> > The most complex part about this is going to be the detection of RPM.
> >
> > One option is to use a reed switch mounted near the spokes and a
> > magnet mounted on the spoke itself.
> 
> A reed switch is not a good choice.  This is usually done with a permanent
> magnet between two spokes of the back wheel as far radially outward as
> possible and a pickup coil on the frame.  A little analog electronics and
> you get a pulse into the PIC once per wheel rotation.


You'd better let the bike industry know, everyone uses reed switches.  

And everyone puts them on the front wheel.  

Of course 'everyone' means 'nearly everyone' as no doubt there's a few
oddball solutions that are more expensive and don't work any better than a
reed switch that you just might be able to buy.  Maybe someone still makes
the old mechanical type.

You can buy them for $5 off eBay anyway.  Clock, odometer, trip distance &
time, current, max & average speed, RPM, wheel size etc.  

Pricier units (but not by much) give you wireless (meaning another batter to
change), the ability to use the one meter on different bikes, RS232 and
other fairly useless stuff.

Get a GPS instead.  That'll give you slope.

Tony



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