Date   : Sun, 21 Nov 2010 22:32:45 -0000
From   : mark@... (Mark Usher)
Subject: Using a Beeb for engine monitoring

> > and possibly even black ice warning (however that works).
> 
> I would imagine spectroscopy. Bounce a light (LASER, powerful IR beam?)
> onto the road surface and measure what is reflected, because ice crystals
are
> frequently like a mirror, while a dry road isn't. You'd need to run this
in
> conjunction with a temperature sensor so first Autumn rain on a greasy
road
> doesn't flag up black ice (but, then, maybe the skid risk is similar,
so...?).

As far as I remember they worked on a combination of temperature and
humidity. The ones we put in at Innsbruck airport were serial devices and
not that expensive.

My BMW just gives the outside temp, and when it is below 3 degrees, warns
you to the *possibility* of ice.

Navigation system on the other hand has a gyro motion sensor connected to it
so it can detect when you are turning corners etc, and compensate for the
GPS signal.  For basic needs though, I am sure the GPS calcualtions JGH
mentions would be fine. You could quite easily compare to a SatNav and see
if you need to compensate. 

The MPG swing-o-meter on the dash though is notoriously out by at least 10%.
The actual reading on the on board computer is within about 5% when
comparing to actual litres filled and distance travelled. Car already has an
i2 bus with all the readings floating around on that... hmmm....

//M