wiring the audi a8 speedo sensor

Huw Peplow · 12-09-07, 09:29 AM

The old rf gave a speedo sensor connector and a smiths electronic speedo to work with and so far i have failed to get it working any helpwould be appreciated

the audi sensor creates 4 pulses per revolution picked up via the sensor which is either of the type magnetic or hal/ecu (what does hal mean?) On advice I used the hal terminal but I am uncertain if this is correct as Its probably magnets producing the pulse.

the smiths speedo has eight connections on the rear
1. ignition+ve
2. reset switch (not used)
3.pull up/down if required (what is this?)
4.illumination
5.chasis earth
6.speed pulse input hal/ecu
7.speed pulse input magnetic
8. not used

so far i have used 1,4.5.6, and speedo measures nothing even when coded corectly to 3129 pulses per mile.

I realise that other sensors have been used on the drive shaft but a few people have got theirs to work normally with out addition Noteably Jerry in uk but his memory is a little vague as to exactly the way it works and although I have coppied his instructions its failed

Any idea how to measure the pulsesfrom the sensor, volts etc and as I see it one side sensor is an earth connection the other is the out put to speedo

some electronic genius out there must be able to help

Paul Thompson 'Hooligan' · 12-09-07, 12:55 PM

Hi Huw,

The pickup on the Audi box in Chris's RF has 2-pins and is likely to be magnetic, so pin 7 on speedo would be the appropriate input.

The pull up is a requirement for some situations where either an ECU does not pull the input high or a hall effect sensor does not pull high. I don't think you'll need this as you have a magnetic sensor I believe (2-pin?)..

Bill Hara · 12-09-07, 04:54 PM

Huw
I too have yet to get my speedo working, however I plan on taking it down to Chris the old RF auto elec and designer of the loom to fix this problem in the next week or so. He mentioned to me a couple of weeks ago that he may have figured out the problem b/w the Smiths speedo and the loom interface.
As soon as I get it done I will post the process for you.

Hope this helps... (or you could contact him directly if you like - PM me)

Bill.

Huw Peplow · 12-10-07, 06:48 PM

bill by chance have spoken to audi and the electronic speedo manufacturer today and they say there should be no problems and to check my wiring ,at worst will need a straight ac amplifier to increase the amplitude of the magnetically induced sign wave

Huw Peplow · 12-20-07, 03:34 PM

The problem is solved with the help of paul T.

The audi box sensor is a hal effect item which means that it needs a curent flowing alongthe sensor to speedo which is then modified as a magnet is passed near to its induction coil to create a pulse which then travels to the speedo to be measured.

The sensor has only 2 wires of which one is to earth from where the current is draged through the sensor coils to be modified by the 4 rotating magnets on the drive shafts with in the box.

the speedo has 5 connections one live to run it
one illumination live
one earth to assist the two above functions

The sensor connection
and another live connection to create the potential difference to drag the electrons from earth through the sensor to be pulsed by the near by rotating magnets(the pull up/down wire)

The speedo used by rf is a 200mph replica smiths (with electonic trip) I think they probably had them specially comissioned so probably can supply them .

The new version of this speedo runs directly on connection while there is a previous model with similar connections but needs some switch settings in the rear of its casing

Hope this helps anyone struggling with their speedo