adds support for BLE heart rate monitors

2021-04-14 22:13:24 +02:00 · 2021-04-14 22:13:24 +02:00 · 43fa45bf29
parent 870fc53fc8
commit 43fa45bf29
18 changed files with 1466 additions and 337 deletions
--- a/README.md
+++ b/README.md
@ -24,6 +24,7 @@ Open Rowing Monitor implements a physics model to simulate the typical metrics o
 * Strokes per Minute
 * Calories used (kcal)
 * Training Duration
+* Heart Rate (requires BLE Heart Rate Monitor)

 ### Web Interface

--- a/app/ble/CentralManager.js
+++ b/app/ble/CentralManager.js
@ -0,0 +1,158 @@
+'use strict'
+/*
+  Open Rowing Monitor, https://github.com/laberning/openrowingmonitor
+
+  This manager creates a Bluetooth Low Energy (BLE) Central that listens
+  and subscribes to heart rate services
+*/
+import log from 'loglevel'
+import EventEmitter from 'node:events'
+import Noble from '@abandonware/noble/lib/noble.js'
+import NobleBindings from '@abandonware/noble/lib/hci-socket/bindings.js'
+
+// We are using peripherals and centrals at the same time (with bleno and noble).
+// The libraries do not play nice together in this scenario when they see peripherals
+// from each other via the HCI-Socket.
+// This is a quick patch for two handlers in noble that would otherwise throw warnings
+// when they see a peripheral or handle that is managed by bleno
+
+// START of noble patch
+Noble.prototype.onRssiUpdate = function (peripheralUuid, rssi) {
+  const peripheral = this._peripherals[peripheralUuid]
+
+  if (peripheral) {
+    peripheral.rssi = rssi
+    peripheral.emit('rssiUpdate', rssi)
+  }
+}
+
+NobleBindings.prototype.onDisconnComplete = function (handle, reason) {
+  const uuid = this._handles[handle]
+
+  if (uuid) {
+    this._aclStreams[handle].push(null, null)
+    this._gatts[handle].removeAllListeners()
+    this._signalings[handle].removeAllListeners()
+
+    delete this._gatts[uuid]
+    delete this._gatts[handle]
+    delete this._signalings[uuid]
+    delete this._signalings[handle]
+    delete this._aclStreams[handle]
+    delete this._handles[uuid]
+    delete this._handles[handle]
+
+    this.emit('disconnect', uuid)
+  }
+}
+
+const noble = new Noble(new NobleBindings())
+// END of noble patch
+
+function createCentralManager () {
+  const emitter = new EventEmitter()
+  let batteryLevel
+
+  noble.on('stateChange', function (state) {
+    if (state === 'poweredOn') {
+      // search for heart rate service
+      noble.startScanning(['180d'], false)
+    } else {
+      noble.stopScanning()
+    }
+  })
+
+  noble.on('discover', (peripheral) => {
+    noble.stopScanning()
+    connectHeartratePeripheral(peripheral)
+  })
+
+  function connectHeartratePeripheral (peripheral) {
+    // connect to the heart rate sensor
+    peripheral.connect((error) => {
+      if (error) {
+        log.error(error)
+        return
+      }
+      log.info(`heart rate peripheral connected, name: '${peripheral.advertisement?.localName}', id: ${peripheral.id}`)
+      subscribeToHeartrateMeasurement(peripheral)
+    })
+
+    peripheral.once('disconnect', () => {
+      // todo: figure out if we have to dispose the peripheral somehow to prevent memory leaks
+      log.info('heart rate peripheral disconnected, searching new one')
+      batteryLevel = undefined
+      noble.startScanning(['180d'], false)
+    })
+  }
+
+  // see https://www.bluetooth.com/specifications/specs/heart-rate-service-1-0/
+  function subscribeToHeartrateMeasurement (peripheral) {
+    const heartrateMeasurementUUID = '2a37'
+    const batteryLevelUUID = '2a19'
+
+    peripheral.discoverSomeServicesAndCharacteristics([], [heartrateMeasurementUUID, batteryLevelUUID],
+      (error, services, characteristics) => {
+        if (error) {
+          log.error(error)
+          return
+        }
+
+        const heartrateMeasurementCharacteristic = characteristics.find(
+          characteristic => characteristic.uuid === heartrateMeasurementUUID
+        )
+
+        const batteryLevelCharacteristic = characteristics.find(
+          characteristic => characteristic.uuid === batteryLevelUUID
+        )
+
+        if (heartrateMeasurementCharacteristic !== undefined) {
+          heartrateMeasurementCharacteristic.notify(true, (error) => {
+            if (error) {
+              log.error(error)
+              return
+            }
+
+            heartrateMeasurementCharacteristic.on('data', (data, isNotification) => {
+              const buffer = Buffer.from(data)
+              const flags = buffer.readUInt8(0)
+              // bits of the feature flag:
+              // 0: Heart Rate Value Format
+              // 1 + 2: Sensor Contact Status
+              // 3: Energy Expended Status
+              // 4: RR-Interval
+              const heartrateUint16LE = flags & 0b1
+
+              // from the specs:
+              // While most human applications require support for only 255 bpm or less, special
+              // applications (e.g. animals) may require support for higher bpm values.
+              // If the Heart Rate Measurement Value is less than or equal to 255 bpm a UINT8 format
+              // should be used for power savings.
+              // If the Heart Rate Measurement Value exceeds 255 bpm a UINT16 format shall be used.
+              const heartrate = heartrateUint16LE ? buffer.readUInt16LE(1) : buffer.readUInt8(1)
+              emitter.emit('heartrateMeasurement', { heartrate, batteryLevel })
+            })
+          })
+        }
+
+        if (batteryLevelCharacteristic !== undefined) {
+          batteryLevelCharacteristic.notify(true, (error) => {
+            if (error) {
+              log.error(error)
+              return
+            }
+
+            batteryLevelCharacteristic.on('data', (data, isNotification) => {
+              const buffer = Buffer.from(data)
+              batteryLevel = buffer.readUInt8(0)
+            })
+          })
+        }
+      })
+  }
+
+  return Object.assign(emitter, {
+  })
+}
+
+export { createCentralManager }
--- a/app/ble/CentralService.js
+++ b/app/ble/CentralService.js
@ -0,0 +1,20 @@
+'use strict'
+/*
+  Open Rowing Monitor, https://github.com/laberning/openrowingmonitor
+
+  Starts the central manager in a forked thread since noble does not like
+  to run in the same thread as bleno
+  todo: check if noble would also work if we move this into a worker thread
+  (would save some ressources)
+*/
+import { createCentralManager } from './CentralManager.js'
+import process from 'process'
+import config from '../config.js'
+import log from 'loglevel'
+
+log.setLevel(config.loglevel.default)
+const centralManager = createCentralManager()
+
+centralManager.on('heartrateMeasurement', (heartrateMeasurement) => {
+  process.send(heartrateMeasurement)
+})
--- a/app/ble/FtmsPeripheral.js
+++ b/app/ble/FtmsPeripheral.js
@ -98,7 +98,7 @@ function createFtmsPeripheral (controlCallback, options) {

