Your first Arduino program

So you’ve been hearing about this Arduino thing and you made the jump and downloaded the IDE since it’s a good first step and doesn’t cost anything. Now what?

Well, first of all, what’s an “IDE?” An IDE is an abbreviation for Integrated Development Environment. To write code you need a text editor and to program the Arduino device, you need a programmer. The “I” in Integrated means that the application contains both an editor and a programmer. The Arduino IDE is a very basic one but it gets the job done.

So, what’s a “sketch?” A sketch is the Arduino terminology for a computer program, which is the set of instructions you give a computer to tell it to do something. We also call this “code.” Why the Arduino inventors called a program a sketch I have no idea, but it seems to have stuck.

void setup()
{
}

The lines above are familiar to anyone who’s written an Arduino sketch. The basic outline of a sketch has two of these blocks called “functions.” A function is a short block of code that can be called, or told to execute from anywhere in your program. The other basic function is “loop” and we’ll get to it later. For now, the important thing to know is that setup is called when the program starts and loop is called repeatedly, over and over.

Since setup is called at the beginning, it’s the place where we put statements that need to be executed as soon as the Arduino starts up. e.g., we need to tell it which pins we want to use as inputs and outputs, what special configurations they need, and so on. Here’s a basic program that makes pins 2&3 outputs and blinks them five times.

void setup(void)
{
    // Set pins 2 and 3 as outputs
    pinMode(2, OUTPUT);
    pinMode(3, OUTPUT);

    // Declare a variable for counting
    int i = 0;
    // Turn pins 2 & 3 off 5 times
    // using a for... loop
    for( i = 0; i < 5; i++ )
    {
        // Turn OFF pin 2
        digitalWrite(2, LOW);
        // Turn ON pin 3
        digitalWrite(3, HIGH);
        // Pause for 1000 milliseconds (1 second)
        delay(1000);

        // Turn ON pin 2
        digitalWrite(2, HIGH);
        // Turn OFF pin 3
        digitalWrite(3, LOW);
        // Pause for 1000 milliseconds (1 second)
        delay(1000);
    }
    // Turn OFF pin 2
    digitalWrite(2, LOW);
}

The short block of code above shows something important that’s often ignored: you can do real work in the setup() function. In fact, for some very short programs that just need to do a task and stop, it’s a good way to write your code.

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