I'm trying to send data to an Arduino via a serial communication. I'm using a buffer to store bytes I'd like to send and then use the fwrite command to write them to serial.
Sender (Matlab)
disp(bufferSend);
fwrite(xbee,bufferSend,'uint8');
disp('sent:');
xbee.ValuesSent
the display command shows that 255 bytes hav2 been sent:
2 1 0 0 0 1 1 13 17 0 30 0 12 14 0 0 0 1 0
[...] 0 0 0 [...] 0
sent:
255
Receiver (Arduino)
the received values are correct till the 7-th byte. Only 70 bytes are received;
The Arduino serial monitor prints one byte at the time with the following code:
byte getData;
[...]
while(xbee.available()>0)
{
getData = xbee.read();
Serial.print("Received: ");
Serial.print(getData);
Serial.print(" Bin: ");
Serial.print(getData,BIN);
Serial.print(" Hex: ");
Serial.print(getData,HEX);
Serial.print(" cont: ");
Serial.print(cont);
Serial.println();
[...]
}
Here is the output:
Matlab communication established.
Received: 2 Bin: 10 Hex: 2 cont: 2
Received: 1 Bin: 1 Hex: 1 cont: 3
Received: 0 Bin: 0 Hex: 0 cont: 4
Received: 0 Bin: 0 Hex: 0 cont: 5
Received: 0 Bin: 0 Hex: 0 cont: 6
Received: 1 Bin: 1 Hex: 1 cont: 7
Received: 1 Bin: 1 Hex: 1 cont: 8
Received: 141 Bin: 10001101 Hex: 8D cont: 9
Received: 145 Bin: 10010001 Hex: 91 cont: 10
Received: 128 Bin: 10000000 Hex: 80 cont: 11
Received: 143 Bin: 10001111 Hex: 8F cont: 12
Received: 128 Bin: 10000000 Hex: 80 cont: 13
Received: 134 Bin: 10000110 Hex: 86 cont: 14
Received: 135 Bin: 10000111 Hex: 87 cont: 15
Received: 128 Bin: 10000000 Hex: 80 cont: 16
Received: 128 Bin: 10000000 Hex: 80 cont: 17
Received: 128 Bin: 10000000 Hex: 80 cont: 18
Received: 128 Bin: 10000000 Hex: 80 cont: 19
Received: 128 Bin: 10000000 Hex: 80 cont: 20
Received: 128 Bin: 10000000 Hex: 80 cont: 21
Received: 128 Bin: 10000000 Hex: 80 cont: 22
Received: 128 Bin: 10000000 Hex: 80 cont: 23
Received: 128 Bin: 10000000 Hex: 80 cont: 24
Received: 128 Bin: 10000000 Hex: 80 cont: 25
Received: 128 Bin: 10000000 Hex: 80 cont: 26
Received: 128 Bin: 10000000 Hex: 80 cont: 27
Received: 128 Bin: 10000000 Hex: 80 cont: 28
Received: 128 Bin: 10000000 Hex: 80 cont: 29
Received: 128 Bin: 10000000 Hex: 80 cont: 30
Received: 128 Bin: 10000000 Hex: 80 cont: 31
Received: 128 Bin: 10000000 Hex: 80 cont: 32
Received: 128 Bin: 10000000 Hex: 80 cont: 33
Received: 128 Bin: 10000000 Hex: 80 cont: 34
Received: 64 Bin: 1000000 Hex: 40 cont: 35
Received: 64 Bin: 1000000 Hex: 40 cont: 36
Received: 64 Bin: 1000000 Hex: 40 cont: 37
Received: 64 Bin: 1000000 Hex: 40 cont: 38
Received: 64 Bin: 1000000 Hex: 40 cont: 39
Received: 64 Bin: 1000000 Hex: 40 cont: 40
Received: 64 Bin: 1000000 Hex: 40 cont: 41
Received: 64 Bin: 1000000 Hex: 40 cont: 42
Received: 64 Bin: 1000000 Hex: 40 cont: 43
Received: 64 Bin: 1000000 Hex: 40 cont: 44
Received: 64 Bin: 1000000 Hex: 40 cont: 45
Received: 64 Bin: 1000000 Hex: 40 cont: 46
Received: 64 Bin: 1000000 Hex: 40 cont: 47
Received: 64 Bin: 1000000 Hex: 40 cont: 48
Received: 64 Bin: 1000000 Hex: 40 cont: 49
Received: 64 Bin: 1000000 Hex: 40 cont: 50
Received: 64 Bin: 1000000 Hex: 40 cont: 51
Received: 64 Bin: 1000000 Hex: 40 cont: 52
Received: 64 Bin: 1000000 Hex: 40 cont: 53
Received: 64 Bin: 1000000 Hex: 40 cont: 54
Received: 64 Bin: 1000000 Hex: 40 cont: 55
Received: 64 Bin: 1000000 Hex: 40 cont: 56
Received: 64 Bin: 1000000 Hex: 40 cont: 57
Received: 64 Bin: 1000000 Hex: 40 cont: 58
Received: 64 Bin: 1000000 Hex: 40 cont: 59
Received: 32 Bin: 100000 Hex: 20 cont: 60
Received: 32 Bin: 100000 Hex: 20 cont: 61
Received: 32 Bin: 100000 Hex: 20 cont: 62
Received: 32 Bin: 100000 Hex: 20 cont: 63
Received: 32 Bin: 100000 Hex: 20 cont: 64
Received: 0 Bin: 0 Hex: 0 cont: 65
Received: 0 Bin: 0 Hex: 0 cont: 66
Received: 0 Bin: 0 Hex: 0 cont: 67
Received: 0 Bin: 0 Hex: 0 cont: 68
Received: 0 Bin: 0 Hex: 0 cont: 69
Received: 0 Bin: 0 Hex: 0 cont: 70
Received: 0 Bin: 0 Hex: 0 cont: 71
[...]
If the eigth value (i.e 13) is placed in the first positions on the buffer, Arduino receives it correctly.
Is it related to the fwrite function and buffer dimensions? Is it a case of buffer overflow?
Solution
Slow down the Baudrate! In my case 19200 worked
This looks like a hardware issue. It appears that the bits of the the values are getting corrupted.
141 is 13 with the first bit flipped
145 is 17 with the first bit flipped
128 is 0 with the first bit flipped
143 is 30 shifted right, and the first bit flipped
You haven't said how the matlab is connected to xbee. Could the problem be incompatible voltage levels or baudrate? A problem like this would show symptoms of the first bytes being okay, and then later the bytes go bad as the communication gets out of sync. If this were the problem, then the errors would appear with some randomness. Are the received values always the same for a given set of bytes?
The communication between the xbee modules is probably okay, as there should be a checksum involved to make sure the packets are not corrupted.
That leaves the serial communication between matlab and the first xbee, and the serial communication between the shield and the arduino.
You can also try a Serial.readBytes() call to see if that makes a difference.