Article #20 : Using interrupts with Arduino Uno

Introduction :

An interruption, as its name indicates, interrupts momentarily the program executed by Arduino to perform another task. When the task finishes, the program takes on the lead from the axact place where it was interrupted.

Interruptions could be ideally used for listening to user’s actions, for example pressing a button, a keypad, or the changing state of a sensor without the need of constantly reading a pin’s state.

How does it work ?

Arduino Uno (ATMega328) can manage 2 external interruptions on its pins INT0 and INT1 mapped to pins D2 and D3 on the microcontroller board.

Interruptions could be triggered under 4 modes :

•             LOW : The pin is in a low state
•             RISING : The pin passes from low to high state
•             FALLING : The pin passes from high to low state
•             CHANGE : The pin has changed state

Creating an interrupt :

To “listen” for an interruption on Arduino, you only have to attach an interrupt on either pin D2 or D3 using the method attachInterrupt. This method takes as an argument the interruption’s pin number 0 or 1, the name of the function called by the interruption, and finally the interruption mode as the following example shows :

attachInterrupt(0, myInterrupt(), RISING);

Even though Arduino’s pin is D2, we indicate 0 for the interruption’s pin (0 for INT0 / D2, 1 for INT1 / D3).

The function attached to the interrupt have to take a small amout of time to execute and it is also forbidden to use time based instructions in the interior of the function as it blocks the microcontroller.

Application :

In the following application, we attach an interruption to a push button. The program writes the interruption number to the serial monitor every time the button is pushed.

Code :

int interruption = 0; //interrupt 0 is on digital pin 2
volatile int numInterrupt = 0; //variables used inside interrupt     functions declared as volatile

void setup() {

       Serial.begin(9600);
       attachInterrupt(interruption, functionInterruption, FALLING);

}

Void loop() {

//simulating a task being executed repeatedly
            While(true) {
                        Serial.print(“.”);
                        delay(250);

}
}

Void functionInterruption() {

            Serial.print(“Interrupt numero ”);
            Serial.println(numInterrupt);
            numInterrupt++;


}

Article #19 : Arduino Timers

Introduction :

When we start learning about microcontrollers, and especially Arduino in our case, the first program that you have written was most probably the famous blinking LED program. In that program you certainly used to call the delay() function to set the time interval between blinks. The only thing is that delay() sets Arduino on pause mode, so how we can blink the LED while still using Arduino for doing other tasks at the same time like sending serial data for example ? That’s why we are going to learn about the Timer library to facilitate this task. 

The library :

The library Timer has a simple functioning principle. After adding the library to our project, we can create a variable of type Timer, then we update it in the loop function and finally give some instructions to our timer to perform the tasks like blinking an LED for 100ms for example.

Basic Commands :

As said previously, we have to import the Timer library to our program.

#include “Timer”

Then, we have to create our variable of type timer :

Timer timer;

Also, we have to update our newly created timer in the loop function as follows :

void loop(){

Timer.update();

}

Now we don’t need to use the delay() function anymore. We have our timer to count time in the program.

The most used functions in the Timer library are the following :

int every(long period, callback, int repeatCount)

Run the 'callback' every 'period' milliseconds for a total of 'repeatCount' times.

int after(long duration, callback)

Run the 'callback' once after 'period' milliseconds.

int oscillate(int pin, long period, int startingValue, int repeatCount)

Toggle the state of the digital output 'pin' every 'period' milliseconds 'repeatCount' times. 

The pin's starting value is specified in 'startingValue', which should be HIGH or LOW.

int pulse(int pin, long period, int startingValue)

Toggle the state of the digital output 'pin' just once after 'period' milliseconds. 

The pin's starting value is specified in 'startingValue', which should be HIGH or LOW.

int update()

Must be called from 'loop'. This will service all the events associated with the timer.

Examples :

The following example is a program that passes a pin from a state to another for a set period of time only once. To do it we need to implement the ‘pulse’ method.

#include "Timer.h"

Timer t;

int pin = 13; 

void setup()

{

  pinMode(pin, OUTPUT);

  t.pulse(pin, 10 * 60 * 1000, HIGH); // 10 minutes  

}

void loop()

{

  t.update();

}

The update method in the loop function takes only few milliseconds to run, and the program can continue executing other instructions while the timer counts the time in the setup function.

The second example is program that toggles the pin 13 from a state to another every 100 ms and reads the analog pin 0 from the serial monitor every 2 seconds.

#include "Timer.h"

Timer t;

int pin = 13;

void setup()

{

  Serial.begin(9600);

  pinMode(pin, OUTPUT);

  t.oscillate(pin, 100, LOW); // la fonction qui fait clignoter la led toutes les 100 ms

  t.every(1000, envoi); // et celle-ci qui appelle la fonction 'envoi' toutes les secondes

} 

void loop()

{

  t.update();

} 

void envoi() // fonction qui envoie par liaison série l'entrée du pin 0

{

  Serial.println(analogRead(0));

}

References :

http://playground.arduino.cc/Code/Timer

Article #18 : Using Arduino To Program an SD Card

Introduction :

Arduino offers the possibility to read from and write to SD cards using the Sd library. However, because the Arduino board doesn’t have a built-in SD card input you have to connect a shield that have an SD card reader into your board. After that, you will be able to use it for a multitude of applications such as reading sensor data values and storing them into the SD card.

In this tutorial, we will see how to connect the SD card shield to the microcontroller, write some basic commands of the SD library and finally write a program creating a file, writing data into it and reading it after.

Project parts :

•         Arduino Uno.
•           SD card shield.

