Blink using Arduino

Introduction

OK you’ve gotten yourArduino set up and also figured out how to use the software to send sketches tothe board. Next step is to start writing your own sketches. We’ll start offeasy by just modifying something that already works.

To start we will venturedeep into the Blink sketch, looking at each line and trying to understand whatits doing.

Then we will starthacking the sketch!

Blinkie

The sketch itself is inthe text input area of the Arduino software. Sketches are written in text, justlike a document. When you select Compile/Verifyfrom the menu, the Arduino software looks over the document andtranslates it to Arduino-machine-language – which is not human-readable but iseasy for the Arduino to understand.

Sketches themselves arewritten in C, which is a programming language that is very popular andpowerful. It takes a bit of getting used to but we will go through theseexamples slowly.

/*

 * Blink

 *

 * Thebasic Arduino example.  Turns on an LEDon for one second,

 * thenoff for one second, and so on…  We usepin 13 because,

 *depending on your Arduino board, it has either a built-in LED

 * or abuilt-in resistor so that you need only an LED.

 *

 *http://www.arduino.cc/en/Tutorial/Blink

 */

intledPin = 13;                // LED connected todigital pin 13

voidsetup()                    // run once, when thesketch starts

{

  pinMode(ledPin, OUTPUT);      // sets the digital pin as output

}

voidloop()                     // run over and overagain

{

  digitalWrite(ledPin, HIGH);   // sets the LED on

  delay(1000);                  // waits for a second

  digitalWrite(ledPin, LOW);    // sets the LED off

  delay(1000);                  // waits for a second

}

Comments

Lets examine this sketchin detail starting with the first section:

/*

 * Blink

 *

 * Thebasic Arduino example.  Turns on an LEDon for one second,

 * thenoff for one second, and so on…  We usepin 13 because,

 *depending on your Arduino board, it has either a built-in LED

 * or abuilt-in resistor so that you need only an LED.

 *

 *http://www.arduino.cc/en/Tutorial/Blink

 */

This is a comment, it is text that is not used by the Arduino,its only there to help humans like us understand whats going on. You can tellif something is a comment because there is a /* at the beginning and a */ at the end. Anything between the /* and */ isignored by the Arduino. In this example the person who wrote the commentdecided to make it look pretty and add *’s down the side but this isn’tnecessary.
Comments are very useful and I strongly encourage every sketch you make have acomment in the beginning with information like who wrote it, when you wrote itand what its supposed to do.

Variables

Lets look at the nextline:

intledPin = 13;                // LED connected todigital pin 13

This is the first lineof actual instruction code. It is also extremely unlike English (or any otherhuman language). The first part we can easily understand is the part to theright, which is also a comment. Turns out if you want to make a small comment,you can use // as well as /* */. // is often used for short, one line comments.

The rest of the line,the stuff before the //, is what is called a statement, which is basically like a computerizedsentence. Much like human sentances end with a . (period), all computersentences end with a ; (semicolon)

OK all we have left isthe statement itself, which turns out to be a sentence telling the computerthat we would like it to create a box named ledPin and to put the number 13 in that box. If youremember your math, you may recall that the box is also known as variable.

box-type	box-name	=	stuff-to-put-in-box
int	ledPin	=	13

The first part of thissentence is int, whichis short for integer which is a fancy way of saying whole number 

The second part of this sentence is ledPin which is the name of the box
The third part is an =, which basically says that the variable (box) namedledPin should start out equaling whatever is after the =
The fourth part is 13, a whole number (integer) which is assigned to ledPin

Procedures

Lets move on to the nextsection 

voidsetup()                    // run once, when thesketch starts

{

  pinMode(ledPin, OUTPUT);      // sets the digital pin as output

}

OK we’ve got twocomments, each starting with //. We understand comments already so lets skipthat.
We also see in the middle there is a statement, we know its a statement becauseit ends with a ; (semicolon) however there’s a whole bunch more stuff before andafter it.
This bunch of code is an example of a procedure, a procedure is a collection of statements, itsused to group statements together so that we can refer to them all with onename. Its just like a procedure that we use to perform a task step by step.

returned value	procedure name	(input values)	{ statements }
void	setup	()	{ pinMode(ledPin, OUTPUT); }

To better understandprocedures, lets use an analogy to the kinds of procedures we’re used to

clean catwash thecat(dirty cat)                    // a procedure forwashing the cat

{

        turn on the shower.

        find the cat.

        grab the cat.

        put cat under shower.

        wait 3 minutes.                                     // wait for cat to get clean.

        release cat.

