Digital Dashboard

Hello guys,

I'm working on a digital dashboard using seven segment displays and a 20x4 character display. I'm curious about interfacing with sensors in my truck though. For instance, my fuel sending unit outputs around 20ohms when full and 200 ohms when empty. How would I interface this with the arduino to measure resistance?

Thanks,
Sam

The more important thing is what voltage is it using as Arduino can only accept a max of 5V DC

Here's some information about the fuel sender from my service manual:

A constant current
source of about 32 mA is supplied to the resistor
track on the fuel gauge sending unit. This is fed
directly from the Powertrain Control Module (PCM).
The resistor track is used to vary the voltage depending
on fuel tank float level. As fuel level increases,
the float and arm move up, which decreases voltage.
As fuel level decreases, the float and arm move
down, which increases voltage. The varied voltage
signal is returned back to the PCM through the sensor
return circuit. Output voltages will vary from
about .6 volts at FULL, to about 8.6 volts at EMPTY
(Jeep models), or, about 7.0 volts at EMPTY (Dodge
Truck models).

(I drive a dodge truck)

The fuel gauge sending unit contains a variable
resistor (track). As the float moves up or down, electrical
resistance will change. Refer to 8, Instrument
Panel and Gauges for Fuel Gauge testing. To test the
gauge sending unit only, it must be removed from
vehicle. The unit is part of the fuel pump module.
Refer to Fuel Pump Module Removal/Installation for
procedures. Measure the resistance across the sending
unit terminals. With float in up position, resistance
should be 20 ohms ±6 ohms. With float in
down position, resistance should be 220 ohms ±6
ohms.

That's all I know about it.

Output voltages will vary from
about .6 volts at FULL, to about 8.6 volts at EMPTY
(Jeep models), or, about 7.0 volts at EMPTY (Dodge
Truck models).

Your going to need a voltage divider to make the voltage level safe for your arduino as anything over 5 could/will damage your arduino pin. Ideally you should confirm the max voltage the sender supplies and pick resistor values to give a larger voltage range or just use a 50/50 split (same resistor both sides) to half the voltage. This means full will be about 0.3V and empty on your Dodge about 3.5V. This is about 655 steps on the Arduino ADC and even with losing lower 4 bits to noise that's still 63 steps

Alright, so will a couple of usual metal film resistors do the trick? Sounds easy.