B4R Question How to GetBytes

[canalrun]

I am using the Serial Connector Tutorial to build a plotting window. Works great except ... I don't think I am using GetBytes properly.

I thought the follow two snippets would give the same buf():

Dim spts As String = "plot=0.9,0.6,0.3,0.1,0.2,0.3,0.4,0.5,0.6"
Dim buf() As Byte = spts.GetBytes

and

Dim buf() As Byte = Array As Byte( _
  0x70,0x6c,0x6f,0x74,0x3d,0x30,0x2e,0x39,0x2c,0x30, _
  0x2e,0x36,0x2c,0x30,0x2e,0x33,0x2c,0x30,0x2e,0x31, _
  0x2c,0x30,0x2e,0x32,0x2c,0x30,0x2e,0x33,0x2c,0x30, _
  0x2e,0x34,0x2c,0x30,0x2e,0x35,0x2c,0x30,0x2e,0x36)

The second one gives what I expect, the first doesn't.

What am i doing wrong?

Barry

 

[Erel]

What is the expected value? What is the purpose of this array?

 

[canalrun]

I am basically using your serial connector tutorial.

When the serial connector communicates between the Arduino and B4J application it wants to send a buffer of bytes rather than a string.

What I would like to do is send the string, "plot=0.9,0.6,0.3,0.1,0.2,0.3,0.4,0.5,0.6", encoded as a buffer of bytes, to my B4J application from the Arduino. My B4J application will recognize this as a command to plot the nine values on a bar graph.

The buffer of bytes it should send is equivalent to: (the data below is just the string above encoded as bytes)

Dim buf() As Byte = Array As Byte( _
  0x70,0x6c,0x6f,0x74,0x3d,0x30,0x2e,0x39,0x2c,0x30, _
  0x2e,0x36,0x2c,0x30,0x2e,0x33,0x2c,0x30,0x2e,0x31, _
  0x2c,0x30,0x2e,0x32,0x2c,0x30,0x2e,0x33,0x2c,0x30, _
  0x2e,0x34,0x2c,0x30,0x2e,0x35,0x2c,0x30,0x2e,0x36)

But, within B4J I can look at the actual buffer that is received when I encode the string using GetBytes (or the byte converter equivalent). It looks like the data was read from some random location in memory – not even close to what it should be. (kind of like a pointer error).

My B4J plot application works if I send the explicitly defined buf() shown just above.
But, just replacing my explicitly defined buf() with:

dim str as string = "plot=0.9,0.6,0.3,0.1,0.2,0.3,0.4,0.5,0.6"
dim buf() as byte = str.GetBytes

it does not work.

The question boils down to, "how do I convert a string to a buffer of bytes?"

I tried GetBytes, but that doesn't seem to work or I'm not using it correctly.

Barry.

 

[Erel]

Your B4R code is correct.

dim str as string = "plot=0.9,0.6,0.3,0.1,0.2,0.3,0.4,0.5,0.6"
dim buf() as byte = str.GetBytes

You can check it with Log(buf).

 

[canalrun]

Hello,
Thanks.

If the code looks correct, I just thought of something else that may be causing the problem.

I keep saying Arduino, but I'm actually using a WeMos D1 R2. I have run the B4R Blink tutorial and the unmodified Serial Connector tutorial – they both work fine.

But I'm wondering if this is due to some strange incompatibility. Tomorrow I will try this on my Arduino Mega board.

Is there another way I could iterate along each character of a string and copy the value into a byte buffer – maybe using a for loop?

I was looking for the str.charat() method, but this seems to not exist in B4R.

Barry.

 

[Erel]

String.CharAt is equivalent to:

Dim str() As Byte = "abc"
For i = 0 To str.Length - 1
 Log(str(i))
Next

Make sure to go over this tutorial: Strings and Bytes

 

[canalrun]

Thanks.

I tried with the Arduino Mega today - same code works.

The problem must be related to a WeMos D1 R2 difference.

Here is the output of my B4J modified Serial Connector:

Here is the relevant B4R Code:

Sub Astream_NewData (Buffer() As Byte)
  Dim cb() As Byte = "go"

  If (cmpBytes(Buffer, cb)) Then
      Dim lm() As Byte = "log=Got go"
    Log (lm)
   
    Dim buf() As Byte = "plot=0.9,0.6,0.3,0.1,0.2,0.3,0.4,0.5,0.6"
    Log(buf)
  Else
    Log(Buffer)
  End If
End Sub

I find it sometimes easier to visualize data as a graph (FFT output for example)

I will post all the source code later.

Barry.

 

[canalrun]

I have uploaded the source for the Serial Connector Graph to:
https://www.b4x.com/android/forum/threads/serial-connector-graph.67174/

Barry.

 

[Erel]

Note that you don't need to use cmpBytes. You can write If Buffer = cb Then ...