Question

I’ve searched around but can’t find a solution to this problem. I’m using the simplest example I can think of to test this. This is the processing Code:

void setup() {     
  Serial.begin(9600);
} 

void loop() { 
  for(int i =48;i<51;i++)  {
    Serial.write(i);  //writes 0-2 in ascii and 48-51 in bytes. 
  }
}

If I view the output on the serial monitor it correctly prints “012012012012012012012” etc without any problems. I wrote a simple program in processing to view the data:

import processing.serial.*;
Serial myPort;  

void setup() { 
  String[] ports =Serial.list();
  myPort = new Serial(this, ports[1], 9600);
}

void draw() {
  if (myPort.available() >=10) 
  {   
    byte[] serialIn = new byte[10];
    myPort.readBytes(serialIn);
    for (int i =0;i<serialIn.length;i++)
    {
      println(serialIn[i] +" binary:"+ binary(serialIn[i]));
    }
  }
}

most of the time it prints junk:

-126   binary:10000010
-118   binary:10001010
-110   binary:10010010
-126   binary:10000010
-118   binary:10001010
-110   binary:10010010 

And occasionally it prints the correct values:

48   binary:00110000
49   binary:00110001
50   binary:00110010
48   binary:00110000
49   binary:00110001
50   binary:00110010                                                                

It looks like each byte gets shifted to the left by 3 bits although I can’t work out why it behaved differently each time I run the program. Interestingly, if I get the arduino to send 0,1,2 it never prints garbage.

Really I want to read the data in C#. This is the meat of the C# code which is based on this example:
http://msmvps.com/blogs/coad/archive/2005/03/23/SerialPort-_2800_RS_2D00_232-Serial-COM-Port_2900_-in-C_2300_-.NET.aspx

if (serialPort.BytesToRead >0)
{
  byte temp = (byte)serialPort.ReadByte();
  Console.WriteLine(temp +"\t binary: " +byte2Binary(temp));
}

It prints some of the correct values but often misses numbers and is interspersed with garbage:

130    binary: 10000010
138    binary: 10001010
48     binary: 00110000
49     binary: 00110001
50     binary: 00110010
146    binary: 10010010
49     binary: 00110001
50     binary: 00110010
49     binary: 00110001
50     binary: 00110010
146    binary: 10010010
49     binary: 00110001
50     binary: 00110010
48     binary: 00110000
138    binary: 10001010
146    binary: 10010010

The binary values of the incorrect data is exactly the same as the processing binary values. Here the 3 bit shift seems random during runtime instead of being consistent for each time I run. I have tried putting a delay of up to 200ms between sending serial commands. It helps a bit but I still get at least 10% junk data. I’m trying to run a control loop so the longest delay I can afford is 3ms.
What can I do to fix this?

Thanks

Answer 1

If I view the output on the serial monitor it correctly prints

And occasionally it prints the correct values:

This points at a misconfiguration, try 4800 baud for instance. And maybe check the other properties (stopbits, handshake).