  // present current rowing metrics to FTMS central
  function notifyData (type, data) {
-    if (type === 'strokeFinished' || type === 'rowingPaused') {
+    if (type === 'strokeFinished' || type === 'metricsUpdate') {
      fitnessMachineService.notifyData(data)
    }
  }
--- a/app/ble/ftms/IndoorBikeDataCharacteristic.js
+++ b/app/ble/ftms/IndoorBikeDataCharacteristic.js
@ -83,7 +83,7 @@ export default class IndoorBikeDataCharacteristic extends bleno.Characteristic {
      // Energy per minute
      bufferBuilder.writeUInt8(data.caloriesPerMinute)
      // Heart Rate: Beats per minute with a resolution of 1
-      bufferBuilder.writeUInt8(data.heartRate)
+      bufferBuilder.writeUInt8(data.heartrate)
      // Elapsed Time: Seconds with a resolution of 1
      bufferBuilder.writeUInt16LE(data.durationTotal)

--- a/app/ble/ftms/RowerDataCharacteristic.js
+++ b/app/ble/ftms/RowerDataCharacteristic.js
@ -82,7 +82,7 @@ export default class RowerDataCharacteristic extends bleno.Characteristic {
      // Energy per minute
      bufferBuilder.writeUInt8(data.caloriesPerMinute)
      // Heart Rate: Beats per minute with a resolution of 1
-      bufferBuilder.writeUInt8(data.heartRate)
+      bufferBuilder.writeUInt8(data.heartrate)
      // Elapsed Time: Seconds with a resolution of 1
      bufferBuilder.writeUInt16LE(data.durationTotal)

