Arduino CanBus data HEX to DEC

remay66 · April 19, 2022, 1:50pm

Hello,

The project is to decode with a CAN bus data received by a sensor via an Arduino Mega card.
I have the following program everything works I can read the data frames in Hexadecimal.

What I want is to isolate in this frame the bytes 1-2 (humidity) 3-4 (temperature) 5-6 (C02) currently in hex
and convert them in real time to decimal

I am interested here to replace for example the "9C 25" by 22 degrees converted into decimal, it is necessary to reverse in "25 9C" because of the MSB LSB also.

I saw on the internet that there would be functions like strtoul() by writing this way " nResult= (nResult << 8) | (strtoul(pch, NULL, 16) & 0xff); "
but I don't really understand.

My actual code :

#include <SPI.h>
#include <SD.h>
#include <mcp_can.h>
#include "mcp2515_can.h"

File myFile;

#define CAN_2515

const int SPI_CS_PIN = 53;
const int CAN_INT_PIN = 2;

mcp2515_can CAN(SPI_CS_PIN); // Set CS pin

unsigned char flagRecv = 0;
unsigned char len = 0;
unsigned char buf[8];
char str[20];


void setup() 
{
    SERIAL_PORT_MONITOR.begin(115200);                                              // screen rate Arduino monitor
    attachInterrupt(digitalPinToInterrupt(CAN_INT_PIN), MCP2515_ISR, FALLING);      // start interrupt
    
    while (CAN_OK != CAN.begin(CAN_500KBPS))                                        // init can bus : baudrate = 500k
    {                                      
    SERIAL_PORT_MONITOR.println("CAN init fail, retry...");
    delay(100);
    }
    SERIAL_PORT_MONITOR.println("CAN init ok!");
    
    if (!SD.begin(4)) 
    {
        SERIAL_PORT_MONITOR.println("SD init fail!");
        while (1);
    }
    SERIAL_PORT_MONITOR.println("SD init OK.");
}

void MCP2515_ISR() { flagRecv = 1;}

void loop() {
    if (flagRecv) {                     // check if get data

        flagRecv = 0;                   // clear flag
        unsigned long id = 0; 

        myFile = SD.open("can.csv", FILE_WRITE);

            while (CAN_MSGAVAIL == CAN.checkReceive()) {
            CAN.readMsgBufID(&id, &len, buf);       // read data,  len: data length, buf: data buf

            SERIAL_PORT_MONITOR.print(id);
            SERIAL_PORT_MONITOR.print(",");
            
            myFile.print(id);
            myFile.print(",");

            for (int i = 0; i < len; i++) {
              
                SERIAL_PORT_MONITOR.print(buf[i]);
                SERIAL_PORT_MONITOR.print(",");

                myFile.print(buf[i]);
                myFile.print(",");

       }
            SERIAL_PORT_MONITOR.println();
            myFile.println();
        }

        myFile.close();
    }
}

// END FILE

Look forward to your replies, thanks.

kolaha · April 19, 2022, 2:17pm

#include <SPI.h>
#include <SD.h>
#include <mcp_can.h>
#include "mcp2515_can.h"

File myFile;

#define CAN_2515

const int SPI_CS_PIN = 53;
const int CAN_INT_PIN = 2;

mcp2515_can CAN(SPI_CS_PIN); // Set CS pin

unsigned char flagRecv = 0;
unsigned char len = 0;
unsigned char buf[8];
char str[20];


void setup() {
  SERIAL_PORT_MONITOR.begin(115200);                                              // screen rate Arduino monitor
  attachInterrupt(digitalPinToInterrupt(CAN_INT_PIN), MCP2515_ISR, FALLING);      // start interrupt

  while (CAN_OK != CAN.begin(CAN_500KBPS)) {                                      // init can bus : baudrate = 500k
    SERIAL_PORT_MONITOR.println("CAN init fail, retry...");
    delay(100);
  }
  SERIAL_PORT_MONITOR.println("CAN init ok!");

  if (!SD.begin(4))  {
    SERIAL_PORT_MONITOR.println("SD init fail!");
    while (1);
  }
  SERIAL_PORT_MONITOR.println("SD init OK.");
}

