Re: Simple question about cleaning up ground line

Half a volt of noise won't mean squat to a relay with 5 volts across the
coil (a couple of volts MAYBE). Plus "noise" (a microsecond here, a
millisecond there) is going to be ignored by the relay. Don't forget to
put a diode across the coil. A capacitor wouldn't hurt either.

To make the board work without the relay you could try a capacitor from
the EPROM line to ground ON THE BOARD. About 10 uF should do it.

The advantage of the relay is it also keeps static discharge off the
EPROM input.

Andrew Wilson wrote:
>
> Won't I have the same problem (noise on the switch gnd line causing the
> relay to open/close)? Or is the relay automatically more resistant to noise?
>
> -atw
>
> ----- Original Message -----
> From: "Rodger Boots" <rlboots@cedar-rapids.net>
> To: <rasterlist@synthcom.com>
> Sent: Saturday, March 30, 2002 3:07 PM
> Subject: Re: RASTER: 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 15:32:12 2002