--- a/app/ble/pm5/Pm5RowingService.js
+++ b/app/ble/pm5/Pm5RowingService.js
@ -76,7 +76,7 @@ export default class PM5RowingService extends bleno.PrimaryService {
  }

  notifyData (type, data) {
-    if (type === 'strokeFinished' || type === 'rowingPaused') {
+    if (type === 'strokeFinished' || type === 'metricsUpdate') {
      this.generalStatus.notify(data)
      this.additionalStatus.notify(data)
      this.additionalStatus2.notify(data)
--- a/app/ble/pm5/characteristic/AdditionalStatus.js
+++ b/app/ble/pm5/characteristic/AdditionalStatus.js
@ -43,8 +43,8 @@ export default class AdditionalStatus extends bleno.Characteristic {
      bufferBuilder.writeUInt16LE(data.speed * 1000 / 3.6)
      // strokeRate: UInt8 in strokes/min
      bufferBuilder.writeUInt8(data.strokesPerMinute)
-      // heartRate: UInt8 in bpm, 255 if invalid
-      bufferBuilder.writeUInt8(255)// data.heartRate
+      // heartrate: UInt8 in bpm, 255 if invalid
+      bufferBuilder.writeUInt8(data.heartrate)
      // currentPace: UInt16LE in 0.01 sec/500m
      // if split is infinite (i.e. while pausing), use the highest possible number
      bufferBuilder.writeUInt16LE(data.split !== Infinity ? data.split * 100 : 0xFFFF)
--- a/app/client/app.js
+++ b/app/client/app.js
@ -7,7 +7,8 @@
 import NoSleep from 'nosleep.js'

 export function createApp () {
-  const fields = ['strokesTotal', 'distanceTotal', 'caloriesTotal', 'power', 'splitFormatted', 'strokesPerMinute', 'durationTotalFormatted', 'peripheralMode']
+  const fields = ['strokesTotal', 'distanceTotal', 'caloriesTotal', 'power', 'heartrate',
+    'splitFormatted', 'strokesPerMinute', 'durationTotalFormatted', 'peripheralMode']
  const fieldFormatter = {
    peripheralMode: (value) => {
      if (value === 'PM5') {
@ -18,7 +19,10 @@ export function createApp () {
        return 'FTMS Rower'
      }
    },
-    distanceTotal: (value) => value >= 10000 ? { value: (value / 1000).toFixed(1), unit: 'km' } : { value, unit: 'm' }
+    distanceTotal:
+    (value) => value >= 10000
+      ? { value: (value / 1000).toFixed(1), unit: 'km' }
+      : { value, unit: 'm' }
  }
  const standalone = (window.location.hash === '#:standalone:')

@ -61,14 +65,31 @@ export function createApp () {
      try {
        const data = JSON.parse(event.data)

+        // show heart rate, if present
+        if (data.heartrate !== undefined) {
+          if (data.heartrate !== 0) {
+            document.getElementById('heartrate-container').style.display = 'inline-block'
+            document.getElementById('strokes-total-container').style.display = 'none'
+          } else {
+            document.getElementById('strokes-total-container').style.display = 'inline-block'
+            document.getElementById('heartrate-container').style.display = 'none'
+          }
+        }
+
+        let activeFields = fields
+        // if we are in reset state only update heart rate and peripheral mode
+        if (data.strokesTotal === 0) {
+          activeFields = ['heartrate', 'peripheralMode']
+        }
+
        for (const [key, value] of Object.entries(data)) {
-          if (fields.includes(key)) {
+          if (activeFields.includes(key)) {
            const valueFormatted = fieldFormatter[key] ? fieldFormatter[key](value) : value
-            if (valueFormatted.value && valueFormatted.unit) {
-              document.getElementById(key).innerHTML = valueFormatted.value
-              document.getElementById(`${key}Unit`).innerHTML = valueFormatted.unit
+            if (valueFormatted.value !== undefined && valueFormatted.unit !== undefined) {
+              if (document.getElementById(key)) document.getElementById(key).innerHTML = valueFormatted.value
+              if (document.getElementById(`${key}Unit`)) document.getElementById(`${key}Unit`).innerHTML = valueFormatted.unit
            } else {
-              document.getElementById(key).innerHTML = valueFormatted
+              if (document.getElementById(key)) document.getElementById(key).innerHTML = valueFormatted
            }
          }
        }
@ -95,8 +116,8 @@ export function createApp () {
  }

  function resetFields () {
-    for (const key of fields) {
-      document.getElementById(key).innerHTML = '--'
+    for (const key of fields.filter((elem) => elem !== 'peripheralMode')) {
+      if (document.getElementById(key)) document.getElementById(key).innerHTML = '--'
    }
  }

