Calibrating VDO/Audi speedometer to compensate for
Wed, 31 Jan 2001 23:00:35+0000

> oh ya, about calibrating the speedo, I don't see anything about adjustment
> in my 5k Bentley. But I think the speedo sensor just outputs a 0-5V signal
> to indicate speed.  So you could adjust this by putting a simple circuit in
> between the sensor and speedo.

Pulses.  It's a Hall sender - the front differential spins a shaft with
a miniscule magnet on top, and the Hall sender sits on top.  On the Type
44, the pulses are actually _counted_ to derive stepping motor pulses
for the odometer - if the rolling radius of the front left wheel is
correct, the system is capable of incredible accuracy.

The digital dash ur-quattros go one stage further - the system is
entirely digital - no analogue values anywhere.  Except in Switzerland,
of course.

Since road speed derived from these pulses is used in so many places,
I'd be cautious about messing with it.

 Phil Payne
 Phone +44 7785 302803   Fax: +44 7785 309674