readme and comments

index.js

@@ -2,24 +2,37 @@ var noble = require('noble');
 
 noble.on('stateChange', function(state) {
   if (state === 'poweredOn') {
+    // Seek for peripherals broadcasting the heart rate service
+    // This will pick up a Polar H7 and should pick up other ble heart rate bands
+    // Will use whichever the first one discovered is if more than one are in range
     noble.startScanning(["180d"]);
   } else {
     noble.stopScanning();
   }
 });
 
 noble.on('discover', function(peripheral) {
+  // Once peripheral is discovered, stop scanning
   noble.stopScanning();
+
+  // connect to the heart rate sensor
   peripheral.connect(function(error){
     // 180d is the bluetooth service for heart rate:
     // https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.heart_rate.xml
     var serviceUUID = ["180d"];
     // 2a37 is the characteristic for heart rate measurement
+    // https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml
     var characteristicUUID = ["2a37"];
 
+    // use noble's discoverSomeServicesAndCharacteristics
+    // scoped to the heart rate service and measurement characteristic
     peripheral.discoverSomeServicesAndCharacteristics(serviceUUID, characteristicUUID, function(error, services, characteristics){
       characteristics[0].notify(true, function(error){
         characteristics[0].on('data', function(data, isNotification){
+          // Upon receiving data, output the BPM
+          // The actual BPM data is stored in the 2nd bit in data (at array index 1)
+          // Thanks Steve Daniel: http://www.raywenderlich.com/52080/introduction-core-bluetooth-building-heart-rate-monitor
+          // Measurement docs here: https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml
           console.log('data is: ' + data[1]);
         });
       });

readme.md

@@ -0,0 +1,18 @@
+# Log heart rate from a Polar H7 using node
+
+A rudamentary example of using [Noble](https://github.com/sandeepmistry/noble) to listen to heart rate data from a Polar H7 bluetooth heart rate sensor.
+
+`index.js` is pretty short and thoroughly commented. The code is pretty naive, it just finds the first bluetooth peripheral transmitting the bluetooth heart rate service and listens for the measurement data.
+
+## How to use this
+
+- [Install node](https://nodejs.org/en/download/)
+- Clone this repo
+- In the root directory, run `npm install` to install noble
+- While wearing the Polar H7, run `node index.js`
+- After a few seconds, you should see heart rate data logged into the terminal
+
+## Notes
+This _should_ function with other bluetooth heart rate sensors that broadcast the 180d service.
+This does not include Fitbit Charge HR - to my knowledge the Charge HR does not broadcast the
+heart rate service over bluetooth.