On Mon, 24 Nov 1997 22:43:28 -0800 john blackburn <johnb@dircon.co.uk>
writes:
>
>a near-infinite life. Headlamp bulbs don't last long, and dynamos give
>particular problems due to poor voltage regulation. If you pedal fast
>they blow. You can buy 2 zener diodes in a plastic case to connect
>across the dynamo to "clip" the peaks. It costs $10! Sometimes the
>(100mW) zener diodes also blow, because these bicycle folks aren't
>very
>smart.

I think a bridge rectifier, then a "super zener" made of a low-wattage
zener from the collector to base of a power transistor would do this job.
 Shouldn't cost very much.  The shunt regulator is probably best since
most simple series regulator designs would lose some voltage at low
speeds.


>The "PIC related" bit (I'm really sorry about all this...)
>My folding bicycle has 16-inch wheels. I bought a cheap cycle computer
>but I find it can only be calibrated for 20, 22, 24, 26 and 27 inch
>wheels. Can I use a PIC-chip to adapt this computer to my bicycle?

A 16-inch wheel should make 3 revolutions to cover the same ground that a
24-inch one does in two.  So a circuit to discard every third pulse from
the sensor but pass the other two on to the computer could be used.  Then
set the computer up for a 24 inch wheel.  If the thickness of the tires
makes the result not exact, add or drop a pulse every once in a while so
as to remove long-term error.

This kind of logic could be easily done with a PIC.  Maybe put the PIC to
sleep after every pulse and use the RB or GPIO wakeup to wake up.  Of
course just a RC oscillator would do, and keep count in RAM.