From: sandhoff@csus.edu (John F. Sandhoff)
Subject: Vectrex controllers how-to
Originator: sandhoff@syscube.ccs.csus.edu
Keywords: controller, wiring
Organization: California State University Sacramento
Date: Mon, 27 Jul 1992 18:34:05 GMT

Since the how-tos of Vectrex controllers seem to be a popular topic
right now, here's some 'hardware hacker'-type info.

The joysticks in the Vectrex are configured differently than the
more-common resistor-capacitor network found in most game controllers
(such as Apple II and IBM). In the R-C style the joystick is simply a
variable resistor with one end going to Vcc and the other hooking to
the game port circuitry. In such an arrangement the maximum value is
relatively critical - too low and you don't get full stick travel, too
high and you hit maximum travel before running out of physical range.
Centering is thrown off, too.

The Vectrex connects the ends of the potentiometer to the +/-5 supply
rails. Thus, the voltage fed back to the control circuitry is zero
at center position and varies towards +5 (or -5) as the handle is moved.
(Actually, the voltage limits are about +/- 2.5 volts into the Vectrex.
The joystick is a 10k unit, with a 4.7k resistor on the -5 end and a 10k
trimmer to adjust proper centering on the +5).

Current draw from the joystick is minimal as it feeds the inputs of a
CD4052 switch. Thus, I imagine most any reasonable value joystick will work.
Place a resistor equal to HALF the joystick's resistance in the -5 lead
and a trimmer pot EQUAL to the joystick's resistance (set to mid position)
in the +5 lead. Adjust the trimmer to obtain 0 volts output when the stick
is centered.

Now, you're probably grumbling "Fine, fine. But what are the pinouts?!".
Got a pencil handy? Here they come:

Pin   Function                      Pin   Function
 1     Button 1                      6     Y joystick (wiper of pot)
 2     Button 2                      7     +5 in - to pots via 10k trimmers
 3     Button 3                      8     Ground - common to all buttons
 4     Button 4                      9     -5 in - to pots via 4.7k resistors
 5     X joystick (wiper of pot)           Buttons are N.O., joysticks are 10k

I think I've provided enough info to understand the circuitry, but
if you want a copy of page 17 of the manual (the controller schematic)
I've made it available on the csus.edu Anon-FTP server (/pub/vectrex/pg17.*)
where two versions are available: pg17.tif ('compressed TIFF' format as
created by PC Paintbrush and tested on a NeXTstation) and pg17.ps (converted
from TIFF using Sam Leffler's tools; it prints great on an HP IIIsi). I
can't easily scale the image and it's scanned at 300 dpi so it's only going
to be of benefit to those of you with the proper resources. Sorry...

I'll try to get PBMPLUS compiled and create a GIF image too, but no promises.

If you can't FTP, send me a brief mail message, subject line something like
"Vectrex controller", and 1) your E-mail address and 2) format you want
(tiff, gif, or both). I'll send a uuencode file (247k for tiff and 2614k for
PostScript) right back (Actually, I'll uusplit then before sending and
yes, the postscript os over 2 MEG!)

I've taken apart a Gravis PC GamePad with the intent of modifying it for
the Vectrex. This controller has 4 buttons and a 'digital joystick' that
signals off/on only (hard left, hard up, etc - no granularity). By ripping
the guts out it'll work fine - I'm trying to create an external converter
that you can just plug this unit into but it's going to be cheaper to just
hack a controller up. Gravis also is using a trick I played with years ago -
a 555 timer IC that turns the fire button into a rapid-fire device. The
mods are straightforward for anyone with some experience holding the correct
end of a soldering pencil, and the controller can be found for $20! (Heck,
if you're willing to spend $25 you can get it at Best Products). I'll keep
the list informed.

And thanks to the prodding and info provided by Mark Woodward, I'm actually
getting back to work on fixing up the archives. My evenings are shared
between my family, my '68 Datsun Roadster (which is still a long ways from
running), the Vectrex archives, and my bed. The bed usually loses. :-).

-- John

    John F. Sandhoff, University Network Support
      California State University, Sacramento - USA
        sandhoff@csus.edu

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