Arduino motion.pdf

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Arduino

A Quick-Start Guide

This PDF file contains pages extracted from Arduino , published by the Pragmatic

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visit http://www.pragprog.com .

Note: This extract contains some colored text (particularly in code listing). This

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content is otherwise identical.

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The Pragmatic Bookshelf

Dallas, Texas • Raleigh, North Carolina

It’s astonishing how quickly we get used to new technologies. A decade ago,

not many people would have imagined that we would use devices someday

to unobtrusively follow our movements. Today it’s absolutely normal for us

to physically turn our smartphones when we want to change from portrait to

landscape view. Even small children intuitively know how to use motion-

sensing controllers for video game consoles such as Nintendo’s Wii. You can

build your own motion-sensing devices using an Arduino, and in this chapter

you’ll learn how.

We’ll work with one of the most widespread motion-sensing devices: the

accelerometer . Accelerometers detect movement in all directions—they notice

if you move them up, down, forward, backward, to the left, or to the right.

Many popular gadgets such as the iPhone and the Nintendo Wii controllers

contain accelerometers. That’s why accelerometers are cheap.

Both fun and serious projects can benefit from accelerometers. When working

with your computer, you certainly think of projects such as game controllers

or other input control devices. But you can also use them when exercising

or to control a real-life marble maze. You can also use them to measure accel-

eration more or less indirectly, such as in a car.

You will learn how to interpret accelerometer data correctly and how to get

the most accurate results. Then you’ll use an accelerometer to build a motion-

sensing game controller, and you’ll implement a game that uses it.

6.1

What You Need

A half-size breadboard or—even better—an Arduino Prototyping shield

with a tiny breadboard

An ADXL335 accelerometer

A pushbutton

A 10kΩ resistor

Some wires

An Arduino board such as the Uno, Duemilanove, or Diecimila

A USB cable to connect the Arduino to your computer

A 6 pin 0.1" standard header

See Figure 50, All the parts you need in this chapter , on page 6 .

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6 •

Figure 50 — All the parts you need in this chapter

6.2

Wiring Up the Accelerometer

There are many different accelerometers, differing mainly in the number of

spacial axes they support (usually two or three). We use the ADXL335 from

Analog Devices—it’s easy to use and widely available. 1

In this section, we’ll connect the ADXL335 to the Arduino and create a small

demo program showing the raw data the sensor delivers. At that point, we

will have a quick look at the sensor’s specification and interpret the data.

In Figure 51, An ADXL335 sensor on a breakout board , on page 7 , you see

a breakout board containing an ADXL335 sensor on the right. The sensor is

the small black integrated circuit (IC), and the rest is just a carrier to allow

connections. On the top, you see a 6 pin 0.1" standard header. The sensor

has six connectors labeled GND, Z, Y, X, 3V, and TEST. To use the sensor on

a breadboard, solder the standard header to the connectors. This not only

makes it easier to attach the sensor to a breadboard but also stabilizes the

sensor, so it does not move accidentally. You can see the result on the left

side of the photo (note that the breakout board on the left is not the same as

on the right, but it’s very similar). Don’t worry if you’ve never soldered before.

In Section A1.2, Learning How to Solder , on page ? , you can learn how to

do it.

1. http://www.analog.com/en/sensors/inertial-sensors/adxl335/products/product.html

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Bringing Your Accelerometer to Life • 7

Figure 51 — An ADXL335 sensor on a breakout board

You can ignore the connector labeled TEST, and the meaning of the remaining

connectors should be obvious. To power the sensor, connect GND to the

Arduino’s ground pin and 3V to the Arduino’s 3.3 volts power supply. X, Y,

and Z will then deliver acceleration data for the x-, y-, and z-axes.

Like the TMP36 temperature sensor we used in Section 5.4, Increasing Preci-

sion Using a Temperature Sensor , on page ? , the ADXL335 is an analog device:

it delivers results as voltages that have to be converted into acceleration values.

So, the X, Y, and Z connectors have to be connected to three analog pins on

the Arduino. We connect Z to analog pin 0, Y to analog pin 1, and X to analog

pin 2 (see Figure 52, How to connect an ADXL335 sensor to an Arduino , on

page 8 , and double-check the pin labels on the breakout board you’re using!).

Now that we’ve connected the ADXL335 to the Arduino, let’s use it.

6.3

Bringing Your Accelerometer to Life

A pragmatic strategy to get familiar with a new device is to hook it up and

see what data it delivers. The following program reads input values for all

three axes and outputs them to the serial port:

Download Arduino_1_0/MotionSensor/SensorTest/SensorTest.ino

const unsigned int X_AXIS_PIN = 2;

const unsigned int Y_AXIS_PIN = 1;

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