--- a/app/client/index.html
+++ b/app/client/index.html
@ -56,30 +56,34 @@
      <span class="metric-unit">/min</span>
    </div>
  </div>
+
  <div class="col">
-    <div class="label">
-      <svg aria-hidden="true" focusable="false" class="icon" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 303.46 303.46">
-        <path fill="currentColor" d="m254.8 278.23-103.07-103.07-103.07 103.07c-18.349 0.91143-22.401-4.2351-21.213-21.213l103.07-103.07-19.755-19.755c-20.183-1.639-63.38-27.119-70.631-34.37l-30.474-30.474c-5.224-5.224-8.101-12.168-8.101-19.555s2.877-14.332 8.102-19.555l18.365-18.365c5.223-5.224 12.167-8.1 19.554-8.1s14.331 2.876 19.554 8.1l30.475 30.475c6.162 6.163 16.762 25.271 22.383 36.609 7.431 14.991 11.352 25.826 11.979 34.014l19.763 19.763 19.762-19.762c0.627-8.188 4.548-19.023 11.98-34.015 5.621-11.34 16.221-30.447 22.383-36.609l30.475-30.475c5.223-5.224 12.167-8.1 19.554-8.1s14.331 2.876 19.554 8.1l18.366 18.366c10.781 10.781 10.782 28.325 1e-3 39.107l-30.476 30.475c-7.25 7.252-50.443 32.731-70.63 34.37l-19.756 19.756 103.07 103.07c-1 17.227-4.2977 21.56-21.214 21.213z"/>
-      </svg>
+    <div id="strokes-total-container">
+      <div class="label">
+        <svg aria-hidden="true" focusable="false" class="icon" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+          <path fill="currentColor" d="m 420.20605,468.95387 33.11371,-33.1137 c 5.22683,-5.22684 8.77492,-17.24658 3.54807,-22.47345 l -2.40714,-2.40718 c -5.22685,-5.22685 -24.05986,3.18856 -30.46144,6.8845 L 208.43041,202.27519 C 197.48359,161.4211 171.36396,110.7189 139.6182,78.964771 L 104.97336,44.31993 C 84.074343,23.420923 78.962098,22.904081 62.197813,39.66838 L 24.014429,77.851751 C 9.0221901,92.843993 7.7868003,99.708469 28.685812,120.60748 l 34.653205,34.65321 c 30.664056,30.66402 82.456343,57.8654 123.310393,68.8122 l 215.56885,215.56886 c -3.69593,6.40155 -12.11135,25.23463 -6.88448,30.46145 l 2.40718,2.40715 c 5.2185,5.21846 17.23824,1.67039 22.46509,-3.55648 z"/>
+          <path fill="currentColor" d="M 93.111861,469.41843 59.998156,436.30471 c -5.226842,-5.22684 -8.774914,-17.24659 -3.548088,-22.47344 l 2.407166,-2.40717 c 5.226836,-5.22685 24.059868,3.18854 30.46142,6.88449 L 304.88751,202.73974 c 10.94682,-40.85409 37.06645,-91.55629 68.81223,-123.310429 L 408.34455,44.78448 c 20.89903,-20.899007 26.01127,-21.415839 42.77554,-4.65156 l 38.18338,38.183384 c 14.99224,14.992241 16.22764,21.856706 -4.67138,42.755726 l -34.65319,34.6532 c -30.66405,30.66404 -82.45634,57.8654 -123.31038,68.8122 L 111.09965,440.10631 c 3.69593,6.40153 12.11135,25.23461 6.88448,30.46143 l -2.40718,2.40716 c -5.21849,5.21846 -17.23824,1.67038 -22.465089,-3.55647 z"/>
