I have made a throttle position indicator using the throttle position sensor that was existing in the car for the EFI system. Its output is around 0.5 volts at closed throttle and 4.5 volts at full throttle.

I used an Arduino Nano, and a buck converter set at 8 volts to feed the Nano, power to the buck converter is from the car battery which has an output of about 13.5 volts. I have used an OLED display to display the throttle position with the command,

int percent = map (throttlePosition, 85, 920, 0, 100);

I connected the earth from the throttle sensor to the Arduino and the signal wire which runs back to the ECU to pin A0 of the Nano. The current into the A0 pin is 10mA. The vehicle is a 1988 Range Rover Classic.

With the ignition on but the engine off the correct reading is shown on the display as you press the throttle. When the engine is running the display just shows random shapes and figures, pressing the throttle has no effect on the display.

How do I make it so the system works while the engine is running? I am not sure why it’s doing what it is doing, or how to fix it.

 

Can you post the circuit you used?
What filtering do you have on the power supply and the sensor signal?

 

I will have to draw up the circuit layout.
I have used no filtering.

 

Try something like this.
The 100nF capacitor may be enough, but if it still plays up, add a 1uF Tantalum as well.
The diodes are for transient protection and my not be needed but it is better to add them.
Keep your leads short, and do not use a breadboard with long jumper wires. A car is a pretty electrically noisy place.

 

Can I use a 100nF electrolytic capacitor. If I do need a tantalum capacitor, does it go in parallel with the 100nF?

 

The 100nF (or 0.1uF) is a ceramic or poly cap. and, yes, the electro or tant is in parallel with it. The idea is to smooth the signal from the sensor to get rid of the noise. The response time does not need to be fast.

 

I tried a ceramic 0.1uf in parallel with a 1uf tantalum. It has got rid of most of the random image on the display.
The display now shows a number but when I press the throttle the number doesn't change, nothing on the display changes.
As before, all ok with the motor off.
Will have to add the diodes and see.

 

I tried a ceramic 0.1uf in parallel with a 1uf tantalum. It has got rid of most of the random image on the display.
The display now shows a number but when I press the throttle the number doesn't change, nothing on the display changes.
As before, all ok with the motor off.
Will have to add the diodes and see.

Don’t forget to draw up the circuit.

 

This is the circuit, how I originally made it with no filters.

 

OK, I see one major problem and also now I see that there is a display that uses an OLED. It does not matter to me one bit the type of display, that statement confused the issue. "Digital Display" would have been clear and adequate.
Is the wiring between the variable resistor and the circuit assembly shielded? An engine compartment is full of high energy electrical noise. In addition,where is the voltage source for the TPS??? A resistance type sensor requires a source voltage

 

There is a separate 5v input to the TPS which shares the same ground as the ground wire I am using from the TPS.

 

There is a separate 5v input to the TPS which shares the same ground as the ground wire I am using from the TPS.

OK, I did not see it on the drawing, and my mind-reading ability is rather poor, especially at a distance..
It does seem that the problem is noise related.