Receiving Float From Arduino "BLEFloatCharacteristic" Via BLE

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4. Receiving float from Arduino "BLEFloatCharacteristic" via BLE

Forum Updated to NodeBB v4.3 + New Features Receiving float from Arduino "BLEFloatCharacteristic" via BLE Scheduled Pinned Locked Moved Solved General and Desktop 6 Posts 3 Posters 1.1k Views 3 Watching Oldest to Newest

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• G Offline G Offline giorgiogandolfi_ wrote on last edited by #1

  Hello everyone, I'm currently experiencing a problem while sending gyroscope and accelerometer data from an Arduino Sense BLE to a QT application.

  The code I wrote on Arduino creates a single service containing two characteristics, one for sending the gyro data and one for the accelerometer data. Each one of them is a "BLEFloatCharacteristic", so a float value should be sent.

  Using the notify property of BLE, I connected each one of the characteristic to the signal "characteristicChanged", as per own QT guide on BLE.

  connect(ptr_dataService, &QLowEnergyService::characteristicChanged, this, &MainWindow::updateGyroscopeData); connect(ptr_dataService, &QLowEnergyService::characteristicChanged, this, &MainWindow::updateAccelerometerData);

  The SLOTs to get the data are very basic:

  void MainWindow::updateGyroscopeData(const QLowEnergyCharacteristic &c, const QByteArray &value) { if (c.uuid() != QBluetoothUuid(BLE_UUID_GYROSCOPE_CHARACTERISTIC)) return; qDebug()<<"Gyro"; qDebug()<<value; } //------------------------------------------------------------------------------ void MainWindow::updateAccelerometerData(const QLowEnergyCharacteristic &c, const QByteArray &value) { if (c.uuid() != QBluetoothUuid(BLE_UUID_ACCELEROMETER_CHARACTERISTIC)) return; qDebug()<<"Acc"; qDebug()<<value; }

  What I get printed out is something like

  Gyro "\x00\x00z\xBF" Gyro "\x00\x00\xFA\xBD" Acc "\x00\x00\xDD<" Acc "\x00H^?"

  How can I get a float number instead? Thanks to everyone!

  1 Reply Last reply 0
• M Offline M Offline mpergand wrote on last edited by mpergand #2

  Hi,

  Warning: we enter the twillight zone :)

  To convert QByteArray to float, I tried this:

  float f=12.5; QByteArray d((char*)&f,sizeof(f)); float ff=*reinterpret_cast<float*>(d.data()); qDebug()<<ff;

  prints 12.5 so far so good but what is the format of the float you send from the Ardiuno, a 4 bytes float like in C ? Which endianess little/big endian ?

  First try to print the QByteArray in a readable format with: qDebug()<<value.toHex();

  [EDIT] Seems to be valid floats: -0.976563 giro 1 -0.12207 giro 2 0.0269775 acc 1 0.868774 acc2

  A 1 Reply Last reply 1
• G Offline G Offline giorgiogandolfi_ wrote on last edited by #3

  Yes, your suggestions worked to perfection, thank you very much!

  Adding only a small note for potential future viewers: because the functions I use to update gyro and accelerometer data get as argument

  const QByteArray &value

  I had to modify your suggestion in :

  float fNum = *reinterpret_cast<const float*>(value.constData()); 1 Reply Last reply 1
• M mpergand

  Hi,

  Warning: we enter the twillight zone :)

  To convert QByteArray to float, I tried this:

  float f=12.5; QByteArray d((char*)&f,sizeof(f)); float ff=*reinterpret_cast<float*>(d.data()); qDebug()<<ff;

  prints 12.5 so far so good but what is the format of the float you send from the Ardiuno, a 4 bytes float like in C ? Which endianess little/big endian ?

  First try to print the QByteArray in a readable format with: qDebug()<<value.toHex();

  [EDIT] Seems to be valid floats: -0.976563 giro 1 -0.12207 giro 2 0.0269775 acc 1 0.868774 acc2

  A Offline A Offline artwaw wrote on last edited by #4

  @mpergand What is wrong with QByteArray::toFloat() that you offer the above?

  For more information please re-read.

  Kind Regards, Artur

  M 1 Reply Last reply 0
• A artwaw

  @mpergand What is wrong with QByteArray::toFloat() that you offer the above?

  M Offline M Offline mpergand wrote on last edited by #5

  @artwaw As far as I know, it only works with ASCII string:

  char n[]="1.25"; QByteArray d(n); bool ok; float f=d.toFloat(&ok); qDebug()<<f<<ok; A 1 Reply Last reply 2
• M mpergand

  @artwaw As far as I know, it only works with ASCII string:

  char n[]="1.25"; QByteArray d(n); bool ok; float f=d.toFloat(&ok); qDebug()<<f<<ok; A Offline A Offline artwaw wrote on last edited by #6

  @mpergand thanks.

  For more information please re-read.

  Kind Regards, Artur

  1 Reply Last reply 0

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