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Bluetooth Low Energy characteristics handle data read and write. More...

Import Statement: import Felgo 4.0
Since: Felgo 3.7.0



  • readWriteError(string characteristicName, string characteristicUuid, BluetoothLeCharacteristic::CharacteristicReadWriteError error)


  • void read()
  • void write(ArrayBuffer data, QLowEnergyService::WriteMode writeMode)

Detailed Description

General info and usage examples for Bluetooth LE: Use Bluetooth Low Energy

Bluetooth Low Energy characteristics are the actual logical input and output nodes for data transfer. The BluetoothLeCharacteristic provides a simple way to describe, read and write characteristics. Notifications are set automatically so value updates trigger QML signals and bindigs.

Declaring Characteristics in QML ahead of time allows the definition of helper functions for formating, data parsing, and handling signals.

This is an example for a read write string in a custom characteristic.

 BluetoothLeCharacteristic {
   id: stringCharacteristic
   uuid: '{beb5483e-36e1-4688-b7f5-ea07361b26a8}'
   dataFormat: 0x19

   function formatWrite(text) {
     let data = new Uint8Array(text.length)
     for (var i = 0; i < text.length; i++) {
         data[i] = text.charCodeAt(i)

   onValidChanged: {
     // Read initial value once characteristic is valid
     if (valid) {

Property Documentation

CharacteristicReadWriteError : enumeration

Possible error values for characteristic read or write. For example if a the property PropertyType.Read is not set, the readWriteError signal will be emitted with the value CharacteristicReadWriteError.ReadNotAllowed.

  • CharacteristicReadWriteError.NoError
  • CharacteristicReadWriteError.ReadNotAllowed
  • CharacteristicReadWriteError.WriteNotAllowed

PropertyType : enumeration

Characteristic property definitions, properties describe operation permissions for the containing characteristic.

  • PropertyType.Unknown
  • PropertyType.Broadcasting
  • PropertyType.Read
  • PropertyType.WriteNoResponse
  • PropertyType.Write
  • PropertyType.Notify
  • PropertyType.Indicate
  • PropertyType.WriteSigned
  • PropertyType.ExtendedProperty

See also BluetoothLeCharacteristic::properties and QLowEnergyCharacteristic::PropertyType.

dataFormat : int

Some characteristics provide the Characteristic Presentation Format descriptor that carries the format that the value uses, in most cases is missing and should be provided via a XML BluetoothLE profile. It can also be set here as an int value. If a dataFormat value is set, an automatic convertion is used for unsigned and string values, providing the result in the value property. The default value is -1.

Some common formats are:

  • 0x01 boolean
  • 0x04 uint8
  • 0x06 uint16
  • 0x08 uint32
  • 0x0A uint64
  • 0x0C int8
  • 0x0E int16
  • 0x10 int32
  • 0x12 int64
  • 0x14 float 32bit
  • 0x15 float 64bit
  • 0x19 sting utf-8
  • 0x1A string utf-16

descriptors : var

A list of objects containing the descriptors values for the characteristic, each descriptor contains a string name, a string uuid and a var value.

name : string

Name of the characteristic reported by the remote device, if the device does report and empty name it's possible to set this value with the fallback name.

properties : BluetoothLeCharacteristic::PropertyTypes

Holds the property flags for the characteristic.

This is a test of the characteristic read permission.

 BluetoothLeCharecteristic {
   Component.onCompleted: {
     var canRead = properties.indexOf(BluetoothLeCharecteristic.Read) > -1;

Note: If the characteristic descriptors contain the PropertyType.Notify, the BluetoothLeDevice sends automatically a descriptor write to enable notifications. Value updates from the remote device will trigger QML bindings to the corresponding characteristic value.

uuid : var

Reading the uuid will always return the long 128bit string formated value as "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' is a hex digit. A short 16bit uuid can be set using the 0xXXXX notation for standard characteristics defined by the Bluetooth SIG.

valid : bool

Set if a valid characteristic is discovered for the current uuid.

value : var

The value of the characteristic parsed using the dataFormat provided. This property returns undefined if the dataFormat property is not set.

valueBase64 : string

A base64 encoded string of the raw binary data value.

valueRaw : ArrayBuffer

The raw binary value as an ArrayBuffer.

Signal Documentation

readWriteError(string characteristicName, string characteristicUuid, BluetoothLeCharacteristic::CharacteristicReadWriteError error)

A read or write error was emitted durint read or write. For example trying to read a characteristic that does not allow reading.

Note: The corresponding handler is onReadWriteError.

Method Documentation

void read()

Requests a characteristic read, the characteristic value is updated if the read is successful, otherwise a readWriteError signal will be emitted.

void write(ArrayBuffer data, QLowEnergyService::WriteMode writeMode = QLowEnergyService::WriteWithResponse)

Starts a characteristic write with the given data. If the remote device has notifications enabled, the value is updated as soon as the device receives the write request. You can also request a read after writing to the characteristic, as long as the characteristic has a property allowing the writeMode.

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