Linux robots

[markw at mohawksoft.com (markw at mohawksoft.com)]

I'm building a Linux based mobile robot. I started my career as an EE
(wow, 20 years ago!), but now I do mainly software.

I have a Mini-ITX motherboard, wireless network, gellcell battery, LCD
screen, a rudimentary wheeled base (not great, but a starting point),
Veleman 8000 digital/analog I/O system, and a dual H-Bridge MOSFET motor
amplifier.

I'm at the stage where it boots and can move on its own power. It ain't
pretty yet, but hey its fun.

How would you guys do wheel rotation feedback? I need to monitor how much
the wheels move so I can calculate rough position and control velocity. I
have a couple LEDs and photodiodes installed on the wheels that produce a
good set of square waves, not perfectly square, but close to a
"quadrature" encoder. I'm not sure of the resolution yet, but I'll measure
that later.

Do you guys know of a good/cheap/easy updown counter system? I can build,
but would rather buy a kit or something. (I've done my share of
wirewrapping)

Do you think I could hook it up to the printer port and read it fast
enough. (I know that question relies on wheel RPM and resolution, but they
are not too fast and the resolution is fairly slow.)