Calibrating VDO/Audi speedometer to compensate for

quk@isham-research.freeserve.co.uk quk@isham-research.freeserve.co.uk
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
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