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### Topic: measure battery voltage (Read 1 time)previous topic - next topic

#### GekoCH

##### Mar 07, 2011, 10:04 pm
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

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

#### retrolefty

#1
##### Mar 07, 2011, 10:06 pm
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

#### GekoCH

#2
##### Mar 07, 2011, 10:13 pm
Hope this helps...

#### Grumpy_Mike

#3
##### Mar 07, 2011, 10:13 pm
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.

#### GekoCH

#4
##### Mar 07, 2011, 10:23 pmLast Edit: Mar 07, 2011, 10:26 pm by GekoCH Reason: 1

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?)

#### Grumpy_Mike

#5
##### Mar 07, 2011, 11:15 pm
Put a capacitor across R2 to remove noise.

#### retrolefty

#6
##### Mar 07, 2011, 11:22 pm
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

#### Grumpy_Mike

#7
##### Mar 07, 2011, 11:33 pm
Quote
can you use a ohm better

Theirs no place like ohm.

#### retrolefty

#8
##### Mar 07, 2011, 11:41 pm

Quote
can you use a ohm better

Theirs no place like ohm.

My spell checker is as dumb as dirt.

#### GekoCH

#9
##### Mar 08, 2011, 07:11 am

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?

#### Grumpy_Mike

#10
##### Mar 08, 2011, 10:43 am
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.

#### BenF

#11
##### Mar 08, 2011, 11:50 am
Is this a standard Arduino (Uno, Duemilanove) or something you built?

Two measurements that would eliminate a lot of speculation are as follows:

- Voltage between Arduino Aref and Arduino Gnd
- Voltage between Battery + and Arduino Gnd

If you post these measurements, I'm sure you'll get some useful answers.

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