>and the 24 bit version should actually be:
>
>0x1000000 * 1 / 2.367 = 0x6C275E
>

Thanks for this Josef, Jim and Sergio, looks like the way to go, no
messy dividing numbers on a small pic, just adding, and quick response
to speed change too which might help when the cruise control gets hold
of the signal and tries to use it ( a possible downside of your original
"time it and resynthesise" suggestion Jim ).

Now to sort out the signal conditioning side for input and output... I'm
hoping the speedo won't mind a pulse train rather than the sine wave it
normally gets. First job is to just generate a suitable frequency and
feed it in (voltage divided down a bit) to see what happens.

I'll keep you all posted.

Cheers,
     Robin.




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