I put together a speedometer re-calibrator for my Suzuki motorcycle 
using a 12F683 with a 20 Mhz resonator. Works well, and most of the code 
came from www.piclist.com (24 bit add, 256 filter, 24 bit countdown, 
etc...) Other parts were sparked from discussions on this list. Thanks!
The circuit uses the GP2 rising edge int and TMR1 to measure the 
incoming pulse, stretches it by a percentage, and sets TMR0 counting 
down to the output. The desired percent change (from 0% to ~25%) is set 
by reading a 25 turn pot (~1% per turn) and using the ADRESH 8 bit value 
for a loop count on a routine that adds the incoming period with 1/1024 
of the incoming period. (256/1024 = ~25%). Source code / pictures are at 
http://ca.geocities.com/sniderj@rogers.com/SV1K_speedo/sv_speedo.html . 
Prototype was built using a "Device on Device" technique, with epoxy 
poured on it, and then heatshrink.
As the unit is mounted down by the engine (and may be heated quite a 
bit), does the ceramic resonator merely go off frequency with excessive 
heat - or will it stop completely?  As the pot heats up, will the ouput 
voltage change - or because both sides of the resistance tap are seeing 
the same heat will it  not change? Is there anything else that could be 
changed to make it more robust?
TIA;
John Snider

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