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BatteryService

It is often a requirement for devices operating on battery to report the battery charge level to the user.

The Bluetooth Battery Service defines how to expose a battery charge level through a BLE link. It allows a client - usually a smartphone application - of a device to read the current battery charge level and follow its evolution.

The BatteryService class implements the Bluetooth Battery Service as defined by the Bluetooth SIG. Makers of BLE devices operating on battery can use the API to expose interoperably the charge level of their products.

BatteryService class reference

Public Member Functions
 BatteryService (BLE &_ble, uint8_t level=100)
void updateBatteryLevel (uint8_t newLevel)
Protected Attributes
BLEble
uint8_t batteryLevel
ReadOnlyGattCharacteristic< uint8_t > batteryLevelCharacteristic

BatteryService example

/* mbed Microcontroller Library
 * Copyright (c) 2006-2014 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <events/mbed_events.h>
#include <mbed.h>
#include "ble/BLE.h"
#include "ble/Gap.h"
#include "ble/services/BatteryService.h"

DigitalOut led1(LED1, 1);

const static char     DEVICE_NAME[] = "BATTERY";
static const uint16_t uuid16_list[] = {GattService::UUID_BATTERY_SERVICE};

static uint8_t batteryLevel = 50;
static BatteryService* batteryServicePtr;

static EventQueue eventQueue(/* event count */ 16 * EVENTS_EVENT_SIZE);

void disconnectionCallback(const Gap::DisconnectionCallbackParams_t *params)
{
    BLE::Instance().gap().startAdvertising();
}

void updateSensorValue() {
    batteryLevel++;
    if (batteryLevel > 100) {
        batteryLevel = 20;
    }

    batteryServicePtr->updateBatteryLevel(batteryLevel);
}

void blinkCallback(void)
{
    led1 = !led1; /* Do blinky on LED1 while we're waiting for BLE events */

    BLE &ble = BLE::Instance();
    if (ble.gap().getState().connected) {
        eventQueue.call(updateSensorValue);
    }
}

/**
 * This function is called when the ble initialization process has failled
 */
void onBleInitError(BLE &ble, ble_error_t error)
{
    /* Initialization error handling should go here */
}

void printMacAddress()
{
    /* Print out device MAC address to the console*/
    Gap::AddressType_t addr_type;
    Gap::Address_t address;
    BLE::Instance().gap().getAddress(&addr_type, address);
    printf("DEVICE MAC ADDRESS: ");
    for (int i = 5; i >= 1; i--){
        printf("%02x:", address[i]);
    }
    printf("%02x\r\n", address[0]);
}

/**
 * Callback triggered when the ble initialization process has finished
 */
void bleInitComplete(BLE::InitializationCompleteCallbackContext *params)
{
    BLE&        ble   = params->ble;
    ble_error_t error = params->error;

    if (error != BLE_ERROR_NONE) {
        /* In case of error, forward the error handling to onBleInitError */
        onBleInitError(ble, error);
        return;
    }

    /* Ensure that it is the default instance of BLE */
    if(ble.getInstanceID() != BLE::DEFAULT_INSTANCE) {
        return;
    }

    ble.gap().onDisconnection(disconnectionCallback);

    /* Setup primary service */
    batteryServicePtr = new BatteryService(ble, batteryLevel);

    /* Setup advertising */
    ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::BREDR_NOT_SUPPORTED | GapAdvertisingData::LE_GENERAL_DISCOVERABLE);
    ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::COMPLETE_LIST_16BIT_SERVICE_IDS, (uint8_t *) uuid16_list, sizeof(uuid16_list));
    ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::COMPLETE_LOCAL_NAME, (uint8_t *) DEVICE_NAME, sizeof(DEVICE_NAME));
    ble.gap().setAdvertisingType(GapAdvertisingParams::ADV_CONNECTABLE_UNDIRECTED);
    ble.gap().setAdvertisingInterval(1000); /* 1000ms */
    ble.gap().startAdvertising();

    printMacAddress();
}

void scheduleBleEventsProcessing(BLE::OnEventsToProcessCallbackContext* context) {
    BLE &ble = BLE::Instance();
    eventQueue.call(Callback<void()>(&ble, &BLE::processEvents));
}

int main()
{
    eventQueue.call_every(500, blinkCallback);

    BLE &ble = BLE::Instance();
    ble.onEventsToProcess(scheduleBleEventsProcessing);
    ble.init(bleInitComplete);

    eventQueue.dispatch_forever();

    return 0;
}

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