Trying to get Heart Rate Variability from Polar H10 [Bluetooth Low Energy Sample UWP]

Question

I am working with Polar H10 to get the Heart Rate Variability from it.

I am running Bluetooth Low Energy Sample from Microsoft.

I have used this sample to get the heart rates from another polar device (Polar OH1) and it worked fine.

But now I want to get the HRV from Polar H10. But BLE sample code is not really showing me the HRV Characteristic which it should just like heart rate.

These are the only characteristics I am seeing:

 // first layer keys are serviceUuid's
// second layer keys are characteristicUuid's
// with their respective name/description as values
{
    "1800"    /* Generic Access */                      : {
    "2a00": "Device Name",
    "2a01": "Appearance",
    "2a02": "Peripheral Privacy Flag",
    "2a03": "Reconnection Address",
    "2a04": "Peripheral Preferred Connection Parameters"
},
"1801"    /* Generic Attribute */                   : {
    "2a05": "Service Changed"
},
"180d"    /* Heart Rate */                          : {
    "2a37": "Heart Rate Measurement",
    "2a38": "Body Sensor Location"
   // This is where it should show Heart Rate Variability //
},
"180a"    /* Device Information */                  : {
    "2a23": "System ID",
    "2a24": "Model Number String",
    "2a25": "Serial Number String",
    "2a26": "Firmware Revision String",
    "2a27": "Hardware Revision String",
    "2a28": "Software Revision String",
    "2a29": "Manufacturer Name String"
},
"180f"    /* Battery Service */                     : {
    "2a19": "Battery Level"
},
"6217ff4b-fb31-1140-ad5a-a45545d7ecf3" /* unknown */: {
    "6217ff4c-c8ec-b1fb-1380-3ad986708e2d": "unknown", /* read:true */ // value = 
     uInt16Array [3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    "6217ff4d-91bb-91d0-7e2a-7cd3bda8a1f3": "unknown" /* write:true, 
     indicate:true, descriptors:{ descriptorUuid: "2902" }*/
 {
     /* 6172 */
     this service has all the numbers which I have no idea about. 
     Example: 10905, 10906, and etc.  
  }
}

Does anyone know what adjustments should I make to the code so that I can get HRV?

                 **EDIT::** 


           private static ushort ParseHeartRateValue(byte[] data)
    {

        // Heart Rate profile defined flag values
        const byte heartRateValueFormat = 0x01;

        byte flags = data[0];
        bool isHeartRateValueSizeLong = ((flags & heartRateValueFormat) != 0);

        if (isHeartRateValueSizeLong)
        {
            return BitConverter.ToUInt16(data, 1);
        }
        else
        {
            return data[1];
        }
    }

////AFTER UPDATING ABOVE METHOD//////

          private static ushort ParseHeartRateValue(byte[] data)
    {
        ushort offset = 1;
        // Heart Rate profile defined flag values
        const byte heartRateValueFormat = 0x01;

        byte flags = data[0];
        bool rr = (flags & (1 << 4)) != 0;
        if (rr)
        {
            int count = (data.Length - offset) / 2;
            for (int i = 0; i < count; i++)
            {

                ushort value = BitConverter.ToUInt16(data, offset);

                double intervalLengthInSeconds = value / 1024.0;
                offset += 2;
            }
        }
        bool isHeartRateValueSizeLong = ((flags & heartRateValueFormat) != 0);

        if (isHeartRateValueSizeLong)
        {
            return BitConverter.ToUInt16(data, 1);
        }
        else 
        {
            return data[1];
        }

    }

Answer 1

The device you use follow the Heart Rate Bluetooth specification. So the data it sends should respect this standard. if you refer to this documentation , you will read the 0x2A37 characteristic, which you listed in your question, but you should not receive it as an int.

The different values given by the characteristic are listed in the documentation I linked. I think that you will be interested by the 'RR-Interval', which is given with a resolution of 1/1024 second.

You will need to retrieve the required bytes from your value. Be careful about the byte order. As the documentation states:

The fields in the above table are in the order of LSO to MSO. Where LSO = Least Significant Octet and MSO = Most Significant Octet.

So you are looking for the last 2 bytes of the value, since the RR-Interval is an uint16.