LESSON 11 – VOID FUNCTIONS

FUNCTIONS

A function is simply a section of code that is organized together to perform a task. We can execute the code inside the function by calling the function with its name.

TWO KEY FUNCTIONS

Arduino programs require that you have a setup() function and a loop() function. These two functions are special because they are autimatically called by the Arduino.

However, we can create other functions that we can call on our own.

MODULARITY

Functions allow us to organize code and give it a name. By doing so, we are able to think on a higher level about the task at hand because the problem is broken down in many parts.

VOID

Some functions are used to calculate something and then return the calculated value to where they were called. Other functions do not return anything and are used to make something happen (such as output something to screen or turn on LEDs). Such functions are void functions.

EXAMPLE 1

The following program/circuit will create a void function called blinkLED(). This function will take care of turning an LED on for 1 second and then turning it off.

We then call this function from inside the loop() function. To provide some variation, inside the loop() function, we have a delay that ranges from 0 to 5 seconds.

CIRCUIT

Connect pin 2 to an LED, then to resistor, then to ground.

CODE

int ledPin;

void setup()

{

ledPin = 2;

pinMode(ledPin, OUTPUT);

}

void loop()

{

blinkLED();

delay(random(5000));

}

void blinkLED()

{

digitalWrite(ledPin, HIGH);

delay(1000);

digitalWrite(ledPin,LOW);

}

PARAMETERS

It is sometimes important to provide information to a function. For example, in the program above, perhaps we want to state how long the blinkLED() function should light up the LED. We can do this using parameters (or arguments).

EXAMPLE 2

The following example is the same as the previous one except the blinkLED() function now has a parameter that states how long the LED should light up. Notice that the call to that function provides the matching information.

CIRCUIT

Connect pin 2 to an LED, then to resistor, then to ground.

CODE

int ledPin;

void setup()

{

ledPin = 2;

pinMode(ledPin, OUTPUT);

}

void loop()

{

blinkLED(2000);

delay(random(5000));

blinkLED(500);

delay(random(5000);

}

void blinkLED(int duration)

{

digitalWrite(ledPin, HIGH);

delay(duration);

digitalWrite(ledPin,LOW);

}

The parameter called duration is an integer. It is just like any other variable except it gets its value from the function call. So above, duration gets the value 2000 for the first call and the value 500 for the next one.

TRY THIS…

PRACTICE 11-1

RESEARCH

Before starting, go research a little bit about Morse code. You should understand what a dot and a dash are.

CIRCUIT

Series circuit: From pin #2, go to an LED. From the LED go to a resistor. From the resistor, go to ground.

CODE

You will write a program that will display SOS in morse code using the LED in your circuit.

STEP 1 – GLOBAL VARIABLES

First, you need a global variable that will hold your base period of time. I’d set it to 1000 to start. This will be slow enough for Morse code newbies like us to read the message.

You also need a variable called ledPin that will hold the number of the pin connected to the LED.

STEP 2 – SETUP

Inside setup, give values to your two global variables from above. Also set the pinMode for the ledPin to OUTPUT.

STEP 3 – VOID FUNCTIONS

You need to create all of these void functions:

dot() – Puts LED on for one period of time

dash() – Puts LED on for three periods of time

gap() – Puts LED off for one period of time

gapLetter() – Puts LED off for three periods of time

gapWord() – Puts LED off for seven periods of time

STEP 4 – LOOP

Inside loop, put the functions calls needed to display S, then O and then S. For example, for S, we need:

dot();

gap();

dot();

gap();

dot();

gapLetter();

That’s it!