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# Arduino: Lesson 9 - LED Sequencing using Array Data Structure

## Welcome to Lesson 9 - Basic Arduino Course

In today's lesson, we will learn how to use 5 LEDs connected to 5 Arduino ports, which will light up in sequence and right after the cycle ends, will go out in sequence. With that, we will learn a new instruction, the Array data structure.

## What is Array?

An array is a collection of variables that are accessed with an index number. However, the "array" data structure is not exactly an existing data type

There are arrays of variables like "char", "int", "boolean", "float" and so on. This means that an array can be variables of any type mentioned above.

An array, or vector, for example, is a collection of variables of a specific type, which may even use the same nomenclature, but which will be distinguished by an indexed number.

For example: We can use a variable type "float" with a single name indexed by number, instead of different variables (VarFloat_1, VarFloat_2, VarFloat_3...) we can use a single grouped array with the same nomenclature that will allow each variable be manipulated separately by a numerical index, (VarFloat , VarFloat , VarFloat  ...).

## Hardware Required

• Arduino Board
• 5 - LEDs
• 5 - 200 ohms resistor - (brown, green, brown, gold)
• Jumper Wires
• Protoboard (optional)

## The Circuit Connections

The circuit is a bit simple, we connect the longer "Anode" legs of the 5 LEDs to the positive 5V of the Arduino, and the other shorter leg "Cathode", we connect to the 150 ohm resistor and in series with GND, negative of the Arduino, as shown in Figure 2 below. Fig. 2 -  LED Sequencing using Array Data Structure - tinkercad.com

We use a protoboard to facilitate the connections, but you can also connect the wires directly to the Arduino.

## The Code

The code can be implemented in the normal way in programming, as shown in the code below. But the code is quite large, we use 42 lines of code to create this kind of sequential LED circuit. To write less lines of code, an "optimizer" is required.

 123456789101112131415161718192021222324252627282930313233343536373839404142 // Arduino: Lesson 9 - LED Sequencing using Array Data Structureconst int Led1 =  2;        // Select the output LED1 PINconst int Led2 =  3;        // Select the output LED2 PINconst int Led3 =  4;        // Select the output LED3 PINconst int Led4 =  5;        // Select the output LED4 PINconst int Led5 =  6;        // Select the output LED5 PINvoid setup() {                // This function is called once when the program starts   pinMode(Led1, OUTPUT);    // Initialize digital pin LED1 as an output. pinMode(Led2, OUTPUT);    // Initialize digital pin LED2 as an output. pinMode(Led3, OUTPUT);    // Initialize digital pin LED3 as an output. pinMode(Led4, OUTPUT);    // Initialize digital pin LED4 as an output. pinMode(Led5, OUTPUT);    // Initialize digital pin LED5 as an output.}void loop() { // The loop function runs over and over again as long as the Arduino has power.// Turn ON each  LED sequence in order  digitalWrite(Led1, HIGH);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led2, HIGH);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led3, HIGH);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led4, HIGH);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led5, HIGH);  delay(150);                             // Wait for 150 millisecond(s)// Turn OFF each  LED sequence in order  digitalWrite(Led1, LOW);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led2, LOW);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led3, LOW);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led4, LOW);  delay(150);                             // Wait for 150 millisecond(s)  digitalWrite(Led5, LOW);  delay(150);                             // Wait for 150 millisecond(s)}//------------------------------------- www.elcircuits.com --------------------------------------------

This is where the Array data structure comes into play, we can use it to drastically reduce the number of lines of code, as shown in the code example below.

 123456789101112131415161718192021 // Arduino: Lesson 9 - LED Sequencing using Array Data Structureconst int Leds =  5;                                      //Number of LEDs in the circuitconst int PinLeds[Leds] = {2, 3, 4, 5, 6};   //LEDs connected to pins 2 to 6void setup() {                 // This function is called once when the program starts  for (int i = 0; i < Leds; i++) {            // Go through each of the elements in our array    pinMode(PinLeds[i], OUTPUT);    // And set them as OUTPUT  }}void loop() { // The loop function runs over and over again as long as the Arduino has power.  for (int i = 0; i < Leds; i++) {            // Go through each of the Leds elements in our array    digitalWrite(PinLeds[i], HIGH);     // And set each of the PinLeds in HIGH level    delay(150);                                      // Wait 150 millis seconds, and back to structure For     }  for (int i = 0; i < Leds; i++) {            // Go through each of the Leds elements in our array    digitalWrite(PinLeds[i], LOW);      // And set each of the PinLeds in LOW level    delay(150);                                      // Wait 150 millis seconds, and back to structure For   }}//------------------------------------- www.elcircuits.com --------------------------------------------

Using the Array Data Structure technique, we could practically save half a line of the previous code, that's really cool, right?

After building the circuit, connect your Arduino board to your computer, run the Arduino software (IDE), copy the code below and paste it into your Arduino IDE. But first let us understand the code line by line.
• In Line 3, we declared  the number of LEDs in the circuit.

• In Line 4, We are using an Array to index each pin of the LEDs in the corresponding Arduino Ports.
 12345... // Arduino: Lesson 9 - LED Sequencing using Array Data Structureconst int Leds =  5;                                      //Number of LEDs in the circuitconst int PinLeds[Leds] = {2, 3, 4, 5, 6};   //LEDs connected to pins 2 to 6//------------------------------------- www.elcircuits.com --------------------------------------------
• In Line 6we enter the void setup() function. This function is read only once when the Arduino is started.

• In Line 7, we enter in the FOR structure control, to access each Leds element.

• in Line 8, we set each PinLeds as OUTPUT, through each elements in ou array.
 1...678910... // Arduino: Lesson 9 - LED Sequencing using Array Data Structurevoid setup() {                 // This function is called once when the program starts  for (int i = 0; i < Leds; i++) {            // Go through each of the elements in our array    pinMode(PinLeds[i], OUTPUT);    // And set them as OUTPUT  }}//------------------------------------- www.elcircuits.com --------------------------------------------
• Line 11, we enter in the loop() function does precisely what its name suggests, and loops consecutively.

• In Line 12, we enter in the For structure control, to go through each of the Leds elements in our array.

• In Line 13, we continue in the For structure control, and set each of the PinLeds in HIGH level, turn on Led by Led.

• In Line 14, we enter in the delay function, to wait 150 millis seconds, and back to structure For while it is true.

• In Line 16, we enter in the For structure control, to go through each of the Leds elements in our array.

• In Line 17, we continue in the For structure control, and set each of the PinLeds in LOW level, turn off Led by Led.

• In Line 18, we enter in the delay function, to wait 150 millis seconds, and back to structure For while it is true.
 1...1112131415161718192021 // Arduino: Lesson 9 - LED Sequencing using Array Data Structurevoid loop() { // The loop function runs over and over again as long as the Arduino has power.  for (int i = 0; i < Leds; i++) {            // Go through each of the Leds elements in our array    digitalWrite(PinLeds[i], HIGH);     // And set each of the PinLeds in HIGH level    delay(150);                                      // Wait 150 millis seconds, and back to structure For     }  for (int i = 0; i < Leds; i++) {            // Go through each of the Leds elements in our array    digitalWrite(PinLeds[i], LOW);      // And set each of the PinLeds in LOW level    delay(150);                                      // Wait 150 millis seconds, and back to structure For   }}//------------------------------------- www.elcircuits.com --------------------------------------------
All ready! After you have assembled the entire circuit, and uploaded this code, what you should see is the sequence of LEDs turning on and off, giving the impression that the LEDs are moving forward.