+        </svg>
+      </div>
+      <div class="content">
+        <span class="metric-value" id="strokesTotal"></span>
+        <span class="metric-unit">total</span>
+      </div>
    </div>
-    <div class="content">
-      <span class="metric-value" id="strokesTotal"></span>
-      <span class="metric-unit">total</span>
+
+    <div id="heartrate-container">
+      <div class="label">
+        <svg aria-hidden="true" focusable="false" class="icon" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+          <path fill="currentColor" d="M320.2 243.8l-49.7 99.4c-6 12.1-23.4 11.7-28.9-.6l-56.9-126.3-30 71.7H60.6l182.5 186.5c7.1 7.3 18.6 7.3 25.7 0L451.4 288H342.3l-22.1-44.2zM473.7 73.9l-2.4-2.5c-51.5-52.6-135.8-52.6-187.4 0L256 100l-27.9-28.5c-51.5-52.7-135.9-52.7-187.4 0l-2.4 2.4C-10.4 123.7-12.5 203 31 256h102.4l35.9-86.2c5.4-12.9 23.6-13.2 29.4-.4l58.2 129.3 49-97.9c5.9-11.8 22.7-11.8 28.6 0l27.6 55.2H481c43.5-53 41.4-132.3-7.3-182.1z"></path>
+        </svg>
+      </div>
+      <div class="content">
+        <span class="metric-value" id="heartrate"></span>
+        <span class="metric-unit">bpm</span>
+      </div>
    </div>
  </div>
-<!--
-  <div class="col">
-    <div class="label">
-      <svg aria-hidden="true" focusable="false" class="icon" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
-        <path fill="currentColor" d="M320.2 243.8l-49.7 99.4c-6 12.1-23.4 11.7-28.9-.6l-56.9-126.3-30 71.7H60.6l182.5 186.5c7.1 7.3 18.6 7.3 25.7 0L451.4 288H342.3l-22.1-44.2zM473.7 73.9l-2.4-2.5c-51.5-52.6-135.8-52.6-187.4 0L256 100l-27.9-28.5c-51.5-52.7-135.9-52.7-187.4 0l-2.4 2.4C-10.4 123.7-12.5 203 31 256h102.4l35.9-86.2c5.4-12.9 23.6-13.2 29.4-.4l58.2 129.3 49-97.9c5.9-11.8 22.7-11.8 28.6 0l27.6 55.2H481c43.5-53 41.4-132.3-7.3-182.1z"></path>
-      </svg>
-    </div>
-    <div class="content">
-      <span class="metric-value" id="heartRate"></span>
-      <span class="metric-unit">bpm</span>
-    </div>
-  </div>
-->
+
  <div class="col">
    <div class="label">
      <svg aria-hidden="true" focusable="false" class="icon" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><path fill="currentColor" d="M323.56 51.2c-20.8 19.3-39.58 39.59-56.22 59.97C240.08 73.62 206.28 35.53 168 0 69.74 91.17 0 209.96 0 281.6 0 408.85 100.29 512 224 512s224-103.15 224-230.4c0-53.27-51.98-163.14-124.44-230.4zm-19.47 340.65C282.43 407.01 255.72 416 226.86 416 154.71 416 96 368.26 96 290.75c0-38.61 24.31-72.63 72.79-130.75 6.93 7.98 98.83 125.34 98.83 125.34l58.63-66.88c4.14 6.85 7.91 13.55 11.27 19.97 27.35 52.19 15.81 118.97-33.43 153.42z"></path></svg>
--- a/app/client/style.css
+++ b/app/client/style.css
@ -67,7 +67,6 @@ div.label, div.content {