void MCP2515_ISR() {
  flagRecv = true;
}

void loop() {
  if (flagRecv) {                     // check if get data
    flagRecv = false;                   // clear flag
    unsigned long id = 0;

    while (CAN_MSGAVAIL == CAN.checkReceive()) {
      CAN.readMsgBufID(&id, &len, buf);       // read data,  len: data length, buf: data buf

      myFile = SD.open("can.csv", FILE_WRITE);
      myFile.print(id);
      myFile.print(",");

      for (int i = 0; i < len; i++) {
        myFile.print(buf[i]);
        myFile.print(",");
      }
      myFile.println();
      myFile.close();

      SERIAL_PORT_MONITOR.print(id);
      SERIAL_PORT_MONITOR.print(",");

      SERIAL_PORT_MONITOR.print(16 * buf[1] + buf[0], DEC);
      SERIAL_PORT_MONITOR.print(",");
      SERIAL_PORT_MONITOR.print(16 * buf[3] + buf[2], DEC);
      SERIAL_PORT_MONITOR.print(",");
      SERIAL_PORT_MONITOR.print(16 * buf[5] + buf[4], DEC);
      SERIAL_PORT_MONITOR.println();
    }
  }
}// END FILE

remay66 · April 19, 2022, 2:40pm

Thx Kolaha , but how can I retrieve the decimal value of this line of code in order to convert it by doing: "decimal value "x scale + offset

SERIAL_PORT_MONITOR.print(16 * buf[3] + buf[2], DEC);
                  SERIAL_PORT_MONITOR.print(",");

Thx so mutch for your help.

kolaha · April 19, 2022, 2:46pm

mark my sketch as solution

I don't see in sketch any "x scale" or "offset"

remay66 · April 19, 2022, 3:05pm

yes I used your code but I miss a step before finishing, how to recover the decimal value of bytes 3 2 ? maybe " comment at the bottom of the code ".

Cordially.


#include <SPI.h>
#include <SD.h>
#include "mcp2515_can.h"

File myFile;

#define CAN_2515

const int SPI_CS_PIN = 53;
const int CAN_INT_PIN = 2;

mcp2515_can CAN(SPI_CS_PIN); // Set CS pin

unsigned char flagRecv = 0;
unsigned char len = 0;
unsigned char buf[8];
char str[20];

int Offset = 273 ;
int Scale = 0.3125 ;

void setup() 
{
    SERIAL_PORT_MONITOR.begin(115200);                                              // screen rate Arduino monitor
    attachInterrupt(digitalPinToInterrupt(CAN_INT_PIN), MCP2515_ISR, FALLING);      // start interrupt
    
    while (CAN_OK != CAN.begin(CAN_500KBPS))                                        // init can bus : baudrate = 500k
    {                                      
    SERIAL_PORT_MONITOR.println("CAN init fail, retry...");
    delay(100);
    }
    SERIAL_PORT_MONITOR.println("CAN init ok!");
    
    if (!SD.begin(4)) 
    {
        SERIAL_PORT_MONITOR.println("SD init fail!");
        while (1);
    }
    SERIAL_PORT_MONITOR.println("SD init OK.");
}

void MCP2515_ISR() { flagRecv = 1;}

void loop() {
    if (flagRecv) {                     // check if get data

        flagRecv = 0;                   // clear flag
        unsigned long id = 0; 

            while (CAN_MSGAVAIL == CAN.checkReceive()) {
            CAN.readMsgBufID(&id, &len, buf);       // read data,  len: data length, buf: data buf
            
            myFile = SD.open("can.csv", FILE_WRITE);
            myFile.print(id);
            myFile.print(",");
            
                for (int i = 0; i < len; i++) {
                myFile.print(buf[i]);
                myFile.print(",");
                }

                myFile.println();
                myFile.close();
                 
                  SERIAL_PORT_MONITOR.print(id);
                  SERIAL_PORT_MONITOR.print(",");

                  SERIAL_PORT_MONITOR.print(16 * buf[1] + buf[0], DEC);
                  SERIAL_PORT_MONITOR.print(",");
                  
                  SERIAL_PORT_MONITOR.print(16 * buf[3] + buf[2], DEC);
                  SERIAL_PORT_MONITOR.print(",");

                  // i want to do this conversion " Temperature = Value DEC buf[3]+buf[2] x Scale - Offset "  but how can i retrieve the value of byte 3 2 DEC to do that.
                  
