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Li-Polymer with i2c chip

Discussion in 'Microcontrollers, Programming and IoT' started by john2k, Jul 1, 2015.

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  1. john2k


    Jun 13, 2012
    I have a Google Nexus tablet which has a 3.8V Li-Polymer. I want to remove the battery completely and run the tablet directly on a step down converter running at 3.8V. I've tested the theory and the tablet works fine. Only problem is that the Li-Polymer battery of the tablet has 2 additional wires which I am told provide temperature and charge state data via a i2c controller chip so that the tablet knows what percentage the battery is at and what temperature it is so that it can go into thermal shutdown if needed.

    Because I have left out those 2 data wires, the tablet is constantly showing 0% battery and as a result of this certain things are restricted by the tablet. I found a post by a user where he sniffed the i2c data and find out what the Nexus asked for and then wrote a code running on an Arduino to give the tablet fixed information, e.g. battery is at 100% and temperature is 19 degrees.

    I'm wondering if there is any kind of i2c emulators that anyone knows of where I can set certain permanent parameters to send back via those 2 data lines to the tablet. Or is there any other way to fool the tablet into thinking it has full charge and that temperature is at certain value?

    Many thanks
  2. ver chan

    ver chan

    Jun 27, 2015
    why do you need to remove the batteries and powered it using converter? your gadget might be damaged if you make some mistakes on it.
  3. john2k


    Jun 13, 2012
    Because I am installing the device as a car multimedia display and in very hot sunny weather the temperature of the battery gets very hot without use and the tablet goes into thermal shutdown. Not to mention the risk of battery explosion. Quite a few people have therefore completely removed battery and used a properly regulated 3.75v power supply that constantly feeds the tablet and the tablet is put into deep sleep through ignition relay. This all works fine for me however the problem I face is send fake data back that usually the battery i2c chip sends back to the tablet
  4. brevor


    Apr 9, 2013
    You could try to carefully take apart the battery and remove the temp/voltage sensing circuit and reconnect it into your power supply to read the voltage. If the temp. sensor is a separate part you may be able to replace it with a resistor.
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