 button {
  outline:none;
-  /* background-color: #00468c; */
  background-color: #365080;
  border: 0;
  color: white;
@ -80,6 +79,10 @@ button {
  width: 3.5em;
 }

-#close-button {
+#close-button, #heartrate-container {
  display:none;
 }
+
+#heartrate-container, #strokes-total-container {
+  width:100%;
+}
--- a/app/engine/MovingIntervalAverager.js
+++ b/app/engine/MovingIntervalAverager.js
@ -23,7 +23,11 @@ function createMovingIntervalAverager (movingDuration) {
  }

  function average () {
-    return sum / duration * movingDuration
+    if (duration > 0) {
+      return sum / duration * movingDuration
+    } else {
+      return 0
+    }
  }

  function reset () {
--- a/app/engine/MovingIntervalAverager.test.js
+++ b/app/engine/MovingIntervalAverager.test.js
@ -8,45 +8,50 @@ import * as assert from 'uvu/assert'
 import { createMovingIntervalAverager } from './MovingIntervalAverager.js'

 test('average of a datapoint with duration of averager is equal to datapoint', () => {
-  const minuteAverager = createMovingIntervalAverager(10)
-  minuteAverager.pushValue(5, 10)
-  assert.is(minuteAverager.average(), 5)
+  const movingAverager = createMovingIntervalAverager(10)
+  movingAverager.pushValue(5, 10)
+  assert.is(movingAverager.average(), 5)
 })

 test('average of a datapoint with half duration of averager is double to datapoint', () => {
-  const minuteAverager = createMovingIntervalAverager(20)
-  minuteAverager.pushValue(5, 10)
-  assert.is(minuteAverager.average(), 10)
+  const movingAverager = createMovingIntervalAverager(20)
+  movingAverager.pushValue(5, 10)
+  assert.is(movingAverager.average(), 10)
 })

 test('average of two identical datapoints with half duration of averager is equal to datapoint sum', () => {
-  const minuteAverager = createMovingIntervalAverager(20)
-  minuteAverager.pushValue(5, 10)
-  minuteAverager.pushValue(5, 10)
-  assert.is(minuteAverager.average(), 10)
+  const movingAverager = createMovingIntervalAverager(20)
+  movingAverager.pushValue(5, 10)
+  movingAverager.pushValue(5, 10)
+  assert.is(movingAverager.average(), 10)
 })

 test('average does not consider datapoints that are outside of duration', () => {
-  const minuteAverager = createMovingIntervalAverager(20)
-  minuteAverager.pushValue(10, 10)
-  minuteAverager.pushValue(5, 10)
-  minuteAverager.pushValue(5, 10)
-  assert.is(minuteAverager.average(), 10)
+  const movingAverager = createMovingIntervalAverager(20)
+  movingAverager.pushValue(10, 10)
+  movingAverager.pushValue(5, 10)
+  movingAverager.pushValue(5, 10)
+  assert.is(movingAverager.average(), 10)
 })

 test('average works with lots of values', () => {
  // one hour
-  const minuteAverager = createMovingIntervalAverager(3000)
+  const movingAverager = createMovingIntervalAverager(3000)
  for (let i = 0; i < 1000; i++) {
-    minuteAverager.pushValue(10, 1)
+    movingAverager.pushValue(10, 1)
  }
  for (let i = 0; i < 1000; i++) {
-    minuteAverager.pushValue(20, 1)
+    movingAverager.pushValue(20, 1)
  }
  for (let i = 0; i < 1000; i++) {
-    minuteAverager.pushValue(30, 2)
+    movingAverager.pushValue(30, 2)
  }
-  assert.is(minuteAverager.average(), 50000)
+  assert.is(movingAverager.average(), 50000)
+})
+
+test('average should return 0 on empty dataset', () => {
+  const movingAverager = createMovingIntervalAverager(10)
+  assert.is(movingAverager.average(), 0)
 })

 test.run()
--- a/app/engine/RowingStatistics.js
+++ b/app/engine/RowingStatistics.js
@ -23,12 +23,26 @@ function createRowingStatistics () {
  let trainingRunning = false
  let durationTimer
  let rowingPausedTimer
+  let heartrateResetTimer
  let distanceTotal = 0.0
  let durationTotal = 0
  let strokesTotal = 0
  let caloriesTotal = 0.0
+  let heartrate = 0
+  let heartrateBatteryLevel = 0
  let lastStrokeDuration = 0.0
  let lastStrokeState = 'RECOVERY'
+  let lastMetrics = {}
+
+  // send metrics to the clients periodically, if the data has changed
+  setInterval(emitMetrics, 1000)
+  function emitMetrics () {
+    const currentMetrics = getMetrics()
+    if (Object.entries(currentMetrics).toString() !== Object.entries(lastMetrics).toString()) {
+      emitter.emit('metricsUpdate', currentMetrics)
+      lastMetrics = currentMetrics
+    }
+  }

  function handleStroke (stroke) {
    if (!trainingRunning) startTraining()
@ -69,6 +83,18 @@ function createRowingStatistics () {
    emitter.emit('strokeStateChanged', getMetrics())
  }

