Connecting two Arduinos. Master / Slave....

Using Arduino Programming Questions
1

I found a video on youtube, copied and edited it. So that the code light the led (slave) from a push button (master), rather than a PC keyboard.

I was wondering if there is a simple way to it... Rather than sending H or L. I would like to send something like "Button1"

I dont really understand the char c = Wire.read();
and why I can only send one letter... If I change it to a word, it doesn't work.

Master

//i2c Master Code(Mega 2560)
#include <Wire.h>
const int buttonPin = 2;
int buttonState = 0;

void setup()
{
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
  Wire.begin();
}

void loop()
{
 
  buttonState = digitalRead(buttonPin);
  
  if (buttonState == HIGH) {
      Wire.beginTransmission(5);
      Wire.write('H');
      Wire.endTransmission();
    }
    
  else {
      Wire.beginTransmission(5);
      Wire.write('L');
      Wire.endTransmission();
   
  }
}

Slave

//i2c Slave Code(Uno)
#include <Wire.h>

void setup()
{
  Wire.begin(5);
  Wire.onReceive(receiveEvent);
  
  pinMode(13,OUTPUT);
  digitalWrite(13,LOW);
}

void loop()
{
}

void receiveEvent(int howMany)
{
  while(Wire.available())
  {
    char c = Wire.read();
    
    if(c == 'H')
    {
      digitalWrite(13,HIGH);
    }
    else if(c == 'L')
    {
      digitalWrite(13,LOW);
    }
  }
}

Any help would be great.

Thanks.

2

Have you done much reading at the Wire.h library page?
I2C only sends one byte at a time. If you want longer, you need to read the bytes and put them together into something longer, than act on longer thing.

3

Reading now. Thank you.

4

If you can convey all the information you need in a single character (and it seems like you can) then it is pointless to make the code more complex just to send additional superfluous characters.

A guy called Claude Shannon made a name for himself out of "less is more".

...R

5

I still dont understand the

char c = Wire.read();

Is the c a real thing? Or are the using c as a random char?

6

Hi,
Take a look at some of the different RFID program loops, they might help you understand how to receive and send code from one device to another.

Basically you send a starting tag and a complete tag so that your second system knows when the first system is done sending.

Yes you can do it with one char and then do a switch case for the actions that you want performed based on the char sent

Hope it helps

Jasit

7

"c" in this case is just a variable name. "incomingByte" could have been as easily used.