Arduino 101
Basic Programming Concepts

Nick Borko

September 28, 2013

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Except where otherwise noted, this work is licensed under
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Agenda

Introduction
Arduino Programming Basics
- Minimum Program Structure
- Input, Output and Delays
C++ Programming Concepts
- Types and Variables
- Conditionals, Loops and Functions
Conclusion

Arduino Programming Basics

Arduino programs are written in C++
Arduino programs are built on the Arduino Core
- Handles boilerplate initialization code
- Provides high-level interfaces to control AVR functions
- Automatically linked to the Arduino program
Compiling, linking and uploading is handled by the IDE

Arduino Programming Basics:

Arduino Program Structure

The minimum Arduino program defines 2 functions:
- setup() is called when the program starts and runs once, normally used for pin and variable initialization
- loop() is called continuously after setup() finishes executing (i.e., as an endless loop)
Every Arduino program must define both setup() and loop(), although either (or both!) may be empty

Arduino Programming Basics:

Arduino Program Structure

The minimum Arduino program defines 2 functions:

// A minimal Arduino program
// NOTE: Comments start with //
void setup () {
  // do nothing one time!
}

void loop() {
  // do nothing over and over!
}

This program is remarkably uninteresting

Arduino Programming Basics:

Input and Output

The Arduino can also run more interesting programs by reading input and sending output (the whole point to programming!)
Input is read from and output is sent to pins on the AVR microprocessor
The Arduino board breaks out these pins to headers, which can be used to read and write digital and analog signals

Arduino Programming Basics:

Input and Output

Arduino digital input/output pins are numbered 0-13 (for a total of 14 pins)
- Pins 0 and 1 are reserved for serial communication (don't use these!)
- Pins 2 and 3 can be configured for external interrupts
- Pins 3, 5, 6, 9, 10 and 11 are capable of Pulse Width Modulation (PWM) analog output
- Pins 10-13 can be used for SPI (serial) communication

Arduino Programming Basics:

Input and Output

Arduino analog input pins are numbered A0-A5 (for a total of 6 pins)
- Can read an analog values between 0 and 1023 based on a reference voltage (labeled AREF on the Arduino)
- Can also be used as additional digital input/output pins, numbered 14-19
- Pins A4 and A5 can be used for TWI ("2-wire" interface), compatible with I²C (Inter-Integrated Circuit)

Arduino Programming Basics:

Input and Output

Pins must be set up for input or output before they can be used:
pinMode(PIN, MODE);
- PIN is a pin number 0-19 or A0-A5
- MODE is either INPUT or OUTPUT
Usually called in the setup() function
You don't need to set the pin mode for a pin you're not using (i.e. not connected)

Arduino Programming Basics:

Input and Output

Example from the Blink sketch

void setup() {
  // initialize the digital pin as an output.
  // Pin 13 has an LED connected on most Arduino boards:
  pinMode(13, OUTPUT);
}

Arduino Programming Basics:

Input and Output

Digital input is read from a selected pin:
value = digitalRead(PIN);
- PIN is a pin number 0-13
- value is returned as either LOW or HIGH
Digital output is written to a selected pin:
digitalWrite(PIN, VALUE);
- PIN is a pin number 0-19
- VALUE is either LOW or HIGH

Arduino Programming Basics:

Input and Output

Example from the Blink sketch

void loop() {
  digitalWrite(13, HIGH); // set the LED on
  delay(1000);            // wait for a second
  digitalWrite(13, LOW);  // set the LED off
  delay(1000);            // wait for a second
}

Arduino Programming Basics:

Input and Output

Analog input is read from an analog pin:
value = analogRead(PIN);
- PIN is a pin number A0-A5 (or 14-19)
- value is returned as a number 0-1023
Analog output is written to a PWM pin:
analogWrite(PIN, VALUE);
- PIN is a pin number 3, 5, 6, 9, 10 or 11
- VALUE is a number from 0 to 255

Arduino Programming Basics:

Input and Output

There are other ways to do input and output:
- tone()
- shiftIn()
- shiftOut()
- pulseIn()
- SPI, SoftwareSerial and Wire libraries
Except for tone(), we won't be covering these in this workshop

Arduino Programming Basics:

Killing Time

Simple sketches can use the delay() and delayMicroseconds() functions
- delay() takes a numerical argument for the number of milliseconds (0.001 seconds) to delay execution
- delayMicroseconds() takes a numerical argument for the number of microseconds (0.000001 seconds), up to 16k microseconds
Program execution "halts" during a delay, so use with care

Arduino Programming Basics:

Killing Time

Example from the Blink sketch

void loop() {
  digitalWrite(13, HIGH); // set the LED on
  delay(1000);            // wait for a second
  digitalWrite(13, LOW);  // set the LED off
  delay(1000);            // wait for a second
}

C++ Programming Concepts

Although the programming environment is based on Processing, the programming language for Arduino is C++
- Variables are typed (strongly) and must be declared before use
- Statements end with a semicolon ;
- Curly braces {} are used to mark program blocks
- Single line comments begin with //, multiline comments are marked with /* ... */

