Monitor battery charge in hid keyboard example

[bscdb]

The hid keyboard example includes the battery service. But how does it work? I would like to monitor the battery charge. After I use the voltage divider, to which AIN pin should I connect? Where will the battery charge be displayed?

[Jørgen Holmefjord]

Did you enable notifications for the battery service? The timer that triggers SAADC sampling is not started until the BLE_BAS_EVT_NOTIFICATION_ENABLED event is received in on_bas_evt().

[bscdb]

Hi Jorgen,

The code worked when I tried to increase the range from 0V - 5V.

What are these hex values 06, 01, ...

I think I should modify the below function

static __INLINE uint8_t battery_level_in_percent(const uint16_t mvolts)
{
    uint8_t battery_level;

    if (mvolts >= 3000)
    {
        battery_level = 100;
    }
    else if (mvolts > 2900)
    {
        battery_level = 100 - ((3000 - mvolts) * 58) / 100;
    }
    else if (mvolts > 2740)
    {
        battery_level = 42 - ((2900 - mvolts) * 24) / 160;
    }
    else if (mvolts > 2440)
    {
        battery_level = 18 - ((2740 - mvolts) * 12) / 300;
    }
    else if (mvolts > 2100)
    {
        battery_level = 6 - ((2440 - mvolts) * 6) / 340;
    }
    else
    {
        battery_level = 0;
    }

    return battery_level;
}

Can you tell me how are the calculations made?

[Jørgen Holmefjord]

The function will return a battery percentage from a given input voltage. This is a intended to represent a typical discharge curve for a CR2032 battery. You need to modify the calculations to match your board and battery. You mention that you use voltage divider/potentiometer. Are you sure that the input to the pin after this voltage regulation is high enough to be above 2.1 V?

[bscdb]

Yes the voltage goes above 2.1V. I think thats why I notice some changes in hex values. But dont you think they are pretty low? I mean of course I have to modify the above function but stil.

[Jørgen Holmefjord]

If you are seeing changing battery percentage and the measured voltage is not high above 2.1 V, it should be correct. You need to measure what you get in and modify the formula to fit your needs.