LED Sign Example. Photo Credit: animationlibrary.com

Welcome back for another round of learning Arduino! I just want to take a moment to thank those who are continuing this journey with me.  For those just joining us, please take a look at Part 1, Part 2, and Part 3 to clear up any questions!  I personally have come a long way since my start in Summer and have worked on some really awesome projects this past quarter.  Through the use of my personal Arduino starter kit, I have been able to build an obstacle avoiding car, a temperature controlling HVAC system, and a self-stabilizing wing.  These projects were completed for a Control of Mechanical Systems class I took this past quarter and I can’t wait to share them all with you.

In Part 3, we were able to build a simple circuit and breakdown the code to control the circuit.  It was a nice intro project that showed how to setup an Arduino code and upload it to the board.  This time around the task will be slightly more involved but will show you important coding practices to make future projects more manageable.  We will be controlling multiple LED’s and manipulating their states at any given time.  Let’s get to it!

What you need:

• 8 x LED’s (any color)
• 8 x 330Ohm Resistors (if you don’t know what you have, the color code is orange-orange-brown)
• Arduino board
• Breadboard
• Assorted Jumpers

Friendly Note: We are not responsible for any misuse or risky behavior!

Photo Credit: Vilros Starter Kit Guide by Sparkfun

Place the LED’s anywhere on the breadboard, without plugging any two legs into the same rows.  This can cause a short and you will experience unwanted circuit behavior.  Also, take care in knowing which leg is the longer length (positive) and the shorter length (negative).  You may want to place the LED’s in an organized fashion so that the light sequencing looks nice.  Remember, we want to place a resistor in series with the LED’s to protect them from excess current.  Next, place jumpers from the positive LED legs to the Arduino inputs such as digital inputs 2 -9.  Finally, apply a 5V potential to the positive(+) column on the breadboard and a ground jumper to the negative (-) column.  Take a look above for a better view of the circuit layout!

Code

The code below is VERY good at teaching what each part does.  Instead of re-analyzing each part again, I will add to it in hopes of clarifying any questions.  Simply copy and paste it into your IDE and upload it to your Arduino board.  I have included a video demonstration below the code to give you a better visual of what to expect once you run it.

/*

This sketch was written by SparkFun Electronics,

with lots of help from the Arduino community.

This code is completely free for any use.

Visit http://www.arduino.cc to learn about the Arduino.

Version 2.0 6/2012 MDG

*/

// To keep track of all the LED pins, we’ll use an “array”.

// An array lets you store a group of variables, and refer to them

// by their position, or “index”. Think of it as empty boxes that you

//are assigning a value to and that you can address at any time!

//Here we’re creating an array of

// eight integers, and initializing them to a set of values:

int ledPins[] = {2,3,4,5,6,7,8,9};

// The first element of an array is index 0.

// We’ve put the value “2” in index 0, “3” in index 1, etc.

// The final index in the above array is 7, which contains

// the value “9”.

// We’re using the values in this array to specify the pin numbers

// that the eight LEDs are connected to. LED 0 is connected to

// pin 2, LED 1 is connected to pin 3, etc.

void setup()

{

int index;

// In this sketch, we’ll use “for() loops” to step variables from

// one value to another, and perform a set of instructions for

// each step. For() loops are a very handy way to get numbers to

// count up or down.

// Every for() loop has three statements separated by

// semicolons (;):

//   1. Something to do before starting

//   2. A test to perform; as long as it’s true, keep looping

//   3. Something to do after each loop (increase a variable)

// For the for() loop below, these are the three statements:

//   1. index = 0;    Before starting, make index = 0.

//   2. index <= 7;   If index is less or equal to 7,

//                    run the following code.

//                                          (When index = 8, continue with the sketch.)

//   3. index++  Putting “++” after a variable means

//                    “add one to it”.

//                                          (You can also use “index = index + 1”.)

// Every time you go through the loop, the statements following

// the for() (within the brackets) will run.

// When the test in statement 2 is finally false, the sketch

// will continue.

// Here we’ll use a for() loop to initialize all the LED pins

// to outputs. This is much easier than writing eight separate

// statements to do the same thing.

// This for() loop will make index = 0, then run the pinMode()

// statement within the brackets. It will then do the same thing

// for index = 2, index = 3, etc. all the way to index = 7.

for(index = 0; index <= 7; index++)

{

pinMode(ledPins[index],OUTPUT);

// ledPins[index] is replaced by the value in the array.

// For example, ledPins[0] is 2

}

}

void loop()

{

// This loop() calls functions that we’ve written further below.

// We’ve disabled some of these by commenting them out (putting

// “//” in front of them). To try different LED displays, remove

// the “//” in front of the ones you’d like to run, and add “//”

// in front of those you don’t to comment out (and disable) those

// lines.

oneAfterAnotherNoLoop();  // Light up all the LEDs in turn

//oneAfterAnotherLoop();  // Same as oneAfterAnotherNoLoop,

// but with much less typing

//oneOnAtATime();         // Turn on one LED at a time,

// scrolling down the line

//pingPong();             // Light the LEDs middle to the edges

//marquee();              // Chase lights like you see on signs

//randomLED();            // Blink LEDs randomly

}

/*

oneAfterAnotherNoLoop()

This function will light one LED, delay for delayTime, then light

the next LED, and repeat until all the LEDs are on. It will then

turn them off in the reverse order.

This function does NOT use a for() loop. We’ve done it the hard way

to show you how much easier life can be when you use for() loops.

Take a look at oneAfterAnotherLoop() further down, which does

exactly the same thing with much less typing.

