Android Question How do I read data from a service address UUID and characteristic UUID using the BLE2 library?

[seskindell]

I connect to the device ok ...

Now, how do I read data from service: "0000ffa0-0000-1000-8000-00805f9b34fb"
at the characteristic: "0000ffa3-0000-1000-8000-00805f9b34fb"

The examples I seen use ble and not ble2
I have NO idea where the library ble is at .. it is not in my Libraries for the latest version of B4A.

 

[JordiCP]

Can you describe what you are trying or add your code?

Once you start the scan, must wait for the xxx_DeviceFound event to be fired. Then try to connect to the specific device and wait for the xxx_Connected event.
Only then, you can try to read services and characteristics with

myBLE.ReadData( myServiceString )
'or
myBLE.ReadData2( myServiceString, myCharacteristicString )

and if it works, receive the data in xxx_DataAvailable event.

 

[seskindell]

Can you describe what you are trying or add your code?

Once you start the scan, must wait for the xxx_DeviceFound event to be fired. Then try to connect to the specific device and wait for the xxx_Connected event.
Only then, you can try to read services and characteristics with

myBLE.ReadData( myServiceString )
'or
myBLE.ReadData2( myServiceString, myCharacteristicString )

and if it works, receive the data in xxx_DataAvailable event.

Thank you!

The readdata2 seems to work good. Can you give me an example of what I need to include for the DataAvailable event (and to parse out the data).

I'm trying to read the x,y,z coordinates of an accel.

- Steve

 

[JordiCP]

It depends on how your BLE device specifically serves the data for that characteristic. For instance, it can be one byte for each axis, or a string representation...do you have any documentation of this sensor?

 

[seskindell]

Hi Jordi,

I was able to output the results for the x,y,z axis .. I'm not sure how to parse it out. I will look for the documentation on the sensor.

Here is the output:
0000ffa1-Accel Enable
0000ffa0-0000-1000-8000-00805f9b34fb
(MyMap) {0000ffa1-0000-1000-8000-00805f9b34fb=[B@3f6528c4, 0000ffa2-0000-1000-8000-00805f9b34fb=[B@2a996fb, 0000ffa3-0000-1000-8000-00805f9b34fb=[B@f57f318, 0000ffa4-0000-1000-8000-00805f9b34fb=[B@31140171, 0000ffa5-0000-1000-8000-00805f9b34fb=[B@c5b3b56}

0000ffa2-Accel Range
0000ffa0-0000-1000-8000-00805f9b34fb
(MyMap) {0000ffa1-0000-1000-8000-00805f9b34fb=[B@3f6528c4, 0000ffa2-0000-1000-8000-00805f9b34fb=[B@1c1643ad, 0000ffa3-0000-1000-8000-00805f9b34fb=[B@f57f318, 0000ffa4-0000-1000-8000-00805f9b34fb=[B@31140171, 0000ffa5-0000-1000-8000-00805f9b34fb=[B@c5b3b56}

0000ffa3-x axis coord.
0000ffa0-0000-1000-8000-00805f9b34fb
(MyMap) {0000ffa1-0000-1000-8000-00805f9b34fb=[B@3f6528c4, 0000ffa2-0000-1000-8000-00805f9b34fb=[B@1c1643ad, 0000ffa3-0000-1000-8000-00805f9b34fb=[B@2e7b6e2, 0000ffa4-0000-1000-8000-00805f9b34fb=[B@31140171, 0000ffa5-0000-1000-8000-00805f9b34fb=[B@c5b3b56}

0000ffa4-y axis coord.
0000ffa0-0000-1000-8000-00805f9b34fb
(MyMap) {0000ffa1-0000-1000-8000-00805f9b34fb=[B@3f6528c4, 0000ffa2-0000-1000-8000-00805f9b34fb=[B@1c1643ad, 0000ffa3-0000-1000-8000-00805f9b34fb=[B@2e7b6e2, 0000ffa4-0000-1000-8000-00805f9b34fb=[B@2b2dea73, 0000ffa5-0000-1000-8000-00805f9b34fb=[B@c5b3b56}

