MODIFYING THE CX22 TRAKBALL FOR THE ST by Blake Arnold The following instructions explain how to modify an Atari trackball (model number CX22) to work like a mouse for the Atari ST (complete with left and right buttons). To start with, if the instructions here are followed PROPERLY (and you don't fry a chip) it should work just fine, however, I make no claims as to the accuracy of this file, nor do I guarantee that this will work for you. NOTE: This modification will NOT retain the original "trackball" or "joystick" modes of the ball. WARNING: The following ONLY applies to the model CX22 trackball! The CX22 can usually be identified by its case (the case matches the 800XL series computer) which is dark brown on top with a white bottom. When in doubt, flip it over and look for a model number! Things you'll need: * An Atari trackball, model CX22 1 A Radio Shack joystick extension cable (part # 276-1978) 2 A low-wattage soldering iron (15 watt, or close to that) 3 A Volt-Ohm meter (you'll need to trace some wires) 4 About 2 feet of wire (small gauge will be easier to work with, such as the wire in the joystick cable) Before we get into this, if you're not familiar with electronics or soldering to IC's, PLEASE have someone else do this for you. Also, DON'T trust the colors on the wires in the Radio Shack joystick extension cord! Every one that I buy is different (Radio Shack seems to use a random color coding... makes it tough on us guys), so you'll need to trace the wires to see what pin on the plug they go too (thats what the ohmmeter is for). To open up the trackball, remove the 4 screws on the bottom of its "wings"; it still wont come apart after that because there are 2 friction-fit posts inside it (both near the center of the case, one at the top and the other at the bottom), pry it apart slowly and gently to avoid breaking them. Once you open up the trackball, remove the old joystick cable (it doesn't have all the wires we need). Now get your Radio Shack joystick cable and clip off the MALE end and discard it (the end with the metal pins sticking out). In case you don't aren't familiar with the the pin numbers of the joystick cable (the Radio Shack cable doesn't have them numbered, either), here's the layout: Looking at the JOYSTICK end of the cable (female end): 5 4 3 2 1 9 8 7 6 Strip about 6 inches of the outer jacket off to expose the individual wires (you'll need a little length to work with). The only pin we wont be using is pin 5, so trace it first, and clip off it's wire (now it's out of the way for good!). Next trace all the remaining wires to their plug pin numbers and write it down someplace. Look at the IC's in the trackball. Find the one marked LM339 (it's a 14-pin IC sitting away from the other IC's, directly south of where the ball sits). The IC's pins are numbered as follows (standard IC numbering): (looking at the top of the IC) 14 13 12 11 10 9 8 notch --> ) 1 2 3 4 5 6 7 Make the following connections to it: (Plug pin # to LM339 pin #) 1 - 2 2 - 1 3 - 14 4 - 13 Connect the following wires to the connector that the original joystick cable was plugged into (look on the PC board, the connector's pin 1 is numbered). (plug pin # to PC board connector pin #) 8 (ground) - pin 1 (closest to center of the case) 7 (+5 v) - pin 2 (to the left of pin 1) Jump a lead from one connector of each fire-button pad (right and left pads) to pin 1 on the PC board connector (in other words, ground them). Make the following connections to the other side of the fire-button pads (we're going to separate the right and left buttons). (plug pin # to --- pad) 6 - left fire pad 9 - right fire pad Now hook it up to the ST to make sure it works properly. Before you close it up I recommend that you strain-relieve the cord. The easiest way to do this is to tie a knot in the cord where it exits the case (this will keep it from being accidently pulled out of the trackball). Close it up and you're done. Special thanks to Norm Weinress for info on the LM339 pinouts.