Wind Vane's potentiometer values change depending on power source

Other Hardware Sensors
1

I have a Davis Anemometer that I'd like to connect to my arduino uno weather station.

I used the guide stated here: Davis Anemometer Arduino Hookup | Code (Part 1 of 3)

When I tested the wind vane at the bench, the values that came from the pot seemed in line with what the guide stated.
However, on my weather station I have a power bus that feeds all of the components, as well the the MCU.
It can be powered from the USB on the arduino, or the solar panel/battery or whatever.

When I power the Wind Vane from the bus, the pot values are way off, and seem to taper from 0 - 1024.

I imagine that it has something to do with a different resistance in the bus as opposed to right from the arduino 5V pin.

How do I proceed?

Edit: After some testing. Even having the bus ground plugged into the arduino, and running the wind vane directly from the Arduino 5V/Gnd, tends to send the wind vane's values way out of wack.

Edit: It's the I2C bus that's connected to the power bus. Isolating the I2C bus, causes the wind vane to display the correct values.

Edit: Plugging any I2C device into the I2C bus,(which takes it's 5v/GND from the power bus mentioned above) and then connecting the SCLK and SDA lines, causes the issue.

As soon as I unplug the data and clock lines, the wind vanes values switch back to normal.

Edit: Do I need to maybe connect a lead from the 5V power bus to the AREF?

Fritzing attached

Weather_bb.jpg
Weather_bb.jpg2415×1527 430 KB

2

A4 and A5 are used for I2C.

The example uses analogue input A4 for wind direction.
Did you change that to a different input.
Leo..

3

I am using the dedicated SCLK and SDA pins on the arduino R3.
But this could certainly be a clue.

I was not aware of the fact that A4 and A5 had some relation to I2C.
When it stops raining, I'll switch the pins and give it a shot.

4

You were right Leo,
Moving the wind sensor to A0 instead of A4 or A5 worked.

I guess I never figured that the SDA and SCK pins were wired in parellel to the Analogs.

Thanks much.