should because it goes where the power is going, so it may=20
get lumped in with the 12V power and main grounds).

The analog signals are on 10-bit A/Ds and most are getting 30+ samples=20
(some over 100) averaged and filtered.  All of that works well right=20
now.  Yes, I'm thinking the spare pin should be and ground OUT to the=20
analog sensors (and I'm also providing 5V out to those sensors).

Cheers,
-Neil.


On 8/26/2015 9:15 PM, stephen.forrest@agilent.com wrote:
> Hi Neil -
>
> I'd be more concerned with the bundling of the cable - do the different w=
ires bundle together in a single cable? Do they go to one destination? How =
long is it? Any shielding? Is this a ribbon/IDC connector or individual/cri=
mped? Is there another ground path (chassis)?
>
> Also, how much resolution do you expect from your analog signals (I assum=
e 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-=
signal board.  The system has high-current, high-voltage, repeated-switchin=
g 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 on=
e 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, powe=
r supply in the middle (but off towards the back), and 2 PICs that handle a=
ll the logic near the other side.  The analog circuitry is kept really shor=
t 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.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/cha=
nge your membership options at http://mailman.mit.edu/mailman/listinfo/picl=
ist
>

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