Oli Glaser wrote:
> I haven't been following this thread too well (so ignore this if it's
> already been ruled out for some reason), but from what I have seen I
> can't help thinking something like the "clickety click" detector
> (Ithink) Joe suggested would be the simplest way of doing this,
> hardware and software wise. If you can place a cheap mic (preferably
> with a filter) reasonably near the joins in the track then it should
> be no problem. and pretty accurate - I imagine the mic would not even
> have to be very near as long as it was directional.

This has two main problems:

1 - There will be a great deal of noise on the clicks.  Our human brains ar=
e
very good at extracting such patterns from noise, but electronics or DSP
algorithms may not be so easy or effective.

2 - You still rely on knowing parameters of the train, which in this case i=
s
the spacing between wheels.


It's really amazing how many hairbrain schemes pop up whenever someone asks
a simple question like this.  While this particular one (click detection) i=
s
less so, some have been way far out there without any possibility of useful
or realistic implementations.

The most workable I've heard so far is magnetically sensing passing wheels
at two sensors a short distance from each other.  In this case "short" need=
s
to be somewhat less than the closest distance between two wheels on the
train.  The electonics is simple, there should be little noise on the signa=
l
so that a passing wheel is easy to detect, and it's pretty immune to grease
and grime and dust.


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