BluetoothLE-HeartRate

bluetoothle-heartrate is a Node.js package that listens for heart rate data from a Polar H7 Bluetooth Low Energy (BLE) heart rate sensor (using noble, a popular Node.js library for connecting to BLE devices), formats the data as JSON or InfluxDB's Line Protocol, and writes it to /dev/stdout.

index.js is loosely derived from @jakelear/node-h7-hr but is now pretty much a rewrite. I split up functions where it seemed logical, improved error/bounds-checking, and added lots more commentary.

Instructions

• Clone this repo: git clone https://github.com/chbrown/BluetoothLE-HeartRate
• Attach the Polar H7 to its strap and put it on.
• Ensure no other applications or devices are connected (listening) to the Polar H7.
• Run npm install, then node server.js (or npm start, which relies on the default npm script to do the same thing).

Alternatively, the main function in server.js checks for a --json argument, so run node server.js --json to get (line-delimited) JSON output.

This library was developed for the Polar H7 specifically, but should work with other BLE devices that use the service 180d and the characteristic 2a37 (see the references for links to the official Bluetooth specifications for these identifiers).

Debugging

On macOS, you can run system_profiler SPBluetoothDataType to list the currently paired/configured Bluetooth devices. For example, while the node server.js process is running, that command outputs this on my machine:

Bluetooth:

      Apple Bluetooth Software Version: 5.0.5f1
      [...]
      Devices (Paired, Configured, etc.):
          [...]
          Polar H7 2A61B41A:
              Address: 00-22-D0-2A-61-B4
              Random Address: No
              Services:
              Paired: No
              Configured: No
              Connected: Yes
              Class of Device: Low Energy
              AFH: On
              AFH Map: ffffffff1f
              RSSI: -53
              Role: Central
              Connection Mode: Active Mode
              Interval: 0 ms
          [...]

Resources and references

• Introduction to Core Bluetooth: Building a Heart Rate Monitor: http://www.raywenderlich.com/52080/introduction-core-bluetooth-building-heart-rate-monitor
  • 2013 article using Objective-C and iOS's CoreBluetooth to build (in Xcode 5) an iPhone app (on iOS 7) to monitor heart rate.
• Apple Developer - Guides and Sample Code: CoreBluetooth Heart Rate Monitor: https://developer.apple.com/library/content/samplecode/HeartRateMonitor/Introduction/Intro.html
  • 2011 sample app demonstrating using Objective-C to monitor heart rate on Mac OS X 10.7.2 Lion or later
• noble npm package
• Service 0x180D ("Heart Rate"): https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.service.heart_rate.xml
• Characteristic 0x2A37 ("Heart Rate Measurement"): https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.heart_rate_measurement.xml

License

Copyright 2018 Christopher Brown. MIT Licensed.