Hy
At the moment I'm running an Arduino with an 1S LiPo (3.7V) with an
5v Step-Up regulator. Now I like to monitor also the lipo voltage with
an Analoge input. But when I do connected the battery to an Analog
Input it always reads ~5V.
How can I get the real value of around 4V?
I know this question has alredy been asked in the old forum but the solution didn't worked...
Thx
Andy
That doesn't sound right at all. Could you post a drawing showing how you have wired the batter/dc-dc convertor/arduino power and analog input pin/ and all the gound connections ?
I'm pretty sure you must have something wired incorrectly. What you wish to do should be straight forward.
Lefty
Hope this helps...
It is possible that the step up regulator is generating noise that is giving you a false reading. Try and have a potential divider across the battery and measure across the bottom resistor. Also put some capacitance across the input, to try and reduce the noise.
R1=56k
R2=15k
Battery is 4.1V
Arduino gives me back: 1.94V this would mean =7.24V?????
(If I calculated right the Arduino should read 0.866V or am I wrong?)
Put a capacitor across R2 to remove noise.
Do you have a link to that DC/DC converter? I'm wondering if it could be an isolated converter (no ground continuity from input to outout) ? If not, can you use a ohm better and see if the negitive in and out pins show continuity?
The first way you showed it wired up should work if it's not a isolated converter. Not sure about it being a noise issue or not, only a scope would verify that or not.
Lefty
can you use a ohm better
Theirs no place like ohm.
Grumpy_Mike:
can you use a ohm better
Theirs no place like ohm.
My spell checker is as dumb as dirt. 
retrolefty:
Do you have a link to that DC/DC converter? I'm wondering if it could be an isolated converter (no ground continuity from input to outout) ? If not, can you use a ohm better and see if the negitive in and out pins show continuity?The first way you showed it wired up should work if it's not a isolated converter. Not sure about it being a noise issue or not, only a scope would verify that or not.
Lefty
The converter is this one.
http://www.bodhilabs.com/vpackbareaaa.html
Do you know a better one?
What lefty means is try and connect the battery -ve directly to the arduino -ve, not "through" the board.
Sorry the link is not much help, we need to see a schematic.
Is this a standard Arduino (Uno, Duemilanove) or something you built?
Two measurements that would eliminate a lot of speculation are as follows:
If you post these measurements, I'm sure you'll get some useful answers.