reading automotive Sensors

Using Arduino General Electronics
#1

I'm building a circuit to read the oil pressure sending unit on a 95 jeep wrangler. The sensor is a single wire unit grounded by the engine. It has impedance varying from 1 Ohms (0psi) to 87 (80 psi). 46 ohms = 40 psi.

The vehicles stock gauge has 57 ohms coming from +12v to the sensor and 100 ohm from ground to the sensor. I could use this exact same setup ... feeding 3.3v into a 57 ohm resistor connected to the sensor, connected to a 100 ohm resistor, connected to ground. The 100 ohm resistor is in parallel with the sensor (which seems redundant), so the typical resistance from +3.3V to ground is ~80 Ohms. Thats about 40ma of current which seems to high. Is there any way I can limit the total current through this path without affecting the output voltage reading (much).

#2

Can you make a drawing of that and post it? :o

#3

My circuit diagram.

oil_press_Circuit.png
oil_press_Circuit.png1296×1147 63.2 KB

oil_press_Circuit.png
oil_press_Circuit.png1296×1147 63.2 KB

#4

Are you sure the original gauge was fed by 12V? Most cars built after the 1960s had a 5V regulator for instrument power. I assume you are going to feed the oil pressure signal to the analog input of a 3.3V Arduino or (?).

#5

Yes, the gauges run of 12v. However, I will be running 3.3v through it via a Nano 33 BLE. I'm to the point where I believe a differential opamp circuit is needed for this.

#6