The PC mice use a slotted wheel and a pair of photo sensors for each of 
the 2 directions of travel. Everything is relative motion (fore/back) 
and speed. The limits of the screen are determined in software, I think 
sometimes actually in the video card. Instead of a set of pots, probably 
a pair digital pots might work. This is all I know from recent issues 
with a PC mouse port where the mouse is supplied 5VDC, ground, a clock 
from the motherboard, and a data return line. Try googling for PC mouse 
circuit or something like that.

bob wrote:
> I need to control a mouse pointer with two potentiometers. No buttons needed. I have tried to adapt the USB firmware from Microsoft using the 16c745 but my experience and understanding of this is limited. If I use two of the ADC channels for the pots, can I control the pointer this way? How about substituting a 16F818 or 916 (or anything I can reprogram ) for the 16c? I would like to use a usb connection for this. Any suggestions? Assembly language would be best for me
>                                                                                                         Thanks
>                                                                                                         BobL
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