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### Topic: reading automotive Sensors (Read 373 times)previous topic - next topic

#### Levine1978

##### Nov 03, 2019, 03:11 am
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).

#### JCA34F

#1
##### Nov 03, 2019, 05:37 am
Can you make a drawing of that and post it?
https://forum.arduino.cc/index.php?topic=519037.0

#### Levine1978

#2
##### Nov 03, 2019, 11:05 amLast Edit: Nov 03, 2019, 11:10 am by Levine1978
My circuit diagram.

#### JCA34F

#3
##### Nov 04, 2019, 06:20 amLast Edit: Nov 04, 2019, 06:21 am by JCA34F
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 (?).

#### Levine1978

#4
##### Nov 04, 2019, 11:25 am
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.

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