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APM 2.5 Voltage Sensing

Posted by Etienne on September 26, 2012 at 12:11pm

Hi all,

If I'm only interested in checking the level of my main batteries, do I really need the voltage and current sensor?  Or is it possible to use a resistor to bring down the voltage to below 5V and then calibrate via parameters to get the correct reading (as one could do in APM1)?

Will a 3200 ohm resistor be good enough for a 11.1V (3s) LiPo pack?

It takes weeks for any order to arrive here in South-Africa and it would be cool if I could at least check the battery pack voltage level in the mean time.

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Replies

  • fpvwannabe March 2, 2013 at 4:05pm

    all,

    i cannot make any sense of this. i am trying to calibrate apm for my voltage sensor (a simple 3:1 voltage divider). with a 3s battery outputting 11.76v, i am measuring 2.76v from my voltage divider (the ratio with my chosen resustors were not exactly 3:1). i would have expected MP to ask me for these two voltages: 11.76v and 2.76v so as to be able to calculated actual voltage from the divided voltage available on the signal pin of a1.

    but instead, MP asks for "measured battery voltage" (this make sense to me, i enter 11.76 here) and APM input voltage which, as i read the docs, is the voltage provided by to power the apm. this voltage is just south of 5v in my case and obviously independent of the pack voltage as its outputted by a voltage regulator. i do not understand why i have to enter this value and i do not understand where i should enter 2.76v

    can someone shed some light on this? is apm trying to save me work by measuring this value itself from the a1 signal pin? this would be a problem for me as i power the whole apm from a1. i have jp1 disconnected, and using a1 to provide ground, regulated 5v and the divided voltage (2.76v here) for the apm. i have to have the usb connected while setting apm up, so cannot have a1 connected at the same time.

    any feedback is appreciated. thanks.

  • Captain Silver February 17, 2013 at 4:23pm

    i can´t see these "Volt Dividers"  pins on APM 2.5 board.

    can anybody help me - thanks

    ralf

  • Patch Thompson November 11, 2012 at 4:10pm

    Will apm 2.5 support multiple voltage monitoring with the sparkfun v-breakout? I.E. Main, Video, Avionics etc?

  • Justin September 28, 2012 at 3:32pm

    According to http://code.google.com/p/ardupilot-mega/wiki/Voltage you'll need to use the voltage and current sensor https://www.sparkfun.com/products/9028 ... Well at least for APM 2.0, it doesn't have any information on APM 2.5 which I've recently received so I'm in the same boat.

    Can someone confirm the connections are the same for APM 2.5 to connect the sensor?

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