SD card shield pinout :

First, you need to connect the shield to the Arduino board. On every pin of the shield, there is a label. S, you have to connect avery pin of the shield (+5v, GND, SCK, MOSI, MISO) to its corresponding pin on the Arduino card, according to the documentation of Arduino Uno :

•        MOSI è Pin 11
•        MISO è Pin 12
•        SCK   è Pin 13
•        SS      è Pin 10

Then, connect the Cs pin on any of the remaining digital I/O pins of your Arduino, in this tutorial, I have connected it to pin 5.

You also have to format the SD card to FAT16 or FAT32 from your computer.

Basic Codes :

As always, you have to include the library

#include <SD.h>

To create a file you have to create a variable of type File.

File file;

Then, in the setup function, you have to write a code to start the SD card. The following sequence of code enables to determine if there is a connection error via the serial bus.

If(!SD.begin(5)) {

          Serial.println(“Starting SD card error!”);

}

Serial.println(“SD card ready.”);

Using the File variable that we have created, we can open the file in read or write mode.

file = SD.open(“myFile.txt”, FILE_WRITE);//file on writing mode

file = SD.open(“myFile.txt”, FILE_READ);//file on read mode

We usually have to check if the file has been opened, for that we use the following condition :

if (file) {

          Serial.print(“File opened successfully”);

}else {

          Serial.println(“error while opening the file”);

}

We can then write to or read from the created file depending on the defined mode.

file.println(“Welcome to simple-arduino tutorial !”);

file.close();//always remember to close the file after

In read mode, we create a loop that reads the file until its end.

While(file.available()) {

          char c = file.read();

          Serial.write(c);//send the character to serial monitor

}

Total Code:

The following code uses all functions that we have seen above. It writes to a file, then sends the data over serial bus to the screen.

#include <SD.write>

File file;

void setup() {

          Serial.begin(9600);

          Serial.print(“Initializing SD card”);

          pinMode(10, OUTPUT);

         if (!SD.begin(5)) {

                   Serial.println("initialization failed!");

                   return;

         }

         Serial.println("initialization done.");

         file = SD.open("test.txt", FILE_WRITE);

// if the file opened okay, write to it:

  if (myFile) {

    Serial.print("Writing to test.txt...");

    myFile.println("testing 1, 2, 3.");

    // close the file:

    myFile.close();

    Serial.println("done.");

  } else {

    // if the file didn't open, print an error:

    Serial.println("error opening test.txt");

  }

 

  // re-open the file for reading:

  myFile = SD.open("test.txt");

  if (myFile) {

    Serial.println("test.txt:");

   

    // read from the file until there's nothing else in it:

    while (myFile.available()) {

        Serial.write(myFile.read());

    }

    // close the file:

    myFile.close();

  } else {

    // if the file didn't open, print an error:

    Serial.println("error opening test.txt");

  }

}

void loop()

{

    // all programming happens in setup mode

}

ARTICLE #17 : Using Arduino with Processing

Introduction :

For writing programs and loading them to the Arduino board, we used the Arduino IDE program. Now we will see another programming language and IDE to communicate with Arduino using serial port which is called Processing.

Processing is simply an open source computer programming language and IDE built for the electronic arts using a visual context. The processing language is based on the Java language. So the programs that we are going to write are similar to Java code.

In this tutorial we will see :

•         How to send data from Android and receive it in Processing.
•         How to send data from processing and receive it in Android.

To perform this tutorial you will have to have:

•         Arduino IDE download it from here.
•         Processing IDE download it from here.

Hello world :

We will write a “hello world” to the Arduino board using Arduino IDE and then manage to receive it in the Processing IDE.

Code Arduino :

Void setup() {

            Serial.begin(9600); //initializing serial communications

}

Void loop() {

            Serial.println(“hello world”); //wait 500 ms and write it again

}

Code Processing :

To receive data in Processing we have to create an object from serial class that will get the communication port that Arduino is hooked to.

import processing.serial.*;

Serial myPort;

String val; //Data received from the serial port

void setup() {

            String portName = Serial.list()[0];//depending on the port number of the device

            myPort = new Serial(this, portName, 9600);

}

void draw() {

            if(myPort.available() > 0) { //If data is available

                        val = myPort.readStringUntil(‘\n’);//read the string and put it in val

                        If(val != null)

                                    Println(val);

            }

}

Now that we learned how to receive data sent from Arduino to Processing. We will now learn how to do it the other way, from processing to Arduino.

What does the following code ? whenever we press the mouse, processing sends ‘1’ to Arduino. Whenever the Arduino IDE catches ‘1’ it turns the LED pin 13 on.

Code Processing :

import processing.serial.*;

Serial myPort; //Creating a Serial object

void setup() {

            size(200, 200);//The space for the mouse to click

            String portName = Serial.list()[0];

            myPort = new Serial(this, portName, 9600);

}

void draw() {

            if(mousePresses == true) {

                        myPort.write(‘1’);//send 1 over the serial port

                        println(“1”);//printing it to make sure we are sending 1

                        } else {

                        myPort.write(‘0’); //send 0 instead

                        }

}

Code Arduino :

char cal;

int ledPin = 13;

void setup() {

            pinMode(ledPin, OUTPUT);

            Serial.begin(9600);

}

void loop() {

            if(Serial.available()) {

                        val = Serial.read();

            }

if (val == ‘1’) {

            digitalWrite(ledPin, HIGH);

            } else {

            digitalWrite(ledPin, LOW);

}

delay(10);

}

When we load the code above to Arduino and run Processing sketch, you should be able to turn the LED on by simply clicking into the created processing canvas.