6 Replies Latest reply on Mar 21, 2016 2:11 AM by llynch Branched from an earlier discussion. Branched to a new discussion.

    Measuring Battery life with BCM2073XS (Con't)

      Per this thread here: Measuring Battery life with BCM20732S


      I am in a very similar boat to the original poster.


      I have a battery that can vary in voltage from 2.8 to 4.2v.

      For this reason I have a 2.8v (output) regulator connected between my battery and the VBAT pin of my bcm20737s.


      When I turn on my module and view the battery percentage, it is always roughly 66%.


      What I intend on adding to the next revision if my board is the following circuit:


      Supply is connected to my battery (2.8 to 4.2v)

      BATT is connected to P8 (ADC)

      BATT control is connected to P24 (GPIO)


      As my bcm20737s is running at 2.8v passing straight in my battery voltage to P8 would be very harmful as it is above the recommended input voltage. Also it would be larger then my adc voltage reference.


      So I have set up a voltage divider law (2K2 & 1K1) which when my battery is at 4.2v, P8 will see 2.8v.

      As there is a voltage divider according, and I left my module sitting on a shelf for a long time my battery would eventually run dead.


      So I have included a npn transistor. The transistor is controlling the ground path of the voltage divider.

      If I apply voltage to the base of the transistor my voltage divider will be connected to ground and the flow of electricity can occur.

      if I do not apply voltage on the base of my transistor my voltage divider will not be connected to ground and the flow of electricity cannot occur.


      This same theory can be applied to improve power consumption while the module is running.


      I know I will have to pass the voltage of P8 to the function that is calculating the battery voltage currently.

      I also know I will have to change a few parameters for the calculation to be correct.


      Can anyone see any problem with the above design?

      How will I pass the voltage of P8 to the current battery calculator?