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Normal arcade cabinets run of analogue RGB and composite negative sync. You can get hold of the RGB quite easily, but you need to strip the composite sync of out of the composite video signal.
Looking at the back of the SCART plug (i.e. this is really a TV's SCART socket)
You're interested in the following pins..
2.........Sound Right6.........Sound Left (Mono)
7.........Video Blue
11........Video Green
15........Video Red
20........Composite Video
21........Frame Ground
If 21 (the actually metal) is not connected to ground one of the following pins can be used instead
4... Audio GROUND
17.. Video GROUND
18.. Blanking GROUND
13.. Red GROUND
5.. Blue GROUND
9.. Green GROUND
21 is connnected in all Dreamcast scart cables that I've seen, but you never know!
Simply take the Red, Green, Blue wires and solder them to the correct pins on the JAMMA biscuit. Solder Ground to Video Ground on the JAMMA
biscuit, then solder another wire from that Video Ground on the JAMMA biscuit to another ground pin on the JAMMA biscuit.
Then you have to make up this circuit...
Note: You may not need to make this circuit if your arcade monitor can either
.use composite video inplace of composite sync
or
.you take a feed directly from the Dreamcast's video sync output
The video circuit method will work with all standard arcade monitors, the circuit free version may not
(Click for a more detailed diagram)
...and solder the generated Composite Sync to the Video Sync pin on the JAMMA biscuit. Take the +5V and ground from the JAMMA biscuit. If you
plug in the console you should now have video in the arcade cabinet.
If you'd like more details on how to set the circuit out on a bit of stripboard, click here
Wiring in the Sound
You could wire in stereo sound, but if you do you'll need two audio amps - and stereo isn't JAMMA standard. Put together your audio amp, wire in
the left channel from the scart socket. Wire in ground and +12V to your audio amp (from the JAMMA biscuit), then wire in the output to the speaker
pins on the JAMMA connector. You should now have sound.
Wiring in the Controllers
JAMMA only has an eight way joystick and 3 buttons.
For a Dreamcast you really need a 4 button or 6 button cabinet
6 button cabinets have the extra 3 buttons on a seperate connector, 4 buttons cabinets
i.e. 'NeoGeo' style cabinets
usually just use some of the undefined pins on the JAMMA connector.
i.e. pin 25 (the next pin immediately after 'button3') is used for the extra button
(one button per side of the JAMMA connector)
JAMMA Pinout
The first DC2JAMMA project I made used a 6 button cabinet, the second a 4 button 'NeoGeo'
style cabinet.
To be honest - the 4 button cabinet is just about as good as the 6 button one -
and involves less work.
Even Capcom is now releasing their beat'em ups (most obvious use of a 6 button cabinet)
for DC with a 4 button control system.
Anyway, onto wiring in the pad
Take the DC control pad completely to bits - take every single screw out, remove every piece
of plastic (that is held on with screws !)
You should be left with just the board.
Wiring in the (digital) joystick and 4 buttons (A,B,X,Y) is straightforward, and the same
as the other Console2JAMMA projects on the site - the 2 shoulder buttons are a bit different
After taking the pad to bits - you may start to wonder how the shoulder buttons actually work
They are pivoted pieces of plastic - which have no electronic componets attached to them
whatsoever
The simply move in and out - and that's it
They're actually using Hall Effect Sensors.
Inside the plastic 'trigger' of each of the shoulder buttons is a small magnet
- on the opposite side of the pad's board there are 2 small ICs marked HED5 and HED6.
As the magnets are brought closer to these ICs -
the output voltage of these sensors change - thus giving us an analogue control.
The analogue 'thumbpad' works in exactly the same way - with 4 hall effect sensors arranged
in a cross
So now the big question - how do we possibly wire these analogue ICs into an arcade cabinet
when all we've got is a switch that is either 'open' or connected to ground ?
The answer's surprisingly simple
Luckily for us - the Hall Effect Sensors are wired in so that the more a trigger is squeezed
the more the output voltage tends towards zero
So - all we have to do is wire in our control line to the output pin of the IC.
Now, when a button is pressed in the cabinet, this will got to ground (i.e. zero)
and the output of the IC will also go to zero -
so we've convert the Hall Effect Sensor into a digital arcade button with no
electronics whatsoever
The diagram below indicates exactly where to solder your wires on to the DC pad to wire in
the joystick and 6 buttons - as I've said, if you're only making a 4 button version,
you can ignore the 2 shoulder buttons
The JAMMA pinout looks like this:
Click here for diagram
If you've followed all of the above you should now have a Dreamcast in an arcade cabinet. The easiest way to do it is probably Controllers first, then sound and video.
If possible, just wire up the start button, joystick and a couple of buttons for one controller. Then plug this into your arcade cabinet, but don't turn the thing on. Then plug the Dreamcast into a TV as normal, turn the Dreamcast on and see if the arcade controller works; if it does wire in the rest of the player 1 controls, check it, then do the same for player 2. If it doesn't work then just check all the wiring for loose connections/shorts. Then wire in the sound, check that (you need to turn the arcade cabinet on this time), finally wire in the video.
Good Luck