Cabinet Tecnical Specifications

Tecnical description of the my arcade cabinet built in the end of 1999.

Cabinet

The cabinet was completely build from scratch, using low cost wood. This is the project, all measures are in cm :

              44       12
       |------------| |--|

    -          ____------+              +-----------------+     -       -
 10 _  ____----          |              |                 |     |       | 20
       |                 |              |_________________|     |       _
       |                /               |                 |     |       |
       |              /                 |                 |     |       |
       |              |                 |                 |     |       |
       |              |                 |                 |     |       |
       |               |                |                 |     |       | 64
       |               |                |                 |     |       | 
       |                |               |                 |     | 170   |
       |                 \____   _      |_________________|     |       _
       |                     |   | 14   |                 |     |       |
       |                    _|   _      |-----------------|     |       |
       |                  _/     _ 12   |_________________|     |       |
       |                 |              |                 |     |       | 86
       |                 |              |                 |     |       |
       |                 |              |                 |     |       |
       |                 |              |                 |     |       |
       |                 |              |                 |     |       |
       |                 |              |                 |     |       |
       +-----------------+              +-----------------+     -       -

       |-----------------|---|          |-----------------|
              62          18                   60

The color is black, with the exception of the upper band that has a transparent plexiglas over the MAME logo retro illuminated.

I used a 21-inch TV with SCART RGB input mounted vertically. This TV (but probably also all European TVs) auto configure itself as a PAL TV if the vertical frequency is lower of 55 Hz and NTSC if greater. So is possible to get two types of different resolutions characterized by a different number of rows. In PAL mode visible rows are 264, in NTSC mode are 224. These numbers may vary a little for different TV, but are approximately corrects. Using interlaced modes is possible to double the vertical resolution, so all possible vertical resolutions are 224, 264, 448, 528. The TV does not limit horizontal resolution, essentially any resolution is possible simply driving the TV with the adequate dot-clock. Using only standard VGA dot-clock horizontal resolutions of 288, 320, 576, 640 are available.

The main limitation is the low number of vertical resolutions, this is intrinsic to the TV hardware. Obviously also lower resolutions are available, but don't cover the entire TV screen.

Output video signal

A normal SVGA board generates the RGB video signal with the correct frequencies for a use by a TV. However this signal require an hardware conversion realized by a simple converter of the synchronization signal realized using the specifications written by Tomi Engdahl on the VGA to TV converter page site.

The only modification I inserted is the 12 V input at the pin 8 of the SCART cable for automatically switching TV to the external input.

I suggest this circuit because is well projected, completely matchs signal requirements, and normalizes the polarization of the sync signal of the VGA output.

Output audio signal

The audio output is the normal headphones output of an old SoundBlaster Pro 8 bit. It's connected to the SCART connector to use the TV speakers.

Controls

Controls are original Happcontrols Ultimate Joystick and Competition Push Button.

Input control signals

Control inputs are subdivided in two category: fixed control, structurally fixed on the cabinet, and removable controls which can be extracted and substituted easily, essentially are removable control panels.

Fixed controls: Commands coin 1, coin 2, player 1, player 2 = 4 (4 unique)
Connectors 9 pin (8 contacts used)
Removable controls, 1 player version: Commands 4 movement, 6 button, 2 generic commands = 12 (10 unique)
Connectors 25 pin (24 contacts used)
Removable controls, 2 player version: Commands 4+4 movements, 4+4 buttons, 2 generic commands = 18 (14 unique)
Connectors 2x25 pin (20 + 16 contacts used)

The 'unique' value refer to the count of commands considering the pair of movements under one axis (left-right, up-down) as only one command because opposite directions are mutually exclusive and is possible to use ghost commands in the generic keyboard hack or keyboard encoder.

This configuration provides the maximum generalization. 2 lines for every command without any common line permit the use of the control by any preferred protocol: keyboard hack, keyboard encoder, joystick interface,... Eventually the contacts my configured as normal-close instead of normal-open simply by using the relative output of the microswitch.

Input coding

All the input coding is based on the hack of an old HP keyboard. The keyboard use a 16x8 matrix, so is possible to use a 16+8-1 = 23 completely independent command whiteout the undesired ghost effect on the used keys. This configuration use a complete column and row, so ghost keys are possible, but only on unused key which can be simply ignored. This work with the assumption that the keyboard when the ghost effect happen generate the keypress event for the real key and for the ghost key, which is the default behavior of keyboards.

All inputs are properly connected for working with the keyboard by a dedicated converter, which realize the properly mapping from command to key. This converter surely depends on the particular keyboard used, and is a simple BIG wiring.

    -----------     25 pin    -------------   25 pin  ----------------------
    | keyboard | -------------| converter |-----------| removable controls |
    -----------               -------------           ----------------------
                                    |
                                    | 9 pin
                                    |
                            ------------------
                            | fixed controls |
                            ------------------

Actually two different converter are used for the two different removable controls (1 player and 2 player) this only for simplifying the first realization.

Problems solved and additional notes:

The keyboard I used has a very strange behavior: the ghost effect is not present when pressing key, but instead is present when directly realizing contacts. So I suspect that a sort of resistance measure is used for detecting a key press.
On some keys also a very high resistance is capable to generate a keypress. For example touching by hands the two contacts.
Cable too long may generate false key press if the respective lines are very near. Probably is a sort of parasite capacity generated by the cable. I'm able to reproduce the problem using a very low capacitor through the contacts. I solved using alternating lines in cables.

Price

These are approximate cost of material used. Not all material was bought, because was reused from other projects.

Item	Price
Cabinet wood	40 EU
Cabinet screws and others	15 EU
Cabinet painting	20 EU
Cabinet wiring	10 EU
Cabinet plexiglas	5 EU
Controls (1 player)	40 EU
Controls connectors	10 EU
Controls wiring	5 EU
VGA-to-SCART converter	15 EU
Total	160 EU	approx. 160 $

Plus the PC/Video hardware get for free:

Pentium 90 overclocked 120
Memory 24Mb
Italian HP keyboard 102 keys
Seagate harddisk 800 Mb
Cirrus Logic video board cl34xx
SoundBlaster Pro 8 bit
TV 21" with SCART RGB input

Plus a LOT of time, two months of my free time.