Fuel sender 3 ohm to 110 ohm change to 5-0V

[trav.jzx]

Hoping someone can help me, I need to convert 3 - 110 ohm range to 5V - 0V range.

I built the device from this thread:

Fuel sender 0-5v help

Hi guys, I use a megasquirt ECU permanantly hooked up to a linux system with touchscreen. I'm in the process of binning the dials completely and using just the screen. I'm slightly stuck at the fuel gauge stage. The ECU has a spare input which accepts 0-5v. It also has a 5v reference...

www.electro-tech-online.com

Unfortunately this shows full when the tank is empty and empty when the tank is full as it works in the opposite direction.

Also I noticed that its not the safest to components as without any resistance from the fuel sender it outputs 10V.

Thanks.

 

[Pommie]

Can you wire your device such that the 0-5Vis the ground connection? I.E. a 5v meter will see 0V when the output is 5V as both terminals will have 5V on them.

Mike.

 

[alec_t]

You could follow U1 with a unity-gain inverting opamp stage. If U1 ia a dual opamp you already have the two stages you need. A zener diode could clamp the output to, say, 4.7V.

 

[Nigel Goodwin]

You could follow U1 with a unity-gain inverting opamp stage.

Or just wire U1 in inverting mode?

 

[trav.jzx]

I am unable to wire it as the ground connection unfortunately as the gauge us apart of the cluster and therefore shares the ground with other gauges.

Unfortunately I am not super clued up on electronic components only the basics, I am an auto electrician though. I can follow a schematic but unable to draw one myself. Cheers

 

[dougy83]

You can just wire it up as inverting; see attached. Single rail opamp like the LM358 should be alright. The little kink towards the right of the graph is because the opamp is not a rail-to-rail type, but I doubt it matters for your use case

 

[trav.jzx]

Thanks for that! I will give it a go, it should also stop it from outputting higher than 5V now too under certain circumstances do you think?

 

[dougy83]

You're welcome. It will output 0V if the variable resistor is disconnected. The 2k2 (R7) should limit the output current if the output voltage exceeds 5V, which it doesn't by much, as you can see from the graph, when the resistance is 0 ohms (or if the sensor input goes to a negative voltage due to noise or bad grounding). If you're worried, use a rail-to-rail opamp powered from 5V. Also a capacitor between the sensor input and ground will reduce noise somewhat.

 

[trav.jzx]

Too easy, I will try as is and see how it performs. Thanks again!