XIAO BLE Sense (nRF52840) Battery Management Library

Overview

This library is designed to manage the battery charging functionality of the XIAO BLE and XIAO BLE Sense board. It supports the following features for a 3.7V LiPo battery:

• Reading battery voltage.
• Calculating battery capacity as a percentage.
• Setting charging modes (fast or slow).
• Registering callbacks for charging state changes.
• Registering callbacks for battery voltage samples.
• One-shot and periodic battery voltage sampling.

The library is built on the Zephyr Real-Time Operating System (RTOS). For comprehensive details on Zephyr and how to get started, visit the Zephyr Getting Started Guide. The Nordic Semiconductor nRF Connect SDK tool with VSCode is a good alternative as it includes Zephyr (and much more).

Features

Battery Voltage Reading

• Function: int battery_get_millivolt(uint16_t *battery_millivolt)
• Description: Calculates the battery voltage using the ADC and stores the value in the provided pointer.
• Usage:

uint16_t voltage;

int ret = battery_get_millivolt(&voltage);
if (ret == 0) {
    // Use the voltage value here
} else {
    // Handle error
}

Battery Percentage Calculation

• Function: int battery_get_percentage(uint8_t *battery_percentage, uint16_t battery_millivolt)
• Description: Calculates the battery percentage based on the voltage and stores it in the provided pointer.
• Usage:

uint8_t percentage;
uint16_t voltage;

battery_get_millivolt(&voltage);

int ret = battery_get_percentage(&percentage, voltage);
if (ret == 0) {
    // Use the percentage value here
} else {
    // Handle error
}

Charging Modes

• Set Fast Charge (Default)

  • Function: int battery_set_fast_charge(void)
  • Description: Sets the battery charging current to fast charge mode (100mA).
  • Usage:

  int ret = battery_set_fast_charge();
  if (ret != 0) {
     // Handle error
  }
  

• Set Slow Charge

  • Function: int battery_set_slow_charge(void)
  • Description: Sets the battery charging current to slow charge mode (50mA).
  • Usage:

  int ret = battery_set_slow_charge();
  if (ret != 0) {
      // Handle error
  }
  

Charging State Change Callback

• Function: int battery_register_charging_changed_callback(battery_charging_changed_callback_t callback)
• Description: Registers a callback function that is executed whenever the charging state changes.
• Callback Type Definition: typedef void (*battery_charging_callback_t)(bool is_charging);
• Usage:

void charging_state_changed(bool is_charging) {
    if (is_charging) {
        // Charging started
    } else {
        // Charging stopped
    }
}

int ret = battery_register_charging_callback(charging_state_changed);
if (ret != 0) {
    // Handle error
}

Battery Sample Ready Callback

• Function: int battery_register_sample_callback(battery_sample_callback_t callback);
• Description: Registers a callback function that is executed whenever a battery voltage sample is ready.
• Callback Type Definition: typedef void (*battery_sample_callback_t)(uint16_t millivolt);
• Usage:

void battery_sample_ready(uint16_t millivolt) {
    // Process the millivolt value
}

int ret = battery_register_sample_callback(battery_sample_ready);
if (ret != 0) {
    // Handle error
}

One-Shot Battery Sampling

• Function: int battery_sample_once(void)
• Description: Initiates a one-time battery voltage sampling. Registered sample callbacks will be called when the sample is ready.
• Usage:

int ret = battery_sample_once();
if (ret != 0) {
    // Handle error
}

Periodic Battery Sampling

• Start Periodic Sampling:

  • Function: int battery_start_sampling(uint32_t interval_ms);
  • Description: Starts periodic sampling of the battery voltage at the specified interval in milliseconds. Registered sample callbacks will be called each time a sample is ready.
  • Usage:

  uint32_t interval_ms = 1000; // Sample every 1 second
  
  int ret = battery_start_sampling(interval_ms);
  if (ret != 0) {
   // Handle error
  }
  

• Stop Periodic Sampling:

  • Function: int battery_stop_sampling(void);
  • Description: Stops periodic sampling of the battery voltage.
  • Usage:

  int ret = battery_stop_sampling();
  if (ret != 0) {
      // Handle error
  }
  

Initialization

• Function: battery_init(void)
• Description: Initializes the battery charging circuit. Must be called before using other battery functions.
• Usage:

int ret = battery_init();
if (ret != 0) {
    // Handle error
}

Example Usage

There is an example in the main.c file that demonstrates how to use the battery management library. This example initializes the battery management library, registers callbacks for charging state changes and battery voltage samples, and starts periodic sampling of the battery voltage.

Programming

Adafruit nRF52 Bootloader

The XIAO BLE Sense is equipped with the Adafruit nRF52 Bootloader, which supports UF2 flashing—a simple drag-and-drop method to program your device.

Entering Bootloader Mode

1. Use a USB-C cable to connect to the XIAO BLE to your computer
2. Double-Click the Reset button (located to the left of the USB connector) quickly. The device should enter bootloader mode and appear as a mass storage device named XIAO on your computer. If the device doesn't appear, ensure your USB cable supports data transfer (some cables are charge-only), and check your computer's device manager or disk utility for new devices.

Flashing the Firmware

• Navigate to the 'build/zephyr/' directory and locate the 'zephyr.uf2' file. If you can not find the build folder, build or rebuild the project.
• Drag and drop the zephyr.uf2 file into the XIAO drive that appeared when the device entered bootloader mode or copy the file using your command line.

After the UF2 file transfer is complete, the XIAO BLE will automatically reset and launch the new application.

For additional information on the flashing process and the XIAO BLE Sense board, refer to the Zephyr Board Documentation for XIAO BLE.

Serial Logging

Connect to the device's serial port to view log messages from the device. Use a serial terminal application (e.g., PuTTY, Tera Term, Minicom) with the following settings:

• Baud Rate: 115200
• Data Bits: 8
• Parity: None
• Stop Bits: 1