It seems to me that an optical mouse would make a good basis for an "MPG".  One could mount the mouse electronics in a little housing, looking at the surface of a disc rotated by the jog wheel.  The easiest approach would be to cannibalise an off the shelf mouse rather than try to use the bare sensing chip.  However most of the mice you get these days have a USB input and this is handled on the chip itself so you would have to interface using USB.  Has anyone interfaced a mouse to Mach, does anyone know please?

John.

Hi, John, this may be of some interest to you-

http://www.cnczone.com/forums/general_electronics_discussion/51494-cheap_mpg_cnc_using_optical.html

Dave

Thanks.