Simple question about cleaning up ground line

I have a problem that's almost embarassingly simple.

I just finished up hacking my Gauntlet board to run both Gauntlet and
Gauntlet II (basically, a bunch of the roms are replaced with double-sized
roms, with the high address line attached to a switch that toggles between
+5v and GND).

So, essentially I have a circuit like the following:

+5V ----/\/\/\/\/\-------X----[switch]----GND
              10k ohm

'X' is where I've attached the high address lines from my ROMs. This works
great - when the switch is open, X is at 5V, and when the switch is closed,
X is at GND. I've got this wired up so [switch] is actually the test switch
for my JAMMA cab, and it works nicely.

The problem is that the test switch on my JAMMA cab shares a ground line
with the control panel. When I press buttons on the control panel, it's
apparently introducing a little bit of noise into the ground line, causing
the game to crash sporadically (since the high address line for the ROMs
isn't remaining at a stable ground value).

I'm trying desperately to remember my late-80s college electronics - I
*think* I can put a capacitor in this circuit somewhere to smooth out any
noise on the GND line. I'm guessing that putting it between X and ground
should do the trick (it'll act as if it's debouncing the [switch] to smooth
out any momentary spikes in the ground line) - is this correct? What's a
good value for the capacitor (I'm thinking something like .1 microfarads,
which gives me a RC time constant of 1 sec).

Am I on the right track?

Thanks again,

-atw

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Received on Sat Mar 30 14:22:11 2002