Download Arduino Android Blueprints by Marco Schwartz and Stefan Buttigieg easily in PDF format for free.

When directly comparing Arduino and Android, one can see that they are two incredibly different platforms with different targets. Arduino is mostly focused on connecting physical everyday objects to embedded microcontrollers. On the other hand, Android intends to provide the necessary operating system and framework to operate countless smartphones around the world. This reality also reflects the contrasting realities of the authors, who come from very different backgrounds and cultures;
Stefan hails from the Island of Malta, and he brings with him a medical background and passion for the intersection of technology and medicine, whereas Marco originates from France and has an electrical engineering background. The power of combining the efforts of Arduino and Android platforms bring about incredibly implemented practical projects that enhance daily life. Keeping this motivation in mind is what brought two authors from contrasting backgrounds together to work on this book. We believe in the intersection of technology and real life and visualize a future where technology will keep on forming an integral part of our day-to-day life.
What this book covers 

Chapter 1, Setting Up Your Workspace, covers the necessary steps that you will have to take in order to build all the projects of the book. You will learn how to set up the Android development environment. We will also build our first Arduino project. 

Chapter 2, Controlling an Arduino Board via Bluetooth, teaches us how to link Arduino and Android for the first time. We will build an Arduino system with a Bluetooth Low Energy module, and control a simple LED from an Android application.
Chapter 3, Bluetooth Weather Station, teaches us how to build our first useful application using Arduino and Android. We will build a weather measurement station, and visualize the measurements via an Android application, which we will build from scratch
Chapter 4, Wi-Fi Smart Power Plug, teaches us how to build a DIY version of a popular device: a wireless power switch. We will use an Android application to communicate with the switch via Wi-Fi, control it, and measure the energy consumption of the connected device.
Chapter 5, Wi-Fi Remote Security Camera, introduces a powerful Arduino board, the Arduino Yún, to build a DIY wireless security camera. We will also build an Android application to monitor this camera remotely from an Android phone.

Chapter 6, Android Phone Sensor, explains how to turn things around, and use the sensors from our phone to control the Arduino board. Applying this, we will use the gyroscope of the phone to control the angle of a servomotor.

Chapter 7, Voice-activated Arduino, teaches us how to use the powerful Android speech API to control an Arduino board via Bluetooth. 
Chapter 8, Control an Arduino Board via NFC, shows how to use the NFC chip present in many Android phones to activate a relay connected to an Arduino board.
Chapter 9, Bluetooth Low Energy Mobile Robot, uses everything we learned so far in the book to build a mobile robot based on the Arduino. The robot will be controlled via Wi-Fi from an Android application. 
Chapter 10, Pulse Rate Sensor, is dedicated to a medical application that measures the heart rate. We will connect a heart rate sensor to Arduino and monitor the measurements via Bluetooth Low Energy.