please help with a simple code / Send CAN-BUS message with button press

flopyro · February 10, 2020, 7:41am

hello,
i'm a total beginner when it comes to Code.
can you please help me out? I want to send a CAN Message when i press a physical button.
how do i code this ? i thik it should be something like:

#include <SPI.h>

#include <mcp2515.h>


struct can_frame canMsg1;
struct can_frame canMsg2;
MCP2515 mcp2515(10);


const int buttonPin = 2;
int buttonState = 0;


void setup() {

 

  canMsg1.can_id  = 0x111;
  canMsg1.can_dlc = 8;
  canMsg1.data[0] = 0x8E;
  canMsg1.data[1] = 0x87;
  canMsg1.data[2] = 0x32;
  canMsg1.data[3] = 0xFA;
  canMsg1.data[4] = 0x26;
  canMsg1.data[5] = 0x8E;
  canMsg1.data[6] = 0xBE;
  canMsg1.data[7] = 0x86;


 
  canMsg2.can_id  = 0x222;
  canMsg2.can_dlc = 8;
  canMsg2.data[0] = 0x0E;
  canMsg2.data[1] = 0x00;
  canMsg2.data[2] = 0x00;
  canMsg2.data[3] = 0x08;
  canMsg2.data[4] = 0x01;
  canMsg2.data[5] = 0x00;
  canMsg2.data[6] = 0x00;
  canMsg2.data[7] = 0xA0;


 
  while (!Serial);
  Serial.begin(115200);
  SPI.begin();

 
mcp2515.reset();
  mcp2515.setBitrate(CAN_500KBPS,MCP_8MHZ);
  mcp2515.setNormalMode();


pinMode(buttonPin, INPUT);
  pinMode(ledPin, OUTPUT);

 
}


void loop() {

  buttonState = digitalRead(buttonPin);  // read the state of the pushbutton value
  Serial.println(buttonState); // Show the state of pushbutton on serial monitor

  if (buttonState == HIGH) {      // check if the pushbutton is pressed.
   
// CAN message1 send:
    digitalWrite(mcp2515.sendMessage(&canMsg1));
  }

 
  Serial.println("Messages (&canMsg1) sent");

 
  delay(100);

}

could please someone correct the code ?
thank you !

UKHeliBob · February 10, 2020, 7:50am

What is the problem ?

How is the input pin wired ?
Does it have a pulldown resistor or is it floating at an unknown voltage ?

flopyro · February 12, 2020, 5:19pm

UKHeliBob:
What is the problem ?

How is the input pin wired ?
Does it have a pulldown resistor or is it floating at an unknown voltage ?

Hello UKHeliBob,
the button has a pulldown resistor.

ok , i have conencted the Button now to PIN 3 (Arduino D3)
and i have adjusted the code like this:

#include <SPI.h>
#include <mcp2515.h>

struct can_frame canMsg1;
struct can_frame canMsg2;
MCP2515 mcp2515(10);
const int buttonPin = 3;
int buttonState = 0;

void setup() {

  canMsg1.can_id  = 0x111;
  canMsg1.can_dlc = 8;
  canMsg1.data[0] = 0x8E;
  canMsg1.data[1] = 0x87;
  canMsg1.data[2] = 0x32;
  canMsg1.data[3] = 0xFA;
  canMsg1.data[4] = 0x26;
  canMsg1.data[5] = 0x8E;
  canMsg1.data[6] = 0xBE;
  canMsg1.data[7] = 0x86;
 
  canMsg2.can_id  = 0x222;
  canMsg2.can_dlc = 8;
  canMsg2.data[0] = 0x0E;
  canMsg2.data[1] = 0x00;
  canMsg2.data[2] = 0x00;
  canMsg2.data[3] = 0x08;
  canMsg2.data[4] = 0x01;
  canMsg2.data[5] = 0x00;
  canMsg2.data[6] = 0x00;
  canMsg2.data[7] = 0xA0;

  while (!Serial);
  Serial.begin(115200);
  SPI.begin();
 
mcp2515.reset();
  mcp2515.setBitrate(CAN_500KBPS,MCP_8MHZ);
  mcp2515.setNormalMode();

pinMode(buttonPin, INPUT);
}

void loop() {

  buttonState = digitalRead(buttonPin);  // read the state of the pushbutton value
  Serial.println(buttonState); // Show the state of pushbutton on serial monitor
  if (buttonState == HIGH) 
  
  {      // check if the pushbutton is pressed.
  // CAN message1 send:
    digitalWrite(mcp2515.sendMessage(&canMsg1), HIGH); }

else {
    // CAN message1 not send:
    digitalWrite(mcp2515.sendMessage(&canMsg2), LOW);
  }


  delay(100);
}

But like this the Message 2 gets sent all the time, and only when i push the button the Message 1 gets send.
This is not the behaviour that i wanted.
Attached screenshot with the behaviour

I want to send the Message 1, ONLY when i push the button. not to send the message 2 all the time, and message 1 by pushing the button.
how do i stop it from sending messages ?