0000ffa5-z axis coord.
0000ffa0-0000-1000-8000-00805f9b34fb
(MyMap) {0000ffa1-0000-1000-8000-00805f9b34fb=[B@3f6528c4, 0000ffa2-0000-1000-8000-00805f9b34fb=[B@1c1643ad, 0000ffa3-0000-1000-8000-00805f9b34fb=[B@2e7b6e2, 0000ffa4-0000-1000-8000-00805f9b34fb=[B@2b2dea73, 0000ffa5-0000-1000-8000-00805f9b34fb=[B@27ee0d30}

 

[JordiCP]

Yes, it will be needed. Is it a commercial device?

Anyway, you can run the BLE example in the BLE2 library thread adapted to the exact device you want to connect and the service/characteristics to be read, or, if you are using your own implementation, log it to view its contents.

Sub xxx_DataAvailable (Service As String, Characteristics As Map)   'whatever xxx is
    ' Here we just log what is received
    For Each id As String In Characteristics.Keys
        Dim dataContent() as Byte = Characteristics.Get(id)

        ' If the values are string-formatted, convert the bytes to string
        ' Log( "Characteristic:"& id &": "&BytesToString(dataContent, 0, dataContent.Length, "UTF8") )

        ' Or, if we know that each byte has a meaning, just show the bytes 
        ' Dim bc as ByteConverter    '<---- will need the ByteConverter library
        ' Log( "Characteristic:"& id &": "& bc.HexFromBytes(dataContent) )
    Next
End Sub

 

[seskindell]

Yes, it will be needed. Is it a commercial device?

Anyway, you can run the BLE example in the BLE2 library thread adapted to the exact device you want to connect and the service/characteristics to be read, or, if you are using your own implementation, log it to view its contents.

Sub xxx_DataAvailable (Service As String, Characteristics As Map)   'whatever xxx is
    ' Here we just log what is received
    For Each id As String In Characteristics.Keys
        Dim dataContent() as Byte = Characteristics.Get(id)

        ' If the values are string-formatted, convert the bytes to string
        ' Log( "Characteristic:"& id &": "&BytesToString(dataContent, 0, dataContent.Length, "UTF8") )

        ' Or, if we know that each byte has a meaning, just show the bytes
        ' Dim bc as ByteConverter    '<---- will need the ByteConverter library
        ' Log( "Characteristic:"& id &": "& bc.HexFromBytes(dataContent) )
    Next
End Sub

Yes .. it is a small sensor from u-blox .. the OLP425

Thank you for you help.

- Steve

 

[JordiCP]

According to the documentation (at 6.1.0.0.3), seems that X-axis acceleration (FFA3) is encoded in a single byte with a range [-2G...2G]
Also states that the characteristic is notifiable, but you can always simply read its value.

Here comes the interpretation part
It is defined as 'int8' in the uBLox side, corresponding to [-2G...2G]. As in B4A bytes are also signed, unless a strange mapping is used, the conversion is direct, so you will have (not tested):

Sub xxx_DataAvailable (Service As String, Characteristics As Map)   'whatever xxx is
    ' Here we just log what is received
    For Each id As String In Characteristics.Keys
        Dim dataContent() as Byte = Characteristics.Get(id)

        ' Calculate X_axis acceleration if the read characteristic (id) is the 0000ffa3-..., or Y_axis if 0000ffa4, ....
        if id="0000ffa3-......"  Then  '<--fill with correct values 
           Dim X_accel_scaled as Byte = dataContent(0)
           Dim X_accel_final as Float = X_accel_scaled *2*9.8/127     ' Scale conversion : convert [-128..+127] to [-2G..+2G]
           Log( "X_accel value is: "& X_accel_final )
        End if   

    Next
End Sub

 

[seskindell]

Wow .. your a genius! Thank you so much!!!