Re: Simple question about cleaning up ground line

Sometimes the "old school" ways are the best. Have your switch control
a relay on the board and let the relay ground the EPROM line. Radio
Shack should have some really nice 5 volt relays.

Andrew Wilson wrote:
>
> 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 15:12:11 2002