[sdiy] Power distribution board

Sat Apr 4 08:31:59 CEST 2009

Don't know the rational behind the MOTM connectors having 2 grounds which 
are the same but I do know that Oakley Modular systems do actually maintain 
these as sperate grounds with one being assigned to the panel ground and the 
other to the actual power ground. This only works if there are no other 
non-Oakley modules in the system (unless they also have split grounds).

It is good practise for the ground tracks to be beefier than the power 
tracks and maybe the MORM system uses this reason. Also there is some logic 
between considering them as 2 separate supplies, a +ve supply with ground 
and a -Ve supply with ground with the grounds commoned together at some 
point.

Best Regards

(Mr) Laurie Biddulph
Phone: +61 (0)2 4340 0938
Mobile: 0400 257 645

Elby Designs
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http://www.elby-designs.com

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----- Original Message ----- 
From: "David G. Dixon" <dixon at interchange.ubc.ca>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, April 04, 2009 5:09 PM
Subject: RE: [sdiy] Power distribution board

> Wow, great replies!  Thanks to all.
>
> I've had a look at Ken Stone's board, and it has six parallel traces: 
> +15V,
> 0V, 0V, and -15V for analog, and then +5V and 0V for digital.  If the
> digital supply has its own ground, then why two grounds on the analog 
> side?
> Are these two grounds ever used separately on individual modules?  (I've
> just wired mine together on the boards I've built so far.)  As the MOTM
> board does not supply +5V for digital (as far as I can see), do they drop
> the voltage level for digital at each module as required, and then reserve
> one of the ground connections for digital?
>
> Also, what is the standard wire gauge to use for connecting the modules to
> the power distribution board?
>
> Thanks in advance!
>
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> 309-6350 Stores Road
> Vancouver, B.C. V6T 1Z4
> Canada
>
> Tel 1-604-822-3679
> Fax 1-604-822-3619
>
> "PERFECTA FINGAMUS SERVIAT NATURA"
>
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>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> bounces at dropmix.xs4all.nl] On Behalf Of Roy J. Tellason
>> Sent: Friday, April 03, 2009 9:53 PM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] Power distribution board
>>
>> On Saturday 04 April 2009 12:20:47 am David G. Dixon wrote:
>> > I've just taken delivery of a Power-One +/-15V, 1.5A power supply, and 
>> > I
>> > need to etch a distribution board for it.  I would like to build
>> something
>> > like the MOTM board with an array of MTA156 4-pin connectors, and I'm
>> > wondering if anyone can point me to a PCB image for something like 
>> > that.
>> > If not, I will have to draw my own, in which case I have a question:
>> >
>> > I ascertain that it is important to connect each ground pin to the 
>> > power
>> > supply ground buss with it's own trace (the so-called "star ground"
>> > configuration).  Is this important enough to justify the inconvenience?
>> If
>> > so, then should one also do the two power rails this way?  Also, what 
>> > is
>> > the deal with the two ground pins on the 4-pin connectors?  Are they
>> > actually different?
>> >
>> > Power distribution seems like a fairly important thing -- I don't want
>> to
>> > screw it up!
>>
>> Having each and every load in whatever system it is that you're building
>> having its own power run to the main distribution point and ground point
>> is a
>> nice idea theoretically,  but not doing so isn't going to get you in
>> anywhere
>> near as much trouble as ignoring this idea completely and letting things
>> fall
>> as they may,  convenient to routing traces and whatnot.
>>
>> I personally would have no particular problems with connecting power and
>> ground to a bunch of modules by way of a number of heavy buses on a 
>> board,
>> though if it'll make you feel better sprinkle assorted bypass capacitors
>> along it,  to deal with whatever bits of noise might end up there.
>>
>> If you really want to get some idea of the effect,  figure the maximum 
>> and
>> minimum current that any given load is going to present to the supply,
>> then
>> figure out what voltage drop these are going to create for a given
>> interconnect,  whether it's that bit of distribution board trace or the
>> connectors you're using (all of which have _some_ resistance) or some
>> other
>> aspect of things.  Having all that info on hand the calculations get a
>> little
>> cumbersome after a while.
>>
>> I suspect that the overall noise won't amount to that much.  I also
>> suspect
>> that some decoupling at the power pins of each module or board will help
>> this
>> some as well.
>>
>> There's also a fair amount of stuff I've seen that ran two sets of
>> grounds.
>> One instance would be a 22 gauge ground lead for something that didn't
>> have
>> much of a current draw,  the other would be an 18 gauge wire for stuff
>> that
>> did,  like audio power amps and such.  This was in organs.  Another
>> instance
>> of separating things out like that is when analog and digital get mixed 
>> on
>> a
>> board,  there will often be separate grounds which,  while ultimately 
>> both
>> of
>> them end up grounded the digital side will tend to have (and even
>> generate)
>> more noise,  which you wanted to keep out of the analog lower-level 
>> stuff.
>> And the old c64 had two separate and distinct +5V supplies,  one on-board
>> and
>> one coming from the external power brick,  the onboard one mostly feeding
>> the
>> VIC and SID chips and not much else IIRC.  (Depended on what version of
>> the
>> board you had too.)
>>
>> How important this is depends on what you're gonna use that PS for.  What
>> will
>> it power?
>>
>> --
>> Member of the toughest, meanest, deadliest, most unrelenting -- and
>> ablest -- form of life in this section of space,  a critter that can
>> be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
>> -
>> Information is more dangerous than cannon to a society ruled by lies. --
>> James
>> M Dakin
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