Not a simple project, but it goes to show what can be created with old computer parts that most people toss in the garbage.

“The basic principle of Three Blind Mice is to run three threads round three rollers from old mechanical mice. By using the mouse reports to calculate the length of the extended thread this allows the position where all the threads join to be calculated. First job was to interface the mice to a PC. I am using old Microsoft Itellimice. The “z” axis on these mice which measures the position of the wheel is very low resolution and not suitable for this application. So, you need two mice to get the three axis of measurement required.

It turns out that Windows makes it rather hard to extract input from individual mice if you have several connected to your PC. It is also rather tricky to override the normal mouse behaviour of moving the Windows cursor. Therefore rather than connect the mice directly to a PC I decided to interface the mice to an AVR microcontroller. The AVR then has a serial interface to the host PC.

The PS/2 mouse interface is a bit of pain to work with, but with a bit of effort I was able to get things connected.”