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HeartRateService

People practicing physical activities use heart rate monitors to track their pulse in real time and improve their physical performances.

The Bluetooth Heart Rate Service defines how data from a heart rate sensor should be exposed through a BLE link. The standard nature of the service allows seamless operations between collectors - usually smartphone applications - and heart rate monitors conforming to the service.

The HeartRateService class implements the Bluetooth Heart Rate service as defined by the Bluetooth body. Makers of BLE enabled fitness devices can use it to expose interoperably heart rate sensor data.

Note: The Bluetooth Heart Rate Service is part of the Bluetooth Heart Rate Profile, which defines behaviors that a Bluetooth heart rate sensor expects. You must ensure that your application conforms to the heart rate profile to guarantee interoperability of your heart rate sensors.

HeartRateService example

/* mbed Microcontroller Library
 * Copyright (c) 2006-2015 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/HeartRateService.h"

DigitalOut led1(LED1, 1);

const static char     DEVICE_NAME[] = "HRM";
static const uint16_t uuid16_list[] = {GattService::UUID_HEART_RATE_SERVICE};

static uint8_t hrmCounter = 100; // init HRM to 100bps
static HeartRateService *hrServicePtr;

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

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

void updateSensorValue() {
    // Do blocking calls or whatever is necessary for sensor polling.
    // In our case, we simply update the HRM measurement.
    hrmCounter++;

    //  100 <= HRM bps <=175
    if (hrmCounter == 175) {
        hrmCounter = 100;
    }

    hrServicePtr->updateHeartRate(hrmCounter);
}

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

    if (BLE::Instance().getGapState().connected) {
        eventQueue.call(updateSensorValue);
    }
}

void onBleInitError(BLE &ble, ble_error_t error)
{
    (void)ble;
    (void)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]);
}

void bleInitComplete(BLE::InitializationCompleteCallbackContext *params)
{
    BLE&        ble   = params->ble;
    ble_error_t error = params->error;

    if (error != BLE_ERROR_NONE) {
        onBleInitError(ble, error);
        return;
    }

    if (ble.getInstanceID() != BLE::DEFAULT_INSTANCE) {
        return;
    }

    ble.gap().onDisconnection(disconnectionCallback);

    /* Setup primary service. */
    hrServicePtr = new HeartRateService(ble, hrmCounter, HeartRateService::LOCATION_FINGER);

    /* 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::GENERIC_HEART_RATE_SENSOR);
    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, periodicCallback);

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

    eventQueue.dispatch_forever();

    return 0;
}

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