Here is the control panel as I received it. The control panel
had two joysticks and six buttons per player, plus the one and two player start
buttons. Four of these were missing their microswitches ($0.80 each at Happs
to replace them). Later testing determined that one of the other buttons had a
bad microswitch; I bought that locally for $3.00 (Happs has a $25 minimum
order). I decided on a four button per player layout, and used the extra buttons
for Pause, Menu, and Exit. The extra space from eliminating two buttons per
player would be used for a trackball and a spinner.
Instead of dropping a bundle on a good keyboard encoder, I rummaged through my
scrap pile and found a QTronix keyboard with an integrated 2" trackball.
Testing revealed I could get 18 keys pressed without ghosting,
so I went the keyboard hack route. Since I needed 24 pairs of wires to the
control panel (for the buttons, joysticks, and two LED's), I cut two 25 pin
serial cables in half to use as the wiring harness. One pair of ends is soldered
to the back of the keyboard's circuit board, and the other ends are terminated
in .187 quick disconnects to wire up the control panel. (The switches all had to
be desoldered, as the person who did the conversion had soldered the wires
directly to the controls...) A hole was cut in the back of the keyboard for the
new cables; with the shell assembled, it still functions as a keyboard.
The trackball in the keyboard turned out to be a separate unit once I opened it
up, so I mounted it on a small piece of wood and used 1" plastic spacers to
mount it under the keyboard. It had to be mounted upside-down, so I had to
reverse the axes in MAME when I set it up....
The spinner was made using the TwistyGrip
plans from a Belkin mouse, two aluminim spacers, three nylon spacers, three
fender washers, and a coat hanger. The knob is a solid aluminum 1.25"
"hi-fi" knob that I found at a very old electronics shop; it had been
on the shelf since 1973! Total cost for the spinner was about $20 in parts.
And here's the completed panel! I countersunk the mounting holes for the joystick and trackball so the control panel overlay could go on over them for a cleaner look.
In retrospect, I shouldn't have put the spinner in front of the trackball; it interferes with trackball games too much. As it is, though, it's a pretty workable all-in-one two-player layout, considering the small space to work with.