Attopilot current and volt sensor problem

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What steps will reproduce the problem?
1.  Connect 180A or 90A attopilot sensor as per Option 2 instructions from wiki
2.  APM 2.5 board, 4S 5000mah batter
3.  ESC voltage measured at 5.04.  Entered voltage in MP as 5.01

What is the expected output? What do you see instead?
16.V expected, 0A expected
4.  MP reports pack voltage as 13.5V or thereabouts, Amps 254

What version of the product are you using? On what operating system?
Arduplane 2.65, Windows 7, MP 1.2.20

Please provide any additional information below.

Original issue reported on code.google.com by wild....@gmail.com on 21 Nov 2012 at 3:42

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You should measure voltage on the out pins A0 -A11 eg. Then your value for 
adding to MP should be arround 4.74V (-0.3). But the valuses must still be 
"tuned" for me

Original comment by Gregm...@gmail.com on 24 Nov 2012 at 8:06

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Hi,
Yeas as Gregm wrote you need to measure your ESC volts minus 0.3 voltage drop 
in a diode. And enter a measured batt voltage followed (!) by TAB key. You 
should then see the calculated divider value change, and the calculated voltage 
change too. If not, try again, it is not really reliable from MP.
To the the ampere meter to read zero, you need to go to the advanced parameter 
list(!) and find AMP_OFFSET. There you enter the voltage at the ammeter sensor 
output when the current is zero. This should get the reading near zero, with 
the remainder owing to inaccuracy in APMs voltage measurement wrt. that of your 
voltmeter. Eleminate the remainder by trial and error increments and decrements 
of AMP_OFFSET.
Regards Soren

Original comment by Soren.Kuula@gmail.com on 15 Dec 2012 at 12:23