C++ Programming Concepts

Types and Variables

All variables and data have a type
- C++ types: int, float, char, bool, void, et. al.
- Arduino types: boolean, byte, string, array
All variables must be declared before use
- Variable declarations can appear anywhere, as long as it's before a reference
- Variables can be initialized in the declaration
- Variables are scoped by execution block
Variable names start with a letter or _

C++ Programming Concepts:

Types and Variables

Variables can be assigned values and used in expressions

int a = 2;
int b = 3;
int c;
c = a + b;     // c now has a value of 5
c = b * 4;     // c now has a value of 12
a = a + 1;     // a now has a value of 3
c = a * b – c; // c now has a value of -3

If you haven't programmed before, don't worry about it; you won't be writing code

C++ Programming Concepts:

Types and Variables

Example from the Fade sketch

int brightness = 0; // how bright the LED is
int fadeAmount = 5; // how many points to fade the LED by

void setup() {
  // declare pin 9 to be an output:
  pinMode(9, OUTPUT);
}

void loop() {
  // set the brightness of pin 9:
  analogWrite(9, brightness);
  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;
  // reverse the direction of the fading at the ends of the fade:
  if (brightness == 0 || brightness == 255) {
    fadeAmount = -fadeAmount ;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}

C++ Programming Concepts

Conditionals

C++ has if/else and switch/case control structures, but we will only cover if/else
The if/else statements allow conditional execution of code
- If an expression evaluates to "true," then the code block following an if statement is executed
- If the expression evaluates to "false," then the code block follow the adjoining else statement is executed

C++ Programming Concepts

Conditionals

All expressions evaluate to "true" or "false," where "false" is defined as "0" (zero), and "true" is anything else
Boolean expressions evaluate to true or false
- Equality (==) and inequality (!=)
- Numerical comparisons (<, >, <=, >=)
- Boolean operators not (!), and (&&), or (||)
- Note that string comparisons use functions

C++ Programming Concepts:

Conditionals

Example from the Fade sketch

int brightness = 0; // how bright the LED is
int fadeAmount = 5; // how many points to fade the LED by

void setup() {
  // declare pin 9 to be an output:
  pinMode(9, OUTPUT);
}

void loop() {
  // set the brightness of pin 9:
  analogWrite(9, brightness);
  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;
  // reverse the direction of the fading at the ends of the fade:
  if (brightness == 0 || brightness == 255) {
    fadeAmount = -fadeAmount ;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}

C++ Programming Concepts

Loops

Loops allow a block of code to be executed more than once without duplicating code
C++ supports for and while loops
You won't be writing any code for this workshop, but you do need to recognize loops in code

C++ Programming Concepts

Loops

The while loop executes a code block as long as the condition is true
```
while(condition) {
  // code block
}
```

A do...while construct is also available

do {
  // code block
} while(condition);

C++ Programming Concepts

Loops

The for loop is just a modified while loop
```
for(init; condition; loop statement) {
  // code block
}
```
- init is a statement that is executed once before the loop begins
- The code block is executed as long as the condition is true (as in a while loop)
- The loop statement is executed at the end of each iteration of the code block

C++ Programming Concepts

Loops

The for loop is just a modified while loop

for(init; condition; loop statement) {
  // code block
}

This is exactly equivalent to:

init;
while(condition) {
  // code block
  loop statement;
}

C++ Programming Concepts

Functions

A function is a group of statements that is executed when it is called from some point of the program
Functions allow you to execute the same code block at different places in your program
You are already writing functions, setup() and loop()

C++ Programming Concepts

Functions

Functions can take parameters and return values

Function examples:

void blinkLed(int pin, int milliseconds) {
  digitalWrite(pin, HIGH);
  delay(milliseconds);
  digitalWrite(pin, LOW);
}

int celsuisToFahrenheit(int degrees) {
  return degrees * 1.8 + 32;
}

Conclusion

Arduino Programming Basics
- Minimum Program Structure
- Input, Output and Delays
C++ Programming Concepts
- Types and Variables
- Conditionals, Loops and Functions
Next Steps: Get your hands dirty!

This presentation is available online at:
http://nborko.github.io/arduino101/

All source files used for this workshop are available online at:
https://github.com/nborko/arduino101

Arduino 101Basic Programming Concepts

Agenda

Arduino Programming Basics

Arduino Programming Basics:

Arduino Program Structure

Arduino Programming Basics:

Arduino Program Structure

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Input and Output

Arduino Programming Basics:

Killing Time

Arduino Programming Basics:

Killing Time

C++ Programming Concepts

C++ Programming Concepts

Types and Variables

C++ Programming Concepts:

Types and Variables

C++ Programming Concepts:

Types and Variables

C++ Programming Concepts

Conditionals

C++ Programming Concepts

Conditionals

C++ Programming Concepts:

Conditionals

C++ Programming Concepts

Loops

C++ Programming Concepts

Loops

C++ Programming Concepts

Loops

C++ Programming Concepts

Loops

C++ Programming Concepts

Functions

C++ Programming Concepts

Functions

Conclusion

Arduino 101
Basic Programming Concepts