Let’s see some basic functions related to Startup and GPIO that are frequently used in Arduino IDE.

Arduino Functions at startup

a)  setup()

• This function is called at the beginning of the sketch.
• It is used for initializing variables, pin modes etc.
• It runs only once after each power up, or when the Arduino board resets.

b)  loop()

• Once the setup function is completed, the loop function is executed over and over continuously. 

Arduino Functions for GPIO

a)  pinMode(pin,mode)

• pin : The pin for which a specific mode is selected.
• mode : The mode for the pin specified in the function. It can be INPUT, INPUT PULLUP or OUTPUT.
• This function is used to configure the pin specified to behave as Input (INPUT), Input with pull up resistor (INPUT_PULLUP), or Output (OUTPUT).

e.g.

pinMode(3,INPUT) //configures digital pin 3 as an input pin.

b)  digitalRead(digital_pin)

• digital_pin : The digital pin which is to be read.
• This function is used to read the digital signal from the specified digital pin (digital_pin).
• Arduino UNO board has 14 digital pins 0 to 13.
• The function returns either HIGH or LOW.

e.g.

digitalRead(5) //reads value on pin 5.

c)  digitalWrite(pin,value)

• pin : The digital pin to which value is to be written.
• value : Can be HIGH or LOW.
• This function is used to write a HIGH or a LOW value to a digital pin.

e.g.

digitalWrite(4, HIGH) //makes the pin 4 HIGH.

On board LED blinking code for Arduino UNO

/* Blinking on-board LED connected to pin 13 of Arduino UNO */


/* Setup is run once at the start (Power-On or Reset) of sketch */
void setup()
{
    pinMode(13, OUTPUT); 		/* Pin 13 is defined as Output */
}

/* Loop runs over and over after the startup function */
void loop()
{
    digitalWrite(13, HIGH); 	/* Make pin 13 High, LED ON */
    delay(1000); 				/* Wait for 1 second */
    digitalWrite(13, LOW); 		/* Make pin 13 Low, LED OFF*/
    delay(1000); 				/* Wait for 1 second */
}

Arduino Function for Analog Read

d)  analogRead(analog_pin)

• analog_pin : The analog pin whose value is to be read.
• This function is used to read the analog signal from the specified analog pin (analog_pin).
• UNO board has 6 ADC channels A0 to A5.
• The function returns an integer value in the range of 0 to 1023.

e.g.

analogRead(A3) //reads the value on analog pin A3.

Arduino analogRead Code

Reading analog value from an analog sensor connected to pin A1 of Arduino and displaying the ADC value on serial monitor of Arduino

/* Read analog value on analog pin A1 of Arduino UNO and print the ADC value on Serial Monitor*/


/* Setup is run once at the start (Power-On or Reset) of sketch */
void setup()
{
    Serial.begin(9600); /* opens serial port, sets data rate to 9600 bps */
}

/* Loop runs over and over after the startup function */
void loop()
{
    int adc_val;
    adc_val = analogRead(A1); /* Read analog signal present on pin A1 */
    Serial.print("ADC value is : "); /* Print */
    Serial.println(adc_val); /* Print with \r\n */
    delay(5000); /* Wait for 5 seconds */
}

Arduino Function for Analog Write

e)  analogWrite(pin,value)

• pin : The analog pin to which value is to be written.
• value : Can be any number between 0 to 255. 0 being 0% duty cycle and 255 being 100% duty cycle.
• This function is used for generating PWM on PWM digital pins(pins 3,5,6,9,10,11 for Arduino UNO.
• value can be any number between 0 to 255. 0 being 0% duty cycle and 255 being 100% duty cycle.

e.g.

analogWrite(3, 128) //generates a PWM wave of 50% duty cycle on pin 3.

Arduino analogWrite Code

Vary intensity of LED connected to pin 5 of Arduino by generating PWM wave of varying duty cycle

/* Vary intensity of external LED connected to pin 5 of Arduino UNO  */


/* Setup is run once at the start (Power-On or Reset) of sketch */
void setup()
{
    pinMode(5, OUTPUT);  /* Pin 5 is defined as Output */
}

/* Loop runs over and over after the startup function */
void loop()
{
    for(int i =0; i<256; i++)
     {
        analogWrite(5, i); /* Vary intensity of LED connected externally to pin 5 of Arduino */
        /* Vary the intensity by applying PWM of duty cycle varying from 0 to 100% (writing value 0 to 255) */
        delay(300); /* Wait for 300 milliseconds */
     }
}