Last Updated: 20/07/2021

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Functions Lesson 1 - digitalWrite()

Functions >> Functions Lesson 1 - digitalWrite()

Lesson Contents

Using a Digital Pin
What pins are digital and which ones to use
Using the function digitalWrite();
Understanding HIGH and LOW
Using the function pinMode()
Understanding OUTPUT and INPUT
Defining a constant integer (const int)
Using the built in LED.
Problems with LED_BUILTIN
Writing a better "blink" sketch

Example 1: blinkv2.ino

Click to Download code:blinkv2.ino

Using the function digitalWrite();
Understanding HIGH and LOW
Using the function pinMode()
Understanding OUTPUT and INPUT
Defining a constant integer (const int)
Using the built in LED.
Problems with LED_BUILTIN

 
/* An improved version of the blink sketch.
 * blinkv2
 * 
 * Removing the use of LED_BUILTIN
 * Defining our pin
 * Understanding pinMode()
 * Understanding digitalWrite()
 * Understanding HIGH and LOW and it's alternatives
 * 
 * pin 13 ...LED
 */
 // This line is OK, but using const int is much better and safer
 //int ledPin = 13;//pin 13 has a built in LED
 
 //const int is an int that cannot have it's value changed
 const int ledPin = 13;//pin 13 has a built in LED

// the setup function runs once when you press reset or power the board
void setup() {
   // Serial.begin(9600) starts serial communication. 9600bps bits per second = 1200 characters per second
  Serial.begin(9600);
  //Send script name
  Serial.println("blinkv2...");
  //this will print a blank line
  Serial.println(" ");
  
  //The original LED_BUILTIN in has been removed as it can lead to bad habits in not defining a variable
  //Also it will not work on other makes of board.
  //pinMode(LED_BUILTIN, OUTPUT);

  //A digital pin can be an INPUT or an OUTPUT. Input is used to read incoming data, OUTPUT makes the pin
  //into a digital switch to send outgoing data.
  pinMode(ledPin, OUTPUT);
  
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(ledPin, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(ledPin, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}

Example 2: blinkv3.ino

Click to Download code:blinkv3.ino

Alternatives to using HIGH and LOW
using a Constant Integer (const int) instead of HIGH and LOW

 
/* An improved version of the blink sketch.
 * blinkv3
 * 
 * Removing the use of LED_BUILTIN
 * Defining our pin
 * Understanding pinMode()
 * Understanding digitalWrite()
 * Understanding HIGH and LOW and it's alternatives
 * 
 * pin 13 ...LED
 */

 
 //const int is an int that cannot have it's value changed
 const int ledPin = 13;//pin 13 has a built in LED
 const int turnOnLED = 1;
 const int turnOffLED = 0;

// the setup function runs once when you press reset or power the board
void setup() {
   // Serial.begin(9600) starts serial communication. 9600bps bits per second = 1200 characters per second
  Serial.begin(9600);
  //Send script name
  Serial.println("blinkv3...");
  //this will print a blank line
  Serial.println(" ");
  
  //The original LED_BUILTIN in has been removed as it can lead to bad habits in not defining a variable
  //Also it will not work on other makes of board.
  //pinMode(LED_BUILTIN, OUTPUT);
  pinMode(ledPin, OUTPUT);//A pin can be an INPUT or an OUTPUT
  
}

// the loop function runs over and over again forever
void loop() {
  //this is good
  digitalWrite(ledPin, HIGH);   // turn the LED on (HIGH is 5 volts)
  delay(1000);                       // wait for a second
  digitalWrite(ledPin, LOW);    // turn the LED off by making the voltage LOW 0 volts
  delay(1000); // wait for a second
  
  //This code is good as it is clear what is happening
  //Turn the ledPin (pin 13) on (HIGH) with a variable turnOnLED that has a value of 1 (not equal to Zero) so could be -2, -200, +35, 64
  digitalWrite(ledPin,turnOnLED);
  //wait half a second
  delay(500);
  //Turn the ledPin (pin 13) off (LOW) with a variable turnOffLED that has a value of 0
  digitalWrite(ledPin,turnOffLED);
  delay(500);
  
  
  //Below is NOT a good way to write code, although the code works it would quickly become very confusing.
  
  //by calling pin 13 directly we no longer know what pin 13 does, this causes confusion in larger sketches
  digitalWrite(13, 1);//Although the value 1 makes the pin HIGH, it would be better with a variable name
  delay(500);
  digitalWrite(13, 0);//LOW equals 0 but again would be better with a variable name
  delay(500);
  
}

Additional Resource Links

Don't forget to use the Reference in you Arduino IDE for more help on this lesson.

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