read

Access a characteristic on your peripheral device and read its data.

Create a connection to a nearby Bluetooth Low Energy peripheral device.

b = ble("Thingy")

b = 
  ble with properties:

               Name: "Thingy"
            Address: "F2DF635320F6"
          Connected: 1
           Services: [9×2 table]
    Characteristics: [38×5 table]

Show services and characteristics

Create a characteristic object that represents the "Temperature" characteristic.

c = characteristic(b,"Weather Station Service","Temperature")

c = 
  Characteristic with properties:

             Name: "Temperature"
             UUID: "EF680201-9B35-4933-9B10-52FFA9740042"
       Attributes: "Notify"
      Descriptors: [1x3 table]
 DataAvailableFcn: []

Show descriptors

Because this characteristic supports "Notify", you can use read to get the latest data.

data = read(c)

data = 1×2

    23    75

You can also return the timestamp of the latest data.

[data,timestamp] = read(c)

data = 1×2

    23    73

timestamp = datetime
   16-May-2019 16:20:00

Interpret the data in Celsius. The first byte represents the integer part of the temperature and the second byte represents the decimal part with a resolution of 0.01.

temperature = data(1) + data(2)*0.01

temperature = 23.7300

Access a characteristic on your peripheral device and create a callback function to read its data.

Create a connection to a nearby Bluetooth Low Energy peripheral device.

b = ble("Thingy")

b = 
  ble with properties:

               Name: "Thingy"
            Address: "F2DF635320F6"
          Connected: 1
           Services: [9×2 table]
    Characteristics: [38×5 table]

Show services and characteristics

Create a characteristic object that represents the "Temperature" characteristic.

c = characteristic(b,"Weather Station Service","Temperature")

c = 
  Characteristic with properties:

             Name: "Temperature"
             UUID: "EF680201-9B35-4933-9B10-52FFA9740042"
       Attributes: "Notify"
      Descriptors: [1x3 table]
 DataAvailableFcn: []

Show descriptors

Because this characteristic supports "Notify", you can create a callback function. Name the function displayCharacteristicData and define it as follows. Specify the read mode as 'oldest' instead of 'latest'. Calling the 'latest' data may lead to errors in the callback function caused by the flushing of previous data.

function displayCharacteristicData(src,evt)
    [data,timestamp] = read(src,'oldest');
    disp(data);
    disp(timestamp);
end

Use the @ operator to assign the function handle to the DataAvailableFcn property of the characteristic. When a new notification is available, the data appears in your command window.

c.DataAvailableFcn = @displayCharacteristicData

c = 
  Characteristic with properties:

             Name: "Temperature"
             UUID: "EF680201-9B35-4933-9B10-52FFA9740042"
       Attributes: "Notify"
      Descriptors: [1x3 table]
 DataAvailableFcn: displayCharacteristicData

Show descriptors

After you finish working with the characteristic, disable notifications using unsubscribe.

unsubscribe(c)

Access a descriptor on your peripheral device and read its data.

Create a connection to a nearby Bluetooth Low Energy peripheral device.

b = ble("DemoDev")

b = 
  ble with properties:

               Name: "DemoDev"
            Address: "FF548EA5658F"
          Connected: 1
           Services: [5×2 table]
    Characteristics: [10×5 table]

Show services and characteristics

Create a characteristic object that represents the "Heart Rate Measurement" characteristic.

c = characteristic(b,"Heart Rate","Heart Rate Measurement")

c = 
  Characteristic with properties:

             Name: "Heart Rate Measurement"
             UUID: "2A37"
       Attributes: "Notify"
      Descriptors: [1x3 table]
 DataAvailableFcn: []

Show descriptors

Create a descriptor object that represents the "Client Characteristic Configuration" descriptor.

d = descriptor(c,"Client Characteristic Configuration")

d = 
  Descriptor with properties:

          Name: "Client Characteristic Configuration"
          UUID: "2902"
    Attributes: ["Read"    "Write"]

This descriptor contains information about whether notification and indication are enabled or disabled. You can use read to get the current data.

data = read(d)

data = 1×2

     0     0

Interpret this data by referring to the specification for this descriptor found in the Bluetooth Core Specification on the Bluetooth SIG website.

This value changes when the notification or indication status changes. For example, subscribe to notification using subscribe. Then, observe the change in the value by reading the descriptor again.

subscribe(c,'notification');
data = read(d)

data = 1×2

     1     0