CAN bus filtering specified data

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1

Working on a project using UNO + NiRen mcp2515 shield.
Its my first CAN experience, so it took some time to make it work, and finally i got data using CoryJFowler library. Good thing i have Canhacker so that helped me alot with checking and searching values im interested in.
Terminal:
Standard ID: 0x608 DLC: 8 Data: 0x7C 0x42 0xFC 0x6D 0x70 0x00 0x00 0x00
Thats the line im interested but main thing is to separate first data bytes (same as a DLC: 1) 0x7C.
Thats a temp value, so need print it to terminal withought all others. Im novice and looks hard to manage program code.

Using Cory's receive example i almost did all i want with lack of knowledge.
It takes first data bytes to terminal once id:608 packed is received and then value stuck even it changes realtime i always see the 1st received value (doesnt update). Another thing my filter not very correct and it loads CPU.

Code im using:

// CAN Receive Example
//

#include <mcp_can.h>
#include <SPI.h>

long unsigned int rxId;
unsigned char len = 0;
unsigned char rxBuf[8];
char msgString[128];                        // Array to store serial string
long unsigned int T=0;

#define CAN0_INT 2                              // Set INT to pin 2
MCP_CAN CAN0(10);                               // Set CS to pin 10


void setup()
{
  Serial.begin(115200);
  
  // Initialize MCP2515 running at 16MHz with a baudrate of 500kb/s and the masks and filters disabled.
  if(CAN0.begin(MCP_ANY, CAN_500KBPS, MCP_8MHZ) == CAN_OK)
 
  CAN0.setMode(MCP_NORMAL);                     // Set operation mode to normal so the MCP2515 sends acks to received data.

  pinMode(CAN0_INT, INPUT);                            // Configuring pin for /INT input
  

}

void loop()
{
  if(!digitalRead(CAN0_INT))                         // If CAN0_INT pin is low, read receive buffer
  {
    CAN0.readMsgBuf(&rxId, &len, rxBuf);      // Read data: len = data length, buf = data byte(s)

    if(rxId  == 0x608){   
       for(byte i = 0; i<len; i){
      //  sprintf(msgString, " %.2X", rxBuf[i]);
        T=(rxBuf[i]-40);
         Serial.println(T);
              delay(1000);
               
      }
    } 
  } 
}

/*********************************************************************************************************
  END FILE
*********************************************************************************************************/

Thanks in advance

2

Try changing

for(byte i = 0; i<len; i){

to

for(byte i = 0; i<len; i++){

for a start.

Its possible you are reading the bus too often but I dont know enough about the CAN_INT0 signal to be sure- it may be that you only need to read a message when the pin changes state, not whenever its LOW.

3

in Cory's example it's i++,
so when i leave it as is:
94
28
212
69
72
4294967256
4294967256
4294967256
94
28
212
69
72
4294967256
4294967256
4294967256

94 is correct temperature
all other is single bytes goes threw T=(rxBuf*-40);*

4

If you only want the first byte then no need for the loop. Change

for(byte i = 0; i<len; i){
      //  sprintf(msgString, " %.2X", rxBuf[i]);
        T=(rxBuf[i]-40);
         Serial.println(T);
              delay(1000);
               
      }

to just print out the first byte.

    T=(rxBuf[0]-40);
    Serial.println(T);
    delay(1000);
5

Thanks for mr. rw950431
Working correctly, with live updating readed out value