Hi everyone, I have a very stupid question for you.
I'm building a little system and all works well, I'm using arduino for measuring 2 different voltage.
If i measure only one voltage it works fine, but if I connect the 2 GND something happenend and I can't get voltage data.
Let's explain in a better way, I have to read 12V from the input A, and 15V from the input B.
I use 2 different divider, I have connected the input A to the A0 pin, and the GND to the A GND.
I just did the same with B using another pin, connecting the 2 GND, and nothing works.
Any idea? I appreciate a lot any help.
Narsil22:
Hi everyone, I have a very stupid question for you.
I'm building a little system and all works well, I'm using arduino for measuring 2 different voltage.
If i measure only one voltage it works fine, but if I connect the 2 GND something happenend and I can't get voltage data.
Let's explain in a better way, I have to read 12V from the input A, and 15V from the input B.
I use 2 different divider, I have connected the input A to the A0 pin, and the GND to the A GND.
I just did the same with B using another pin, connecting the 2 GND, and nothing works.
Any idea? I appreciate a lot any help.
I assume,
you are measuring the Positive Voltage wire for both the 12 Volt and 15 Volt source?
Correct?
So, the question:
Do you know for a FACT that both Negative Wires, the 12 Volt negative wire and
the 15 Volt negative wire are both at GROUND potential?
No, I really don't know, I thought that I just have to connect them to ground...but I'm missing something...how can I put them to ground?
Where are the voltages coming from?
Yeay, you have to connect both negative pin to GND but only if the power supply is not referenced to the power supply of the Arduino jet. So like a separate wall wart or a battery pack. But if the voltage is some how already connected to the Arduino (or it's power supply) it really depends. There can only be one hard connection (as like to GND) per power supply. So can you draw the whole schematic? (Please no breadboard Fritzing image...)
Voltage come from a solar panel and a battery, all connected by charge controller.
I can get singolar voltage from panel and battery, that's what make me mad.
The only connections between arduino and the two voltage are the wires that I use for make the voltage divider.
I will post the schematic paint soon, thanks you a lot for your help.
Narsil22:
The only connections between arduino and the two voltage are the wires that I use for make the voltage divider.
Uhm, no. Two lines before you said
Narsil22:
all connected by charge controller.
So the ARE already in some way connected. Namely via the charge controller!
And it really depends on the controller you use but it's possible the V+ of the battery and the V+ of the panel are internal connected to each other, NOT the V-'s (aka GND's).... If that's the case, then by connecting both V- to the Arduino GND you just bypass the charge controller and connect the panel direct to the battery....
And yeay, it's not uncommon to place the regulation in the GND path...
You are right! I didn't thought about that! Btw it's worse in this case because now I don't how to fix this!
You have to figure out how the charge controller connects them. Ready datasheets or something.
And what is powering the Arduino?
Arduino is connected via usb to a raspberry pi
And what is powering that?
A raspberry pi power supply with micro-usb, 2A and 5V.
I'm searching the data sheet but I can't found how it connect battery and panel...
Okay, then that's at lest separate.
When the battery and panel are connected (and there is sun... If missed that ball of fire the last couple of days...) you can just connect a multi meter across the V+ terminals. Do the same for the v- terminals. Is the voltage across the V+ terminals 0 (or almost 0)?
I'm not at home this week (I'm studying offsite right now) and I don't have a multi meter here, but I can get it soon. So I will try to read the voltage in the 2 wires.
I've found another thing this afternoon, I have a epsolar LS0512R charge controller, the led of the panel turn green if it's giving some output (if it have sun power to use...), if I connect the 2 dividers with the common ground (the circuit that actually doesn't work) the led turn green even if there is no sun and the panel is not working.
So I assume that the two voltage that I'm going to measure will not me 0...
Okay, no problem.
Narsil22:
if I connect the 2 dividers with the common ground (the circuit that actually doesn't work) the led turn green even if there is no sun and the panel is not working.
Yeay, I still think that by connecting both v- to the same GND you just connect the panel straight to the battery (not good...). But that means the charge controller also sees the battery voltage at the panel input. That would explain the led turning on because you power it from the battery instead of the panel...
Narsil22:
So I assume that the two voltage that I'm going to measure will not me 0...
Not both, one is going to be the difference between the panel and the battery. But I think when you measure across both V+ you'll find 0 (or maybe 1V because of a diode or something) and when you measure across both V- you'll end up with the difference between panel and battery.
IF that's the case a solution would be to go for a common positive system. The positive of the panel and battery are already connected, just add the 5V of the Arduino to it. But then you have to make different voltage dividers and things become a bit more complicated... But it's doable 
OK! Today I'm going to find a voltmeter, in some way, and I will post here results.
By the way...where can I find something about the common positive system that you're talking about?
Today I was finally able to use my multimeter!
As you thought if I measure between the V+ wires I just get 0, while connecting the V- wires I get around 12V!
Should I get some opto-isolator component or I should go for the common positive system you were talking about?