Race Technology

Hi,

we have the problem to connect an Audi OEM fuel sensor (potentiometer) with the Dash2.

The OEM sensor has only 2 pins, one for the ground and the other one to connect to dashboard.

How does it fit?

With voltmeter, I can measure a resistance between these two pins, according to the amount of fuel.

But it doesn`t work fitting one of the pins to DL1 5V output and the other one to analogue input.

Where is my wrong thinking ?

Thanks a lot !

I think the problem is that from what you describe, the fuel sender isn't a potentiometer but a rheostat, i.e. it outputs a resistance reading rather than a voltage.

You need to modify the wiring to allow it to act as a potentiometer - just like RT themselves do with some of there own senders.

What you are doing is creating a resistor divider, (or voltage divider), the wiring will be as per RT's instructions for three wire sensors, BUT the value of the fixed resistance WILL PROBABLY be different.

The +5v ref output from the logger will go to one leg of a fixed value resistor, the other leg of the resistor will connect to the output of the fuel sender, this output will also connect to the analogue input on the logger. The other sender connection - the ground, connects to ground on the logger.

Before you can determine the value of the fixed resistor, you're going to need to accurately measure the range of resistances of the sender., in order to plug them into the equation.

Have a read here to find out more, including details of the calculation.

http://en.wikipedia.org/wiki/Potential_divider

Thanks a lot for your help!
I am going to try this out, giving a feedback after testing.

Perfect, it´s working as described !

Dave,

Thanks, this also worked 100% on my Ford Fiesta.

Gary...
GMS Racing - South Africa

Found a handy calculator on one of the sites linked to from the wikipedia article http://www.sengpielaudio.com/calculator ... ivider.htm

Thanks Dave!

RTUSA wrote:Found a handy calculator on one of the sites linked to from the wikipedia article http://www.sengpielaudio.com/calculator ... ivider.htm

Thanks Dave!

Yep, found that myself - after doing the calculations manually, still it was nice to double check the math.

I've been using the stock VDO sensor/Dash 2 on the road for about a month now in this configuration, and it's worked really well. In fact, thanks to the software filtering/damping options on the input, it actually works much better than the original analogue VDO gauge. (The readings used to fluctuate wildly below half a tank).

Hi
I'm trying to do this but only using the Dash 2. Can anyone tell me how it would work as there is no reference voltage from the unit?

I guess you've got two choices, provide a regulated power supply somehow, or try and get hold of a rheostat type fuel level sender. I seem to remember a thread on Blatchat while I was researching how to do this. IIRC they'd found a source of three wire rheostat type senders. Might be worth a search.

A general Google on "5 volt voltage regulator" throws up a number of sample circuits, with bits you could get from Maplins fairly cheaply; doesn't look too difficult to copy one, (famous last words). But then I'm no electronics expert.

Cidersurfer:

Contact Race Technology in Nottingham, we are making up some external 5V regulators that should help.

Out of interest what sort of damping / smoothing / filtering is done on the raw voltage coming from the fuel sensor ? My sensor (same as Mk4 fiesta) outputs between 3.5 (full) and 7 (empty) volts with fluctuations up to around 2 volts when on track.

What happens if you have 2 senders?

Do you do the same but connect the ground from the last sender back

Cheers Adam