UKHeliBob · February 12, 2020, 5:53pm

digitalWrite(mcp2515.sendMessage(&canMsg1), HIGH);
What does the sendMessage() function return ?
Which pin do you want to go HIGH, bearing in ind that you have no pins defined as outputs ?

Where did you get the mcp2515 library ?

flopyro · February 14, 2020, 3:33pm

UKHeliBob:
digitalWrite(mcp2515.sendMessage(&canMsg1), HIGH);
What does the sendMessage() function return ?
Which pin do you want to go HIGH, bearing in ind that you have no pins defined as outputs ?

Where did you get the mcp2515 library ?

the mcp2515 library i got from here: GitHub - autowp/arduino-mcp2515: Arduino MCP2515 CAN interface library (https://github.com/autowp/arduino-mcp2515/archive/master.zip)
and the function sendMessage() sends the can message that i set in the code, like in the previous attached file
Which pin do you want to go HIGH, bearing in ind that you have no pins defined as outputs ? --> i don't want any pin to go to high, i just want to send the can message, but i don't know how to do it else

Thank you

UKHeliBob · February 14, 2020, 3:44pm

digitalWrite(mcp2515.sendMessage(&canMsg1), HIGH);

Let's break down this function call :

digitalWrite() takes 2 parameters. The first is the pin number to write to and the second is the state to set the pin to. So, if you wrote digitalWrite(3, HIGH), for instance, pin 3 would be set HIGH. In your code you have not got an explicit pin number, rather you have the value returned from the call to the mcp2515.sendMessage() function, hence my question

Now, if you don't want a pin to go HIGH why are you using digitalWrite() ?

It looks to me as though you should use

mcp2515.sendMessage(&canMsg1)

which is what is used in the examples

flopyro · February 16, 2020, 6:44pm

ok ok, you are right, it worked.
i adjusted the code like you told me:

#include <SPI.h>
#include <mcp2515.h>

struct can_frame canMsg1;
struct can_frame canMsg2;
MCP2515 mcp2515(10);
const int buttonPin = 3;
int buttonState = 0;

void setup() {

  canMsg1.can_id  = 0x111;
  canMsg1.can_dlc = 8;
  canMsg1.data[0] = 0x8E;
  canMsg1.data[1] = 0x87;
  canMsg1.data[2] = 0x32;
  canMsg1.data[3] = 0xFA;
  canMsg1.data[4] = 0x26;
  canMsg1.data[5] = 0x8E;
  canMsg1.data[6] = 0xBE;
  canMsg1.data[7] = 0x86;
 
  canMsg2.can_id  = 0x222;
  canMsg2.can_dlc = 8;
  canMsg2.data[0] = 0x0E;
  canMsg2.data[1] = 0x00;
  canMsg2.data[2] = 0x00;
  canMsg2.data[3] = 0x08;
  canMsg2.data[4] = 0x01;
  canMsg2.data[5] = 0x00;
  canMsg2.data[6] = 0x00;
  canMsg2.data[7] = 0xA0;

  while (!Serial);
  Serial.begin(115200);
  SPI.begin();
 
mcp2515.reset();
  mcp2515.setBitrate(CAN_500KBPS,MCP_8MHZ);
  mcp2515.setNormalMode();

pinMode(buttonPin, INPUT);
}

void loop() {

  buttonState = digitalRead(buttonPin);  // read the state of the pushbutton value
  Serial.println(buttonState); // Show the state of pushbutton on serial monitor
  if (buttonState == HIGH) 
  
  {      // check if the pushbutton is pressed.
  // CAN message1 send:
    mcp2515.sendMessage(&canMsg1); }




  delay(100);
}

and it really sends the can message ONLY when i push the button (screen shot in attachment).
now i have to see how to make it more reliable (the detection of the pushed button more accurate) i saw somwhere that i should put a delay between reading out the button and executing the function or somthing like that and afterwards it should be better ....or ?

again...maybe a hint how could i do it better ?

anyways, THANK YOU !!!
thank you for your time !

UKHeliBob · February 16, 2020, 6:49pm

If I were you I would consider sending the message when the button becomes pressed rather than when it is pressed. See the StateChangeDetection example in the IDE and research debouncing of inputs

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please help with a simple code / Send CAN-BUS message with button press

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