Not able to send variable value through CAN bus shield with UNO

Using Arduino Programming Questions
1

Hi everybody,

I am trying to calculate the rotational speed of an encoder and than send the results on a CAN bus.

Hardware :
Arduino UNO
CAN-BUS shield V1.2 seeedstudio
USB to CAN dongle PEAK

Software:
Arduino IDE
PCAN-View

The baud rate is set at 500 kbit/s on both side.
I have the 120 ohms resistor

I have no problem calculating the speed of the encoder and displaying it with serial plotter. My problem is that I am not able to send the value of a variable through CAN. I am able to send a message and to read it in PCAN-View, but if I put a variable in my message I always got a value of 0 in PCAN-View.

with :

int test = 77;
unsigned char CAN_MSG[8] = {test, 0, 0, 0, 0, 0, 0, 0};
// send data:  id = 0x00, standard frame, data len = 8, stmp: data buf
CAN.sendMsgBuf(0x60, 0, 8, CAN_MSG);

I got : 4D 00 00 00 00 00 00 00

But if I tried to change the value of "test" in a script I always got : 00 00 00 00 00 00 00 00

2

CAN_MSG is an array of 8 chars.
a char is 8 bits

test is an integer which are 16 bits.

3

Thank you for the hint, I will investigate that this morning

4

I tried to play with the type of variables ( int, char, byte, etc..), but I am still stuck with the same problem.

The message send on the CAN bus is always the same one. It s always the first message on repeat.

After that, even if the value of the variable are changing I always got the first message.

5

I did a new test and apparently my program can change the value of the variable three times.

Example :

unsigned char stmp[8]= {0,0,0,0,0,0,0,0};
char test = 2;

void setup() {
 Serial.begin(250000);      // Serial com for data output
 
 initEncoders();       
 clearEncoderCount(); 

 //CAN bus initialisation
 while (CAN_OK != CAN.begin(CAN_500KBPS))              // init can bus : baudrate = 500k
    {
        Serial.println("CAN BUS Shield init fail");
        Serial.println(" Init CAN BUS Shield again");
        delay(100);
    }
 
}

void loop() {

test = test+1;
stmp[3] = test ;
 CAN.sendMsgBuf(0x07B, 0, 8, stmp);
 Serial.println(stmp[3]);
 delay(10);
}

In PCAN-View I receive the message :

00 00 00 03 00 00 00 00
00 00 00 04 00 00 00 00

and then :

00 00 00 05 00 00 00 00

until I restart the Arduino or resend the program. But if I use the serial plotter I can see the value of stmp[3] going from 0 to 255 and starting over.