CanBus v1.2 message delay and HEX structure

Hi everyone,

The past few weeks have gone really well using the canbus shield v1.2 for pulling a can dump from both my pontiac and my friends FRS. I was even able to broadcast RPM back to the pontiac and have it change the tach with the engine off.

Currently, I have the electronic steering system out of the FRS on a test bench in my living room, and need to broadcast (18) Can ID’s over the network. After a few weeks of recording and translating the Id’s from the car and rebroadcasting them, I haven’t had any success getting the test rig to respond.

I have 2 questions that I havn’t been able to find answers for:

  1. Can I just use CAN.sendMsgBuf one after another or do I need a delay after it? If I do use a delay, does it interfere with transmitting at the right times on the 500kbps bus?

  2. I am structuring the message “buff” for each ID as I recorded it, example :unsigned char msg152[8] = {0xF0, 0xE4, 0x0, 0x0, 0x0, 0x2, 0x0, 0x4C};.

    Should the buff be structured as I have it in HEX? or should I input decimal and the shield takes care of translating? My code is pasted below if anyone that might see something that I’m doing wrong. Thanks for the help.

// demo: CAN-BUS Shield, send data

#include <mcp_can.h>
#include <SPI.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 = 9;


unsigned char msg144[8] = {0xC0, 0x0, 0x71, 0x8A, 0x44, 0xA4, 0xA0, 0x0};// 0x140 70mph C0 0 71 8A 44 A4 A0 0
unsigned char msg360[8] = {0x96, 0x7, 0x87, 0x80, 0x37, 0x80, 0x1, 0x0};// 0x360 70mph: 96 7 87 80 37 80 1 0
unsigned char msg282[8] = {0xB0, 0xB1, 0x8A, 0x64, 0x64, 0x0, 0x20, 0x0};//282 70MPH : B0 B1 8A 64 64 0 20 0
unsigned char msg142[8] = {0x5B, 0x26, 0x8, 0x0, 0x0, 0x0, 0x0, 0x0};//0X142 70MPH 5B 26 8 0 0 0 0 0
unsigned char msg361[8] = {0x5, 0x29, 0x0, 0xD8, 0xD, 0xB0, 0x85, 0x79}; //5 29 0 D8 D B0 85 79
unsigned char msg152[8] = {0xF0, 0xE4, 0x0, 0x0, 0x0, 0x2, 0x0, 0x4C};
unsigned char msg372[8] = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0};// 0X372 0 0 0 0 0 0 0 0
unsigned char msg4DD[8] = {0x1E, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}; ///1E 0 0 0 0 0 0 0 (159661)
unsigned char msg4C1[8] = {0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0};//1 0 0 0 0 0 0 0
int dT = 0;//easy to change the delay between sending mesages

void setup() {

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");
Serial.println(“CAN BUS Shield init ok!”);
// Serial.println(msg18[2]);

void loop() {
CAN.sendMsgBuf(0x144, 0, 8, msg144); delay(dT);

CAN.sendMsgBuf(0x360, 0, 8, msg360); delay(dT);

CAN.sendMsgBuf(0x282, 0, 8, msg282); delay(dT);

CAN.sendMsgBuf(0x142, 0, 8, msg142); delay(dT);

CAN.sendMsgBuf(0x361, 0, 8, msg361); delay(dT);

CAN.sendMsgBuf(0x152, 0, 8, msg152); delay(dT);

CAN.sendMsgBuf(0x372, 0, 8, msg372); delay(dT);

CAN.sendMsgBuf(0x4DD, 0, 8, msg4DD); delay(dT);

CAN.sendMsgBuf(0x4C1, 0, 8, msg4C1); delay(dT);



1)In official examples, there is Delay(100) between each send, what frequency do you need to send? You can test it by yourself.

2)Arduino boards are not so smart, the compiler completes do this step if your decimal values are no more than 255. There are many tricks for assigning unsigned char arrays to variables of other data types, such as writing memory directly with pointers. If you are interested in it, you can study the relevant books of C and C++. But if you are not so good at coding, do it in the method you familiar with.