+  // initiated when new heart rate value is received from heart rate sensor
+  function handleHeartrateMeasurement (value) {
+    // set the heart rate to zero, if we did not receive a value for some time
+    if (heartrateResetTimer)clearInterval(heartrateResetTimer)
+    heartrateResetTimer = setTimeout(() => {
+      heartrate = 0
+      heartrateBatteryLevel = 0
+    }, 2000)
+    heartrate = value.heartrate
+    heartrateBatteryLevel = value.batteryLevel
+  }
+
  function getMetrics () {
    const splitTime = speedAverager.weightedAverage() !== 0 ? (500.0 / speedAverager.weightedAverage()) : Infinity
    return {
@ -86,7 +112,9 @@ function createRowingStatistics () {
      powerRatio: powerRatioAverager.weightedAverage().toFixed(2),
      strokesPerMinute: strokeAverager.weightedAverage() !== 0 ? (60.0 / strokeAverager.weightedAverage()).toFixed(1) : 0,
      speed: (speedAverager.weightedAverage() * 3.6).toFixed(2), // km/h
-      strokeState: lastStrokeState
+      strokeState: lastStrokeState,
+      heartrate,
+      heartrateBatteryLevel
    }
  }

@ -115,18 +143,18 @@ function createRowingStatistics () {
    powerRatioAverager.reset()
  }

-  // clear the displayed metrics in case the user pauses rowing
+  // clear the metrics in case the user pauses rowing
  function pauseRowing () {
-    emitter.emit('rowingPaused', getMetrics())
+    strokeAverager.reset()
+    powerAverager.reset()
+    speedAverager.reset()
+    powerRatioAverager.reset()
+    lastStrokeState = 'RECOVERY'
  }

  function startDurationTimer () {
    durationTimer = setInterval(() => {
      durationTotal++
-      emitter.emit('durationUpdate', {
-        durationTotal,
-        durationTotalFormatted: secondsToTimeString(durationTotal)
-      })
    }, 1000)
  }

@ -149,6 +177,7 @@ function createRowingStatistics () {
  return Object.assign(emitter, {
    handleStroke,
    handlePause,
+    handleHeartrateMeasurement,
    handleStrokeStateChanged,
    reset: resetTraining
  })
--- a/app/gpio/GpioTimerService.js
+++ b/app/gpio/GpioTimerService.js
@ -1,6 +1,10 @@
 'use strict'
 /*
  Open Rowing Monitor, https://github.com/laberning/openrowingmonitor
+
+  Measures the time between impulses on the GPIO pin. Started in a
+  separate thread, since we want the measured time to be as close as
+  possible to real time.
 */
 import process from 'process'
 import { Gpio } from 'onoff'
--- a/app/server.js
+++ b/app/server.js
@ -69,62 +69,27 @@ const rowingEngine = createRowingEngine()
 const rowingStatistics = createRowingStatistics()
 rowingEngine.notify(rowingStatistics)

-rowingStatistics.on('strokeFinished', (data) => {
-  log.info(`stroke: ${data.strokesTotal}, dur: ${data.strokeTime}s, power: ${data.power}w` +
-  `, split: ${data.splitFormatted}, ratio: ${data.powerRatio}, dist: ${data.distanceTotal}m` +
-  `, cal: ${data.caloriesTotal}kcal, SPM: ${data.strokesPerMinute}, speed: ${data.speed}km/h` +
-  `, cal/hour: ${data.caloriesPerHour}kcal, cal/minute: ${data.caloriesPerMinute}kcal`)
-  const metrics = {
-    durationTotal: data.durationTotal,
-    durationTotalFormatted: data.durationTotalFormatted,
-    strokesTotal: data.strokesTotal,
-    distanceTotal: data.distanceTotal,
-    caloriesTotal: data.caloriesTotal,
-    caloriesPerMinute: data.caloriesPerMinute,
-    caloriesPerHour: data.caloriesPerHour,
-    power: data.power,
-    splitFormatted: data.splitFormatted,
-    split: data.split,
-    strokesPerMinute: data.strokesPerMinute,
-    speed: data.speed,
-    // todo: no real measurement of heartRate yet
-    heartRate: Math.max(data.caloriesPerMinute * 7, 50),
-    strokeState: data.strokeState
-  }
+rowingStatistics.on('strokeFinished', (metrics) => {
+  log.info(`stroke: ${metrics.strokesTotal}, dur: ${metrics.strokeTime}s, power: ${metrics.power}w` +
+  `, split: ${metrics.splitFormatted}, ratio: ${metrics.powerRatio}, dist: ${metrics.distanceTotal}m` +
+  `, cal: ${metrics.caloriesTotal}kcal, SPM: ${metrics.strokesPerMinute}, speed: ${metrics.speed}km/h` +
+  `, cal/hour: ${metrics.caloriesPerHour}kcal, cal/minute: ${metrics.caloriesPerMinute}kcal`)
  webServer.notifyClients(metrics)
  peripheralManager.notifyMetrics('strokeFinished', metrics)
 })

