Alan asks:

> Well I was assuning you would use a PIC for the data collection. However I
can
> now see why you would want to do it the way you propose. I would also guess
that
> it is a case of not needing to make it absolutely micro miniature as it
could be
> connected to a car battery in 99.9999% of cases, at least for recharging
most of
> the time. from this I would take it that you could happily use the PIC with
the
> largest RAM etc.

That's right.  It's a small hand-held box that plugs into the car's cigarette
lighter to recharge the battery.  We use a 17C44 with 64K of external RAM.
Once you've set up the macros/subroutines for talking to the external RAM it's
no problem at all.

> Just how accurate does the FFT need to be? I do not have expertise in this
area,
> but if it was to show as a "bargraph" on a graphics LCD (spectrum analyser
> style) does this save you anything? I assume that the good/bad decision
would be
> made by someone looking at the picture to decide if the "out of band"
> resonance's/artefacts are sufficient to condemn the pole.

Highly accurate, unfortunately.  It does not show the spectrum to the user.
Instead a complicated algorithm is run on the spectrum which weights certain
frequency bands, applies a statistical function to the weighted spectrum, and
extracts from that a good/bad indication which is given to the user on a
simple text display.  I'm not allowed to give details about that bit because
it's the subject of a patent application and my employer would have my balls
for a bowtie!!

Steve Thackery
Suffolk, England.
Web Site: http://www.btinternet.com/~stevethack/