Fuel gauge help

[Adam37tr]

Right got all connected up , tested resistance across sensors before connected and got 55ohms, jacked the up car to see any fluctuation and did see a change ie went down to 51ohms before adding 1k resistor.

Ive put a 1k resistor across and connected upto lite monitor, shows around 0.014v ish

tried jacking car up to see any change but does not change or very little
would this mean I dont need the resistor in?

Cheers Adam

[osborni]

I'm getting the feeling that you might not know what a pull up resistor does...



The fuel tank sender represents the "sensor". The 1k resistor is in the diagram.

55 ohms is about right for a fuel sender gauge. I think you will need a 500Ohm resistor to have enough voltage swing. A 1K will only give you about a 1 volt swing from an empty tank to a full tank. 500Ohm will give you about a 1.6-2 volt swing. Depends on how accurate you need to be. If you are measuring to 1/10ths of a tank, it should be fine. But if you want to measure fuel consumption, it might not have enough resolution.

Calculator: http://www.electronics2000.co.uk/calc/p ... ulator.php

The problem with a lower Ohm resistor is that you will draw more current from your DL1. You will need to add up how many sensors you have and what they draw to figure that out.

Ohm's law: V=IR to figure out the current draw on a pull up resistor network.

Simplest solution is to use a $5 linear voltage regulator from Radio Shack with $5 in other misc parts.

The other solution for better resolution is to use a 10 volt regulator to boost the voltage going to the sensor. (12 VDC is too close to the 13.8 VDC that most cars run at - it will not be a stable voltage signal.) That will give you more volts out and a higher resolution.

[Adam37tr]

Cheers for that , will try the 500ohm resistor

Ive only got 2 other sensors oil press and oil temp from race tech
the rest are off ecu

Think my biggest prob will be getting readings for a calc as dont use car much

Cheers Adam

[Adam37tr]

Right ive measured it full and get about 4ohms and around 55ohms with a quarter of a tank

Just gota try it with empty tank

[osborni]

I'm guessing either a VDO or a GM sender.....

[Peter Carroll/Toronto]

Don't wire them in parallel or you will get strange results. If one of the senders goes to 0 ohms (short), then the parallel reading will also be zero regardless of how much fuel is on the other side of the tank.

[Adam37tr]

They are wired in series as from manufacturer spec and pic on 1st page

Still not got much further with it though, think it reads about 2.15v full tank , need more time at it

Any more info appreciated though

[Peter Carroll/Toronto]

We had problems wiring dual senders in parallel. If one goes to zero, then the parallel resistance also becomes zero. This will give you impossible readings in high G corners. Wiring the senders in series resolves the problem. We use a 1K resistor with good results on BMWs.

Rc = (R1 + R2) /2

except when R1 or R2 = 0!