-rowingStatistics.on('rowingPaused', (data) => {
-  const metrics = {
-    durationTotal: data.durationTotal,
-    durationTotalFormatted: data.durationTotalFormatted,
-    strokesTotal: data.strokesTotal,
-    distanceTotal: data.distanceTotal,
-    caloriesTotal: data.caloriesTotal,
-    caloriesPerMinute: 0,
-    caloriesPerHour: 0,
-    strokesPerMinute: 0,
-    power: 0,
-    splitFormatted: '∞',
-    split: Infinity,
-    speed: 0,
-    // todo: no real measurement of heartRate yet
-    heartRate: Math.max(data.caloriesPerMinute * 7, 50),
-    strokeState: 'RECOVERY'
-  }
-  webServer.notifyClients(metrics)
-  peripheralManager.notifyMetrics('rowingPaused', metrics)
-})
-
 rowingStatistics.on('strokeStateChanged', (metrics) => {
  peripheralManager.notifyMetrics('strokeStateChanged', metrics)
 })

-rowingStatistics.on('durationUpdate', (data) => {
-  webServer.notifyClients({
-    durationTotalFormatted: data.durationTotalFormatted
-  })
+rowingStatistics.on('metricsUpdate', (metrics) => {
+  webServer.notifyClients(metrics)
+  peripheralManager.notifyMetrics('metricsUpdate', metrics)
+})
+
+const bleCentralService = fork('./app/ble/CentralService.js')
+bleCentralService.on('message', (heartrateMeasurement) => {
+  rowingStatistics.handleHeartrateMeasurement(heartrateMeasurement)
 })

 const webServer = createWebServer()
@ -132,10 +97,10 @@ webServer.on('messageReceived', (message) => {
  if (message.command === 'reset') {
    rowingStatistics.reset()
    peripheralManager.notifyStatus({ name: 'reset' })
-  } if (message.command === 'switchPeripheralMode') {
+  } else if (message.command === 'switchPeripheralMode') {
    peripheralManager.switchPeripheralMode()
  } else {
-    log.warn(`invalid command received: ${message}`)
+    log.warn('invalid command received:', message)
  }
 })

--- a/package-lock.json
+++ b/package-lock.json
--- a/package.json
+++ b/package.json
@ -25,24 +25,25 @@
  },
  "dependencies": {
    "@abandonware/bleno": "^0.5.1-3",
+    "@abandonware/noble": "^1.9.2-13",
    "finalhandler": "^1.1.2",
    "http": "0.0.1-security",
    "loglevel": "^1.7.1",
    "nosleep.js": "^0.12.0",
-    "onoff": "^6.0.1",
+    "onoff": "^6.0.2",
    "serve-static": "^1.14.1",
    "ws": "^7.4.4"
  },
  "devDependencies": {
-    "eslint": "^7.23.0",
+    "eslint": "^7.24.0",
    "eslint-config-standard": "^16.0.2",
    "eslint-plugin-import": "^2.22.1",
    "eslint-plugin-node": "^11.1.0",
-    "eslint-plugin-promise": "^4.3.1",
+    "eslint-plugin-promise": "^5.1.0",
    "husky": "^6.0.0",
    "markdownlint-cli": "^0.27.1",
    "npm-run-all": "^4.1.5",
-    "snowpack": "^3.1.2",
+    "snowpack": "^3.3.0",
    "uvu": "^0.5.1",
    "uvu-watch": "^1.0.11"
  }