Rheostat, Shift Range of Values by -100 Ohm (Car Fuel Level)

Other Hardware General Electronics
1

Quick question about Rheostat, resistors ect.

Car project I am working on and have swapped the dash cluster. Problem is the Rheostat in the fuel tank works on two different ranges depending on if the vehicle is flex fuel or not.

I have a flex fuel sender in my fuel tank. It operates on a Range of 100-500 Ohm. Full is 100 Ohm, Empty is 500 Ohm.

The non Flex Fuel senders operate on a range of 0-400 Ohm, Full is 0 Ohm while Empty is 400 Ohm.

Problem is my new cluster is from a non flex vehicle. So my gauge in the dash is operating on the 0-400 Ohm range while my sender in the tank is operating on 100-500 Ohm. This means the needle on the gauge is off by 1/4 tank. When my tank is full the sender is saying 100 Ohm, but for the gauge is showing 3/4 Tank because for it 0 Ohm is full.

So is there anyway to negatively shift the range of the rheostat by 100 Ohms. If the problem was reversed it would be easy to add a 100 Ohm resistor in series creating a positive shift upward.

I am not sure if it is possible to remove 100 ohms from a DC circuit. Any thoughts?

Can the arduino read in these signals, modify them and send out a new adjusted one?

I read about adding a resistor in parallel but that cuts the entire range say in half. I need a linear shift downward across the entire range.

Only other options are to drop the fuel tank and change the sending unit or source another gauge cluster with the right gauge. Both of which would be very expensive.

Any options or input here? Thanks

2

Yes, but you will probably need to change the voltage levels that you read and send out

3

If the current isn't too high you could use a digital potentiometer driven by an Arduino.

Or if the gauge is an old-style meter movement (or if it's "voltage driven") you can drive it directly with PWM (you might need a transistor or MOSFET driver depending on the resistance of the gauge). Put a voltage divider on an analog input and map() the input/output values.

You can easily shift a voltage with an op-amp summing amplifier or a differential (subtraction) amplifier.