Pablo Software Solutions
Extreme Mindstorms: An Advanced Guide to Lego Mindstorms RCX by Dave Baum, Michael Gasperi, Ralph Hempel and Luis Villa. It has information about programming the RCX in NQC, Forth, and using legOS, but most importantly it has two whole chapters that I wrote on Building Homebrew Sensors. These chapters take the time to go through the construction process step-by-step in easy to follow instructions. Click the box to find out more about the book and how to purchase it online.
Extreme NXT, Taking your NXT to the next level:  LEGO Mindstorms NXT is an outstanding new product that allows anyone to build complex inventions, but there are limits to what you can do with what comes inside the box.  This book shows you how to think outside the box and extend the NXT to the next level.  With more than twenty-five exciting projects that range from a simple light switch to a cool magic wand that writes words in thin air.  The projects are explained with easy step-by-step instructions, and whether you are a novice or an expert you will be able to successfully construct them.  A tutorial on breadboard construction and soldering is also included.
New sensors like color, pressure, magnetism, and even the wind are covered along with games like surfing, Pong, and Simon.  On the serious side, there are classic engineering challenges like controlling an inverted pendulum, making a robot that follows a wall, and building a light seeking vehicle.  Some projects are fun like the fusion of the NXT and an Etch-A-Sketch called the Etch-A-NXT.  Other projects are useful like a motorized camera mount that takes 360 degree photographs, or a NXT version of the classic Clapper remote control.  Details are presented for practically unlimited expansion of the NXT inputs and outputs by using the I2C communications bus, and several power amplifier designs allow the NXT outputs to drive bigger motors.
So, if you are looking for the next thing to do with your NXT, this is the book for you.  If you are involved in robotics, engineering, science, electronics, or just having fun, there is an interesting project in here for you.
The next generation of robots! Create the smartest, strongest and most advanced LEGO® robot ever, in as few as 30 minutes! The new NXT Intelligent Brick, your robot's "brain," features a powerful 32-bit microprocessor and more memory, plus support for USB 2.0, Bluetooth and more! A highly versatile palette of LEGO TECHNIC® elements combines with state-of-the-art ultrasonic, sound, light and touch sensors in the next generation of intuitive robotics. With included Quick-Start guide, easy-to-use software and step-by-step building instructions, beginners and experts alike can create humanoid, vehicle and animal robots that obey every command! Improved light sensors can detect different colors and intensities, while the new sound sensor enables robots to respond to sound patterns and tones. Robots can really "feel" with improved touch sensors, while ultrasonic "eyes" measure distance and movement. Programming software is now available for both PC and Macintosh, plus with Bluetooth support, you can even command your robot from your mobile phone! LEGO® MINDSTORMS® NXT Includes: All-new NXT Intelligent Brick with 32-bit microprocessor, more memory and FLASH 3 Interactive Servo motors feature built-in rotation sensors to align speed for precise control New sound sensor reacts to sound commands, patterns and tones New ultrasonic visual sensor responds to movement Improved touch sensor reacts to touch and release Improved light sensor detects different colors and light intensities 519 specially selected LEGO TECHNIC elements for sturdy and durable building and improved functionality and movement 4 input ports, 3 output ports and 7 6-wire cords Matrix display Real sound speaker USB 2.0 and Bluetooth support Easy-to-use PC and Mac compatible interface Intuitive, icon-based drag-and-drop program "building" environment 6 AA batteries required (not included).
Here are video previews of a few projects in the Extreme NXT book
Extreme NXT Table Of Contents

CHAPTER 1 In the Beginning
  The RCX and the Robotics Invention System
  The MINDSTORMS NXT
CHAPTER 2 In the Box
  The Sensors
  The Motors
  The Lamp
  The Languages
CHAPTER 3 Connecting to the NXT
  NXT Ports
  Sensor Input Pinout and Signal Description
  Motor Output Pinout
  Physically Connecting to the NXT
  Making Your Connectors
  Screw Terminal for Passive Sensors
  RCX Compatibility Cable
CHAPTER 4 Contact Sensors
  Touching Wires
  Electronic Surfboard
  Switches
  Parallel and Series
  Antenna Sensor
CHAPTER 5 Resistive Sensors
  Analog to Digital Conversion
  Ohmmeter Program
  Measuring Salinity
  Homebrew Temperature Sensor
  NXT Digital Thermometer
  Relative Humidity Sensor
  Light Sensor
  Comparison of LEGO and CdS Light Sensor
  Theremin
  Braitenberg Vehicle 2
  Two Switch Input
CHAPTER 6 Potentiometer Sensors
  Resistance Selection
  NXT Protractor
  Pressure Sensor
  Broom Balancer
  Bottom Mounted Joystick
  Top Mounted Joystick for the T-56
CHAPTER 7 Voltage Sensors
  Design of a -5V to +5V Sensor
  NXT Battery Tester
  A -15V to +15V Sensor
CHAPTER 8 4.3V Powered Sensors
  Hall Effect Sensor
  Robot Mouse
  Transistor Buffer
  Infrared Rangefinder
  Wall Follower
  Differential Light Sensor
  Digital Sundial
  Enhancing the Transistor Buffer
CHAPTER 9 Two-Wire Powered Sensors
  Signals
  Programming
  NXT-G
  NBC
  Half-Volt Sensor
  Current Sensor
  Electronic Whistler
  Pressure Sensor
CHAPTER 10 Aftermarket Vendors
  HiTechnic
  Mindsensors.com
  Techno-Stuff
  Vernier and DCP Microdevelopments
  LEGO Education
CHAPTER 11 NXT Motor Interfaces
  The Clapper
  The Etch-A-NXT
  The Pneumatic Gripper
CHAPTER 12 Beyond NXT Motors
  The Motor Block
  Output Control Program
  Lamps
  Muscle Wires
  Electromagnets and Solenoids
  Kinetic Sculpture
  Relays
  Doubling Outputs
  Light Emitting Diodes
  More Power
  One MOSFET Amplifier
  Bipolar MOSFET Amplifier
CHAPTER 13 I2C Bus Communication
  I2C Communications
  PCF8574
  Eight Outs
  Magic Wand
  Four Ins and Outs
  Simon Game
  Relay Outputs
  PCF8591
  Four Analog Ins
  Color Sensor
  Going Further
CHAPTER 14 Cool Combinations
  Data Logging
  NXT-to-NXT Bluetooth Remote Control
  LEGO Train Station
  Panoramic Camera
  Graphics
  NXT Pong Video Game
  Remotely Guided Vehicle
APPENDIX A Breadboard Construction Technique
  Solderless Breadboard
  Building on the Breadboard
  Soldering
  Building a Printed Circuit Board
Appendix B References, Links, and Sources
APPENDIX C Code Listings
Extreme NXT
Return to my main LEGO MINDSTORMS Sensor Input page
Click here to download Extreme NXT Errata
Click here to download Source Code
Click here to see the updated Appendix B References, Links, and Sources