Arduino is best described as a single-board computer that is deliberately designed to be used by people who are not experts in electronics, engineering, or programming. It is inexpensive, cross-platform (the Arduino software runs on Windows, Mac OS X, and Linux), and easy to program. Both Arduino hardware and software are open source and extensible.

Arduino is also powerful: despite its compact size, it has about as much computing muscle as one of the original navigation computers from the Apollo program, at about 1/35,000 the price.

Programmers, designers, do-it-yourselfers, and artists around the world take advantage of Arduino’s power and simplicity to create all sorts of innovative devices, including interactive sensors, artwork, and toys.

We built each of the products in this book using the Arduino Uno (Figure 1-1 and Figure 1-2), which, at the time of writing, is the latest model. By the time you’re reading this, there may be something newer.

You don’t have to know Arduino Uno’s technical specifications to build and program the gadgets in this book, but if you’re interested, you can find them at the official Arduino website.

Figure 1-1. Front of the Arduino Uno (Rev. 3).

Figure 1-2. Back of the Arduino Uno.

An electronic circuit is, as the term implies, electricity moving in a path very much like a circle. Each circuit has a beginning, a middle, and an end (which is usually very close to where it began). Somewhere in the middle, the circuit often runs through various electronic components that modify the electrical current in some way.

Each device in this book is a circuit that combines Arduino with different electronic components. Some of these manage the power and path of the electricity, others sense certain conditions in the environment, and still others display output about those conditions.

Let’s take a look at some of the components we will be using in our circuits:

We order most of our electronics components from these online retailers:

Maker Shed, from MAKE and O’Reilly Media, sells books, kits, and tools, as well as many of the components needed to build the projects in this book including Arduino, breadboards, sensors, and basic electronic components. Maker Shed also supplies convenient bundles for many of the projects in this book (you can find more information about these bundles in the individual project chapters).

Don’t count out your friendly local RadioShack, though. While writing this book, more than once we ran out to RadioShack for a last-minute component.

For years RadioShack cut back on its electronic components inventory, apparently seeing a better future for the business by featuring cell phones and other consumer electronics. But the company has recently begun to embrace the maker movement; at the time of writing, most of their stores around the country are even carrying Arduinos. We’re hopeful RadioShack is on the return path to being the hacker heaven it was years ago.

A computer program is a coded series of instructions that tells the computer what to do. The programs that run on Arduino are called sketches.

The sketches used in this book mostly tell Arduino to read data from one of the pins, such as the one connected to a sensor, and to write information to a different pin, such as the pin connected to an LED or display unit.

Sometimes the sketches also instruct Arduino to process that information in a certain way: to combine data streams, or compare the input with some reference, or even place the data into a readable format.

An Arduino program has two parts: setup() and loop().

By long tradition (going back to 2006), the first Arduino sketch you will write is to make an LED blink.

Arduino pins can be used for input and output, as long as you tell the computer which is which. So in this sketch, we tell the Arduino to set pin 13 to be the LED OUTPUT pin, and then we alternately send electricity to pin 13 (setting the pin HIGH) and cut off the electricity to pin 13 (setting the pin LOW). With each alternation, the LED turns on and off.

We’ll write all the sketches in this book using the Arduino integrated development environment (IDE), which, simply put, is special software for writing and uploading code to Arduino.

Breadboard the Circuit

The circuit portion of this project is very simple: take an LED and place the long lead into pin 13 on Arduino, as you can see in the Figure 1-4 breadboard view.

Figure 1-3. The Arduino IDE on a Mac.

Figure 1-4. LED long lead inserted into pin 13 on the Arduino (image made with Fritzing).

/*
  Blink
  Turns on an LED for one second,
  then off for one second, repeatedly.
  This example code is based on example code
  that is in the public domain.
*/

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

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
}