                  SERIAL_PORT_MONITOR.print(16 * buf[5] + buf[4], DEC);
                  SERIAL_PORT_MONITOR.println();
    }
  }
}// END FILE

kolaha · April 19, 2022, 3:08pm

mark as solution

kolaha · April 19, 2022, 3:10pm

SERIAL_PORT_MONITOR.print( buf[3], DEC);
SERIAL_PORT_MONITOR.print( buf[2], DEC);

remay66 · April 19, 2022, 3:15pm

Can i do to convert my decimal value ? :

A = SERIAL_PORT_MONITOR.print(16 * buf[3] + buf[2], DEC);
Temperature = A x Scale + Offset;
SERIAL_PORT_MONITOR.println();

I mark you as solution after that of course

kolaha · April 19, 2022, 3:33pm

unsigned int A = 16 * buf[3] + buf[2];
Temperature = A * Scale + Offset;
SERIAL_PORT_MONITOR.println();

remay66 · April 20, 2022, 8:55am

Hello,

The project is to decode with a CAN bus data received by a sensor via an Arduino Mega card.
I have the following program everything works I can read the data frames in Hexadecimal.

What I want is to isolate in this frame the bytes 1-2 (humidity) 3-4 (temperature) 5-6 (C02) currently in hex and convert them in real time to decimal :

for exemple i receive :

" Get data from ID: 0x18FF0AEB
-> 5D AF 9C 25 64 0 64 0 "

I am interested here to replace for example the "9C 25" by 22 degrees converted into decimal, it is necessary to reverse in "25 9C" because of the MSB LSB also.

but I don't really understand how to to that

My actual code :

#include <SPI.h>
#include "mcp2515_can.h"
#define CAN_2515

const int SPI_CS_PIN = 53;
const int CAN_INT_PIN = 2;
mcp2515_can CAN(SPI_CS_PIN); 
                         
void setup() {
    SERIAL_PORT_MONITOR.begin(115200);

    while (CAN_OK != CAN.begin(CAN_500KBPS)) {             // init can bus : baudrate = 500k
        SERIAL_PORT_MONITOR.println("CAN init fail, retry...");
        delay(100);
    }
    SERIAL_PORT_MONITOR.println("CAN init ok!");
}


void loop() {
    unsigned char len = 0;
    unsigned char buf[8];

    if (CAN_MSGAVAIL == CAN.checkReceive()) {         // check if data coming
        CAN.readMsgBuf(&len, buf);    // read data,  len: data length, buf: data buf

        unsigned long canId = CAN.getCanId();

        SERIAL_PORT_MONITOR.println("-----------------------------");
        SERIAL_PORT_MONITOR.print("Get data from ID: 0x");
        SERIAL_PORT_MONITOR.println(canId, HEX);

        for (int i = 0; i < len; i++) { // print the data
            SERIAL_PORT_MONITOR.print(buf[i], HEX);
            SERIAL_PORT_MONITOR.print("\t");
        }
        SERIAL_PORT_MONITOR.println();
    }
}

Thx for your help

red_car · April 20, 2022, 9:19am

I don't understand how 22 is represented by this HEX number. Can you explain?

horace · April 20, 2022, 9:19am

this appears to be a copy of this arduino-canbus-data-hex-to-dec post

remay66 · April 20, 2022, 9:23am

yeah , 9𝐶 25 = 𝑏𝑦𝑡𝑒𝑠 34 they are reverse LSB MSB so 43 = 0𝑥259𝐶 = 𝟗𝟔𝟐𝟖 in decimal

temperature = decimal value ×𝑺𝒄𝒂𝒍𝒆+𝑶𝒇𝒇𝒔𝒆𝒕

For our test we obtain: 9628 ×0.3125 −273=𝟐𝟕 °𝐂

The average ambient temperature being 22 degrees, it is possible that the electronic components of the sensor heat up during the test time.

