How do I measure battery level on an Nrf51422 without external components?

[TFred]

I have a custom PCB with an nrf51422 powered by a coin cell battery. The EE who designed the board assured me that the battery voltage could be measured internally through the ADC. That EE is now tied up and cannot help.

What is the proper method for measuring this voltage? It is a standard feature in nearly all devices, yet the inclusion of a resistor set will leak current. Any direction would be appreciated. Thanks.

Edit: I am able to find examples of battery service updates, but these updates are based on a simulated battery as per the code below. I have not yet found an example of configuring of the ADC to VCC.

static void battery_level_update(void)
{
    uint32_t err_code;
    uint8_t  battery_level;

    battery_level = (uint8_t)sensorsim_measure(&m_battery_sim_state, &m_battery_sim_cfg);

    err_code = ble_bas_battery_level_update(&m_bas, battery_level);
    if ((err_code != NRF_SUCCESS) &&
        (err_code != NRF_ERROR_INVALID_STATE) &&
        (err_code != BLE_ERROR_NO_TX_BUFFERS) &&
        (err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING)
        )
    {
        APP_ERROR_HANDLER(err_code);
    }
}

[Nguyen Hoan Hoang]

There is no addition hardware require. You need to use the ADC and configure it to sense the VCC. This all done pragmatically. There are example code in the SDK. I don't recall which one. Browse through all the examples, you'll find it.

[Nguyen Hoan Hoang]

look at the adc_simple example in peripheral folder.

[Mohamed O.Abouzeid]

can I use the ADC to sense the battery & to wake up the system on the same application ? ?

[Nguyen Hoan Hoang]

sure there are 8 add channels and about 30 i/o you can use. I have applications that 3 adc at the same time, other 20 i/o at the same time.

[Mohamed O.Abouzeid]

I found how to use the adc to measure the vcc but I face some problems, when I finish I'll put the code in an answer comment thanks for your great advice