I need a solution for a car application. I'd like to take the fuel level sensor resistance and split it into 2 outputs, one different (based on a ratio or certain parameters in relation to the original reading), and the second one the same.
IN - from Fuel Level Sender 4-85ohm (4ohm full, 85 empty, 35 half tank)
OUT1 - to PCM connector 40-250ohm (40ohm full, 250ohm empty)
OUT2 - to Fuel Gauge 4-50ohm (same as IN)
The fuel level sender is analog, just a float on a 20" piece of resistive material that moves up and down.
Someone gave me a heads up and mentioned using an arduino controller with a digital 1kohm 4ch pot. he mentioned using all 4 channels to get a 1ohm resolution, which would be great.
The problem with using digipots in this application is that they have quite low current limits. The pot you linked to is rated at 5mA continuous, whereas the 4-85 ohm one might have carry around 1A.
As one side of the fuel sender is grounded, and the device it is connected to is presumably a simple analog meter connected to (probably) +5v, you could simulate the 4-85 ohm sender using a mosfet. See attached schematic. Adjust the PWM so that the reading on pin A1 divided by the reading on A2 is the desired resistance (higher PWM = lower effecting resistance).
For simulating the 40-250 ohm sender, whether a similar solution will work depends on the input circuitry of the PCM computer. If it's a resistor to +5V feeding a ADC, then a similar solution would work, but use a 10 ohm resistor instead of 1 ohm.
i was thinking about the current as well. I'm pretty sure the gauge works via +12V (in which case i'll need a voltage divider?) but i will check voltage and current draw sometime this weekend.
I don't have an understanding of how mosfets works, so i'll have to do some research to understand your schematic.
I'm pretty sure the PCM uses +5v for signal, i will check that too. why would i use a 10K ohm resistor instead of a 1k ohm?
