I have a project where I want to measure voltages (0-5V) with Arduino Uno R3.
However, when I put A0..A2 to breadboard and measure against ground (one analog input at a time) all the 3 values change together. HOWEVER. If i measure from A2, it only affects the reading of A2.
I am measuring a battery and also just putting my fingers to the wires.
I use LabView and Labview interface for arduino (LIFA) so that I can see all the voltages at once easily.
Question is: How to protect the three Analog Inputs from each other?
I think i should put diodes and caps somewhere. I tried to put a cap between Aref and GND. Then i tried to put a cap between A0 and ground, and measure the voltage in parallel against that cap. Didn't solve my problem.
EDIT: Also i would like to add.. that this setup will measure voltage when I put my hand close to the wires (I see a rising voltage). I don't even need to touch them.
EDIT2: Guys I think I solved this one. If I use for example 1K/1K Voltage Divider, my problem disappears! 1:1 divider would give me 1/2 of the actual voltage and it suppresses the "returning currents" or whatever is the correct term..
You are seeing the effects of trying to measure a analog input pin while it has a 'floating input pin" condition. It is not valid to utilize any reading you take of a analog input pin that has nothing wired to it. You will just see the results of electrical noise (such as you hand/finger close to the pin) and capacitance coupling between the pins having no valid electrical inputs wired to them.
So time to move on with your projects. There is nothing unusual about what you are seeing and should have no effect on any real use you have for the analog input pins.
retrolefty:
You are seeing the effects of trying to measure a analog input pin while it has a 'floating input pin" condition. It is not valid to utilize any reading you take of a analog input pin that has nothing wired to it. You will just see the results of electrical noise (such as you hand/finger close to the pin) and capacitance coupling between the pins having no valid electrical inputs wired to them.
So time to move on with your projects. There is nothing unusual about what you are seeing and should have no effect on any real use you have for the analog input pins.
Lefty
Yes, thanks. I used this experiment of unconnected wires to build a Theremin for myself (with help of a PC speaker).
I see lots of these "measure voltage with your Arduino" howto's but I didn't find any explanation how would I get around this problem
In my application, I have a "mechanical testbench" that connects the wires to my product that I want to measure. So it is very important the wires get connected properly and that is also the reason why I can't trust they are always automatically connected.
