I2C: part 1

Introduction

In the previous Tutorial, we learned about Interrupt. In this tutorial we will learn about I2C communication.

I2C Communication

Inter-Integrated Circuit (I2C), is a two-wire communication protocol. This protocol is designed for short-distance communication between microcontrollers and peripherals. It uses two pins to set up the communication:

• SDA: Serial Data
• SCL: Serial Clock

This way of communication, allows us to connect more than 1 component to the same 2 pins. For I2C every component has its own address. These addresses are mostly 7-bit.

I2C is a master and slave protocol. It means that one device (Our Arduino) is a master, and the other devices are slaves. A master device controls the clock created in SCL. Also, master decides that if it wants to communicate with a slave or not. Each message of master is like below:

In the table above, you can see the message structure in I2C. First, master puts the SDA to low. This indicates that all slaves should listen. After that, it tells which slave address it wants to talk to. Then, with 1 bit tells the slave if it wants to read or write. Next, there would be an acknowledgement bit. If slave was available, it would set the acknowledgement bit to 0. (The default value of SDA is always 1). After that, there would be a byte of data. Respect to the mode (read or write), master can send or receive that byte. Then, whoever receives the data, should set the acknowledgement bit to 0. These byte transfer and acknowledgement can be repeated multiple times, until a stop signal. Stop signal can be created when we put the SDA to 1.

To have a I2C communication in Arduino uno, we should use these pins:

Wire

To control the I2C communication, Arduino has a library called Wire. We can include Wire in our code like below:

#include <Wire.h>

To set up the I2C communication, we can use .begin() function, like below:

Wire.begin();

After doing that, we can start a communication with a slave in two ways:

• write
• read

To start a communication with a slave in order to write, we can use the code below:

Wire.beginTransmission(addr);   // start the communication in order to write with the slave with the address of `addr`
Wire.write(data);               // write data
Wire.endTransmission();         // finish transmission

If we want to our communication to be a read communication, we can

Wire.requestFrom(addr, number); // start a read communication with the slave with the address of `addr` and read `number` bytes
Wire.read();                    // read bytes

Let’s connect an I2C component to the Arduino and check these functions.

Finding I2C address

• Connect the clock
• write the code
• Explain the code
• end transmission = 0

#include <Arduino.h>
#include <Wire.h>

void setup()
{
  Wire.begin();
  Serial.begin(9600);
}

void loop()
{
  for (int i = 0; i < 127; i++)
  {
    Wire.beginTransmission(i);
    if (Wire.endTransmission() == 0)
    {
      Serial.println("Device found at address: 0x" + String(i, HEX));
    }
  }
  delay(2000);
}

Clock: DS1307

• Storing: 0x22 -> 22 not 2*16+2
• seconds, minutes, hours, weekday, day, month, year
• SQW: Square Wave Output
  • Good for creating interrupts

Link to the Datasheet

OLED: SSD1306

lib_deps =
    Adafruit SSD1306
    Adafruit GFX Library

#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire);

if (!display.begin(SSD1306_SWITCHCAPVCC, SSD1306_ADDRESS))
{
Serial.println("SSD1306 failed!");
for (;;)
  ;
}

display.setTextSize(1);
display.setTextColor(WHITE, BLACK);

display.clearDisplay();
display.setCursor(0, 0);

display.print();
display.display();

Good Example

Project

Conclusion