The solution is easy. The mouse chip that is probably in your mouse is a Aligent 2610. The data sheet can be found at
2160data sheet . The chip uses a SPI interface. Kronos robotics has an app note on this very subject. It can be found at
Kronosroboticsmouse . From the data sheet Pin 3 is the IO and pin 4 is the clock. You need to find the circuit board traces for these 2 pins and follow them to the USB PS2 interface chip. After you find them, remove the interface chip and re-solder 2 wires to the circuit board as shown in the app note. The mouse I used had a different interface chip. The board was coated. I had to hold the board up to an intense light to see the traces. Next you need to cut the end off the mouse cord and solder on some pins or sockets depending on if you going to use a bread board or the robot controller. This will allow you to power you mouse and interface it to the PIC. I used a Kronos Dios Microcontroller and the code from their site to get it working. The Dios is a Pic microcontroller very similar to the PIC in our robot controller. It is programed in basic. Kronos basic has a software function to send out synchronous serial streams that make the SPI communications easy. They have code examples to get it working. The nice thing about the Dios basic language is that they have high level function to communicate to another micro with ether rs232 or rs485. You could use the Dois chip to interface to the robot controller using Mr. Watson's serial port libraries. The other option is to have the mouse talk directly to the robot controller. While the PIC in our RC has hardware SPI, I believe it is tied up with communications between the 2 PICs in the RC. This means the SPI would have to be done with software or what is called bit banging. Maybe someone on the forum could reference some examples of Software SPI code. While getting the mouse to talk to the RC is doable, I think where this all will fall apart is in adapting optics and illumination to keeping the mouse a couple inches off the carpet . Can an optic system be adapted to the mouse that would maintain focus as the robot bounces around? The chip is also very sensitive to the wave length , Intensity and angle of the illumination. The mouse may be a good replacement for an encoder. Place a wood disk on the inside of the wheel and mount the mouse as close as possible with out touching. The programing could be easier as it wouldn't have to deal with interrupts. The possibility of replacing a gyro and encoder with a cheap mouse is enticing