}

This is a procedure forwashing the cat. The name of the procedure is wash the cat, it uses a dirty cat as the input and returns a clean cat upon success. There are two brackets, an openbracket { and a closed bracket }, thats are used to indicate the beginning andend of the procedure. Inside the procedure are a bunch of statements,indicating the correct procedure for washing a cat. If you perform all of thestatements then you should be able to turn a dirty cat into a clean cat.

Looking again at theprocedure, we see that it is named setup and it has no input values and it returns void. Now you’re probably asking yourself “whatisvoid?” Well thats a computer-scientist way ofsaying nothing. That is, this procedure doesnt returnanything. (That doesnt mean it doesn’t do anything, just that it doesn’t have atangible number or whatever, to show when its complete)

voidsetup()                    // run once, when thesketch starts

There is one statment inthis procedure,

pinMode(ledPin,OUTPUT);      // sets the digital pinas output

We’ll return to thisstatement in detail later, suffice to say it is a way of telling the Arduinowhat we would like to do with one of the physical pins on the main processorchip.

Procedure calls

We’re onto the nextbunch of text.

voidloop()                     // run over and overagain

{

  digitalWrite(ledPin, HIGH);   // sets the LED on

  delay(1000);                  // waits for a second

  digitalWrite(ledPin, LOW);    // sets the LED off

  delay(1000);                  // waits for a second

}

Using our now well-honedtechnique we recognize that the text to the right is all comments. We alsorecognize another procedure, this one called loopwhich also has no inputs or output. This procedure has multiplestatements, one after the other.

We’re going to skip thefirst statement for now and go straight to statement #2.

The second and fourthstatements are the same, and have something to do with a delay. This statement is very similar to the”wait 3 minutes.” command in our cat-washing procedure. Thisstatement says “Dear Arduino. Stop what you’re doing for a short amount oftime. Thanks!” 
To do this, the statement performs a procedure call. (We will use the phrasing calls aprocedure). Basically, we wantthe Arduino to take a break but don’t quite know how to do it, lucky for us,someone else wrote a procedure called delay which we can call upon to do the work for us. Kind of like if we needto do our taxes and we dont know how, we call upon an accountant to do it forus, giving them the paperwork input and getting tax return as the result.

procedure name	(input values)	;
delay	(1000)	;

This means thatsomewhere out there, there’s a procedure something like this: 

voiddelay(numberof milliseconds) 

{

  “Dear Arduino. Stopwhat you’re doing for (number of milliseconds)amount of time. Thanks!”

}

(Of course, this exampleis not proper code)

Turns out this delay procedure works pretty well, and all we have todo is tell it how many milliseconds (1/1000th of a second) to wait and it willdo the job for us.

Returning to the firststatment, we see that it is also a procedure call. This time for some procedurecalled digitalWrite. We’ll also skip this one in detail for a bit,except to explain that its turning a pin on the Arduino chip on and off, andthat pin is powering the LED so in essence its turning the LED on and off.

Special Procedures -Setup() and Loop()

I do want to mentionquickly here that the two procedures we’ve mentioned so far are extra-specialin that when the Arduino first wakes up after being reset, it always does whatsin the setup procedure first. Then it does whatever is in the loop procedure over and over and over…forever! Orat least until you turn it off.

Modifying the example

Now that we’ve analyzedthe entire program it’s time to make some changes. In your Arduino software,change the number in the delay procedure calls to 500 (from 1000) as shown

voidloop()                     // run over and overagain

{

  digitalWrite(ledPin, HIGH);   // sets the LED on

  delay(500);                  // waits for a second

  digitalWrite(ledPin, LOW);    // sets the LED off

  delay(500);                  // waits for a second

}

If you try to save thesketch, you’ll get the warning that it’s read-only.

 Not a big deal, you can save it under a new name, such as MyBlink

Once the Arduino hasbeen updated with the new sketch you should see a faster-blinking light thanbefore

If the LED is notblinking faster, check:

·                 Did you make the changesto the delay procedure call to make it 500?

·                 Did the compile/verifycomplete successfully? (should look like the screenshot above)

·                 Did the upload completesuccessfully? (should look like the screenshot above)