Stack Tacho input S1

[r10crw]

Anyone know what the signal input to the stack is should be? The emerald outputs a pulsed 12V and connecting this into the stack gets it working fine but I found a pull down resistor in the old loom which is maybe needed for longevity??

[robin]

I think you need to preserve that resistor.
The Emerald output is probably an open drain output, i.e. it is driven low by a transistor but is only pulled high by a pull-up resistor. So it can sink a lot of current but source not very much.

The pull down resistor in the loom is then creating a potential divider out of the pull up in the MEMS/Emerald and the resistor in the loom dividing the 12V signal into a 5V signal.

I would leave it in place - it can do no harm ...

Cheers,
Robin

[jimbo]

Ah that reminds me (sorry foe hijacking this) but where is the input for the speedometer located? Is it somewhere behind the rear wheel?
Cheers

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[tut]

Behind the nearside rear wheel.

Sensor fitted by a bolt, fed by a two pin plug.

tut

[robin]

If you have an S2 it's in the same place, but the sensor is integral to the wheel bearing thingmy. Still connected by a two pin plug, though.

Cheers,
Robin

[jimbo]

Cheers, I'll whip off the wheel sometime and have a look

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[r10crw]

I think you need to preserve that resistor.
The Emerald output is probably an open drain output, i.e. it is driven low by a transistor but is only pulled high by a pull-up resistor. So it can sink a lot of current but source not very much.

The pull down resistor in the loom is then creating a potential divider out of the pull up in the MEMS/Emerald and the resistor in the loom dividing the 12V signal into a 5V signal.

I would leave it in place - it can do no harm ...

Cheers,
Robin

Cheers robin,
Yes I think the emrlad has a 1k pull up, just wasn't sure if it was needed as it appeared to be in what was part of the Audi loom. I'll put it in place and if I lose signal I can adjust the value as necessary. Cheers Craig.

[r10crw]

Ps, jimbo as said its near side rear but think its usually in front of the hub.
Craig.
Oh and if it's not working the wire is prone to fracturing just where it goes through the liner as well as plug failure.

[jimbo]

Ok cool, thanks for the info



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