Seeed CAN Shield & Uno R3 w/ Haltech ECU

Projects Networking, Protocols, and Devices
1

Hello everyone,

I'm trying to use a Seeed CAN Shield and Arduino Uno to create an LCD gauge. I'm not having any issues connecting to the ECU, (Haltech Pro-Plugin), and using the examples provided with the libraries. I can see the CAN ID and buffer information in the serial screen just fine.

Using the provided sample code, (and switching to 1000Kbps):

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


const int SPI_CS_PIN = 9;

MCP_CAN CAN(SPI_CS_PIN);                                    

void setup()
{
    Serial.begin(115200);

    while (CAN_OK != CAN.begin(CAN_1000KBPS))              // Haltech uses 1,000Kbps
    {
        Serial.println("CAN BUS Failure...");
        delay(100);
    }
    Serial.println("CAN BUS is ready!");
}


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

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

        unsigned char canId = CAN.getCanId();
        
        Serial.println("-----------------------------");
        Serial.print("CAN ID: ");
        Serial.println(canId, HEX);

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

I receive clear and accurate CAN information from the ECU:

CAN ID: 68
3 AC 0 0 0 0 0 0 
-----------------------------
CAN ID: 6F
0 0 0 0 0 0 0 0 
-----------------------------
CAN ID: 75
0 0 0 0 0 0 0 0 
-----------------------------
CAN ID: 60
5 8 1 7F 0 0 0 0

What I'm having trouble with, is pulling out pieces of the buffer to convert and display on the serial screen, or an LCD screen. ID 68 shows 8 bytes in the buffer, 0 & 1 being lambda(air-fuel ratio) information. The remaining bytes are not used, as those would be for additional wideband sensors. Bytes 0 & 1 combine to hexadecimal 3AC, or decimal 940. I should be able to convert these values further on my own, (940 x .001 = .940 lambda = 13.82 AFR).

I'm having a difficult time pulling these values out directly to display a simple AFR reading on an LCD screen, or the serial screen at least.

Does anyone have any recommendations?
I appreciate any and all help. I've been at this for a few days with no luck. I won't bother showing my botched attempts as there's quite a few, and they're embarrassing.

Thank you

2

I apologize for posting in the wrong section. I realize this should probably be in Programming Questions.

3

Hi StrokerSi,

What you need to do is to have some type conversions. For the example you mentioned, the ID 86 has the data buffer as:

3 AC 0 0 0 0 0 0

or you also could say:

buf[0] = 0x03
buf[1] = 0xAC
buf[2] = 0x00
(...)

I'n not familiar with the data but if as far I understoo you just need to "merge" those two "uint8_t" bytes into a single "uint16_t" variable. To do that, just use some bit operations, like left or right shifting:

if (canId == 0x68)
{
  uint16_t reading = 0;
  reading = (uint16_t)buf[0] << 8;
  reading |= buf[1];

  Serial.println(reading);
}

I don't have a C compiler here to test the code, but I believe the idea is quite clear how you can convert two uint8_t into a uint16_t. There a few example on the internet (like this one: c - Combining two uint8_t as uint16_t - Stack Overflow). Also, there are many ways to write the same thing, you can do all in a single line or break in multiple lines, depending on your preference.

I also recommend you to stay away from "float" numbers as much as you can, and only "convert" it when you're printing.

4

musskopf:
I'n not familiar with the data but if as far I understoo you just need to "merge" those two "uint8_t" bytes into a single "uint16_t" variable. To do that, just use some bit operations, like left or right shifting:

if (canId == 0x68)

{
  uint16_t reading = 0;
  reading = (uint16_t)buf[0] << 8;
  reading |= buf[1];

Serial.println(reading);
}

I see what you're getting at. I'll give it a shot in the morning.

Sort of a pain that I have to hook it up to the car each time I make a change.

Much appreciated!

5

You already have some data samples, so you don't need to hook back in the car to try things out. Just "simulate" the data buffer and go from there.

Cheers