remay66 · April 20, 2022, 9:27am

yes but this solution gives me weird values like:

419367915,3011,686,198

i dont understand because in hexa i have > AE 92 25 10 07 5F

with this part of code :

SERIAL_PORT_MONITOR.print(id);
                  SERIAL_PORT_MONITOR.print(",");

                  SERIAL_PORT_MONITOR.print(16 * buf[1] + buf[0], DEC);
                  SERIAL_PORT_MONITOR.print(",");
                  
                  SERIAL_PORT_MONITOR.print(16 * buf[3] + buf[2], DEC);
                  SERIAL_PORT_MONITOR.print(",");
                  
                  int A = 16 * buf[3] + buf[2];
                  int Temperature = A * Scale - Offset;
                  SERIAL_PORT_MONITOR.println();
                  
                  SERIAL_PORT_MONITOR.print(16 * buf[5] + buf[4], DEC);
                  SERIAL_PORT_MONITOR.println();

horace · April 20, 2022, 9:33am

any idea what device is the termperature sensor sending data via canbus?
any idea what was the original temperature which gave a readings of "9C 25"?

remay66 · April 20, 2022, 9:49am

To resume i have a Sparkfun Canbus Shield plug on a Arduino Mega and i have my sensor TR connected on the canbus shield.

Basically i just want to change my HEX data to Dec data to convert quickly.

GolamMostafa · April 20, 2022, 9:51am

0x259C ----> 27

Given below a Counting Method (Positional Factors are being multiplied by the corresponding Positional Weights) to convert the given hex number into decimal number.

byte myDigit[4];
int i = 0;

void setup()
{
  Serial.begin(9600);
  int y = 0x259C;
  do
  {
    myDigit[i] = y % 10;  //getting the decimal digits of the target decimal number: 8 2 6 9
    y = y / 10;
    i++;
  }
  while (y != 0);

  unsigned int myDec = myDigit[3] * 1000 + myDigit[2] * 100
                       + myDigit[1] * 10 + myDigit[0] * 1;
  myDec = (int)(myDec * 0.3125 - 273)/100;
  Serial.println(myDec);  //shows: 27
}

void loop() {}

sherzaad · April 20, 2022, 10:05am

something like this maybe...

void setup() {
  uint8_t sample_data[8] ={0x5D, 0xAF, 0x9C, 0x25, 0x64, 0x00, 0x64, 0x00};

  Serial.begin(115200);

  uint16_t temp_raw;
  memcpy(&temp_raw, &sample_data[2],2);

  Serial.print("0x");
  Serial.println(temp_raw,HEX);
  Serial.println(temp_raw,DEC);

  float temp_degC = ((temp_raw * 0.3125) - 273)/100;

  Serial.println(temp_degC,2);

}

void loop() {

  // put your main code here, to run repeatedly:

}

Output:

0x259C
9628
27.36

hope that helps...

GolamMostafa · April 20, 2022, 10:21am

An elegant approach (compared to % and / operation of post #8) who knows about the memcpy() function.

In school, the beginners like the % and / operation as the they face difficulties to understand the bureaucratic syntax of the memcpy() function.

void *memcpy(void *dest, const void * src, size_t n)

remay66 · April 20, 2022, 11:49am

uint8_t sample_data[8] ={0x5D, 0xAF, 0x9C, 0x25, 0x64, 0x00, 0x64, 0x00}; < this value updates all the time

This frame that I gave you is updated in real time in my monitor in the buf[i] ,
do you know if it is possible to replace buf[i] with your uint8_t sample_data[8] in your code?

And place your code in this loop of my code to have the concersion in decimal in real time :

for (int i = 0; i < len; i++) { // print the data
            SERIAL_PORT_MONITOR.print(buf[i], HEX);
            SERIAL_PORT_MONITOR.print("\t");
        }

thank you very much for your help ^^

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