*/

void oneAfterAnotherNoLoop()

{

int delayTime = 100; // time (milliseconds) to pause between LEDs

// make this smaller for faster switching

// turn all the LEDs on:

digitalWrite(ledPins[0], HIGH);  //Turns on LED #0 (pin 2)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[1], HIGH);  //Turns on LED #1 (pin 3)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[2], HIGH);  //Turns on LED #2 (pin 4)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[3], HIGH);  //Turns on LED #3 (pin 5)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[4], HIGH);  //Turns on LED #4 (pin 6)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[5], HIGH);  //Turns on LED #5 (pin 7)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[6], HIGH);  //Turns on LED #6 (pin 8)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[7], HIGH);  //Turns on LED #7 (pin 9)

delay(delayTime);                //wait delayTime milliseconds

// turn all the LEDs off:

digitalWrite(ledPins[7], LOW);   //Turn off LED #7 (pin 9)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[6], LOW);   //Turn off LED #6 (pin 8)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[5], LOW);   //Turn off LED #5 (pin 7)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[4], LOW);   //Turn off LED #4 (pin 6)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[3], LOW);   //Turn off LED #3 (pin 5)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[2], LOW);   //Turn off LED #2 (pin 4)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[1], LOW);   //Turn off LED #1 (pin 3)

delay(delayTime);                //wait delayTime milliseconds

digitalWrite(ledPins[0], LOW);   //Turn off LED #0 (pin 2)

delay(delayTime);                //wait delayTime milliseconds

}

/*

oneAfterAnotherLoop()

This function does exactly the same thing as oneAfterAnotherNoLoop(),

but it takes advantage of for() loops and the array to do it with

much less typing.

*/

void oneAfterAnotherLoop()

{

int index;

int delayTime = 100; // milliseconds to pause between LEDs

// make this smaller for faster switching

// Turn all the LEDs on:

// This for() loop will step index from 0 to 7

// (putting “++” after a variable means add one to it)

// and will then use digitalWrite() to turn that LED on.

for(index = 0; index <= 7; index++)

{

digitalWrite(ledPins[index], HIGH);

delay(delayTime);

}

// Turn all the LEDs off:

// This for() loop will step index from 7 to 0

// (putting “–” after a variable means subtract one from it)

// and will then use digitalWrite() to turn that LED off.

for(index = 7; index >= 0; index–)

{

digitalWrite(ledPins[index], LOW);

delay(delayTime);

}

}

/*

oneOnAtATime()

This function will step through the LEDs,

lighting only one at at time.

*/

void oneOnAtATime()

{

int index;

int delayTime = 100; // milliseconds to pause between LEDs

// make this smaller for faster switching

// step through the LEDs, from 0 to 7

for(index = 0; index <= 7; index++)

{

digitalWrite(ledPins[index], HIGH);  // turn LED on

delay(delayTime);                    // pause to slow down

digitalWrite(ledPins[index], LOW);   // turn LED off

}

}

/*

pingPong()

This function will step through the LEDs,

lighting one at at time in both directions.

*/

void pingPong()

{

int index;

int delayTime = 100; // milliseconds to pause between LEDs

// make this smaller for faster switching

// step through the LEDs, from 0 to 7

for(index = 0; index <= 7; index++)

{

digitalWrite(ledPins[index], HIGH);  // turn LED on

delay(delayTime);                    // pause to slow down

digitalWrite(ledPins[index], LOW);   // turn LED off

}

// step through the LEDs, from 7 to 0

for(index = 7; index >= 0; index–)

{

digitalWrite(ledPins[index], HIGH);  // turn LED on

delay(delayTime);                    // pause to slow down

digitalWrite(ledPins[index], LOW);   // turn LED off

}

}

/*

marquee()

This function will mimic “chase lights” like those around signs.

*/

void marquee()

{

int index;

int delayTime = 200; // milliseconds to pause between LEDs

// Make this smaller for faster switching

// Step through the first four LEDs

// (We’ll light up one in the lower 4 and one in the upper 4)

for(index = 0; index <= 3; index++) // Step from 0 to 3

{

digitalWrite(ledPins[index], HIGH);    // Turn a LED on

digitalWrite(ledPins[index+4], HIGH);  // Skip four, and turn that LED on

delay(delayTime);                      // Pause to slow down the sequence

digitalWrite(ledPins[index], LOW);     // Turn the LED off

digitalWrite(ledPins[index+4], LOW);   // Skip four, and turn that LED off

}

}

/*

randomLED()

This function will turn on random LEDs. Can you modify it so it

also lights them for random times?

*/

void randomLED()

{

int index;

int delayTime;

// The random() function will return a semi-random number each

// time it is called. See http://arduino.cc/en/Reference/Random

// for tips on how to make random() even more random.

index = random(8);       // pick a random number between 0 and 7

delayTime = 100;

digitalWrite(ledPins[index], HIGH);  // turn LED on

delay(delayTime);                    // pause to slow down

digitalWrite(ledPins[index], LOW);   // turn LED off

}

Video Demonstration:

Here’s what you should expect to see in your circuit!  Enjoy!

In future projects you will most likely need to use For Loops and Arrays to complete tasks efficiently and to consolidate writing space.  These components of code show up in all different forms of script such as VBA and Matlab so learning it now will make you better prepared.  Have some fun with the code above by playing with the timing of delays and with the mixing of functions.  If you’re wondering what multiple LED’s are even used for just imagine a marquee display.  They are made up of a bunch of LED’s that turn on and off independently to form a desired letter, symbol, or shape.

Thanks for reading Part 4 of my Learning Arduino series and don’t forget to visit our GoFundMe site to help us reach our fundraising goal!

Until next time!