Although simple in theory and fairly easy to do when designing & wiring
up something from scratch (once you've got it clear in your head what
grounding scheme you want to use), it can be very tricky to change or
improve the factory's grounding scheme on these arcade games... largely
because much of the grounding scheme is set in concrete by the various
PCB layouts.
A bicycle wheel as Matt suggested is a good example of a simple star
grounding scheme and single power source (hub). But what I had to use
with the Asteroids, for instance, is a tree having 3 main branches off
the trunk -- each main branch representing one of the power sources
(10VDC, 72VCT, or 65VCT). As Matt said about the wheel hub, likewise in
a tree, you wouldn't want any branches growing horizontally into some
other branch... thus each power source is tied to the chassis (trunk) at
only one spot.
Remember that we're speaking logical (functional) grounding layout here,
not physical grounding layout. Confusing the two makes things VERY
confusing! Eg. physically, I've got the end of a branch (65VCT power
gnd) floating in a hollow of the trunk (but isolated from it), with the
other end looping way out then back around to connect to the trunk
(chassis) for real. Two other branches (10VDC and 72VCT) are also
floating in the trunk, in another hollow, and both loop way out
separately for awhile, then join together, and connect back to the trunk
with one larger branch. If this sounds like Alice in Wonderland to
you, you're not alone.
From each main branch off the tree (power source), you'll then divide
into small branches, and each of those branches divides into twigs.
In the game, all these uppermost twigs are the circuits on the PCBs
themselves. If you look at a schematic, you'll see lots of little
grounds everywhere.. these are the twigs. Ideally you'd cluster these
twig grounds into local grounds (small branches) grouped by
non-interfering currents, then tie those clusters together into your
main branch, to eventually end up at your trunk (chassis) ground.
In the Asteroids, I could only sort out the main branch grounds. All
the twigs are left alone on the PCBs.
JS
Pat Danis wrote:
> Got it. Thanks for the idiot's guide to grounding. Now I understand
> completely.
>
> Pat Danis
>
> Matt J. McCullar wrote:
>
>>
>>
>> I[Matt J. McCullar]
>> It's really simple. To prevent weird things from happening, just
>> make sure that each major piece of the game has only one ground
>> connection. If you have more than one cable connecting two
>> points, not only is that redundant, but currents can start
>> flowing where you don't want them to.
>>
>> Think of a bicycle wheel with all the spokes. Remove the outer
>> rim so that all the spokes fan out in a star pattern. If we
>> consider the central hub to be our main ground connection, and
>> the end of each spoke to be a different piece of our game cabinet
>> (motherboard, video monitor, etc.), then each spoke has one and
>> ONLY ONE way to connect to ground. If the outer rim were in
>> place, then currents would start flowing between one or more
>> spokes on their own... and we don't want that.
>>
>> I really have been trying to follow this conversation but my head
>> is swimming. Could someone please sum up what they consider the
>> best course of action is in grounding a vector game in layman's
>> terms. ....I knew I should have stuck to my EE major.
>>
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>>
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>>
>>
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Received on Mon Sep 15 11:38:47 2008
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