Getting started with an IVT-S and Arduino Uno CAN bus shield

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First of all, set up your Arduino Uno and CAN bus shield.

Once the data is coming in over CAN, we can write a simple program to read the current value from the IVT-S.

There could be a lot of messages coming back on the CAN bus, so we specify a "mask" and "filter" for the CAN message IDs we are interested in. CAN bus message IDs are 11 bytes long, so we will specify a mask of 0x7ff (which is 11111111111 in binary). Using an MCP2515-based shield, we can set up to six different filter IDs. According to the Isabellenhütte IVT-S data sheet, the message ID of the "Current" reading from an IVT-S is 0x521, so we will specify that as the filter.

Testing current measurement with IVT-S
Testing current measurement with IVT-S

Once those parameters are set, the data should come in over CAN bus every 20ms at 1Mb/s.

Serial console output of measured current values on CAN bus
Serial console output of measured current values on CAN bus

The tricky part is that the current measurement comes from the the IVT-S as a buffer of four byte values in big endian order. We have to re-assemble these bytes to get the numerical current value (in mA). Once that's done, we get nice, readable numerical values on the serial console.

Here's the code:

// IVT-S meter using CAN bus shield
// electric_dart 2020

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

// the cs pin of the version after v1.1 is default to D9
// v0.9b and v1.0 is default D10
const int SPI_CS_PIN = 10;

MCP_CAN CAN(SPI_CS_PIN);                                    // Set CS pin

unsigned char len = 0;
unsigned char buf[8];

void setup() {
    // Set your Serial Monitor to 115200 baud

    // Initialise the CAN bus
    while (CAN_OK != CAN.begin(CAN_1000KBPS)) {            // init can bus
        Serial.println("Failed to initialise CAN bus. Retrying...");
    Serial.println("CAN bus initialised.");

        set receive mask
    CAN.init_Mask(0, 0, 0x7ff);                         // there are 2 masks in mcp2515, you need to set both of them
    CAN.init_Mask(1, 0, 0x7ff);                         // 0x7ff is '11111111111' in binary, so we are checking 11 of the CAN message ID bits  

        set receive filter
    CAN.init_Filt(0, 0, 0x521);                          // there are 6 filters in mcp2515
    CAN.init_Filt(1, 0, 0x521);                          // 0x521 is the CAN message ID for IVT-S Current value
    CAN.init_Filt(2, 0, 0x521);                          
    CAN.init_Filt(3, 0, 0x521);                          
    CAN.init_Filt(4, 0, 0x521);                          
    CAN.init_Filt(5, 0, 0x521);                          


void loop() {
    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();

        if (canId == 0x521) {
          Serial.print("Data received from IVT_Msg_Result_I");
          // Convert individual big endian byte values to actual reading 
          long reading = (buf[2] << 24) | (buf[3] << 16) | (buf[4] << 8) | (buf[5]);
    // Refresh every 250ms