Sensors for the Lego Mindstorms NXT Robotics System
Lego Mindstorms Robotics
Sensors for the Lego Mindstorms NXT
I've been teaching kids robotics for a number of years in Maine and New Hampshire. I'm constantly impressed by the seemingly endless variations and capabilities of the Mindstorms platform. Not only is the number of machines, robots, devices and creations that can be constructed
The following is a review of all the sensors available for the Lego Mindstorms Robotics including official Lego products and sensors from third party manufacturers.
Lego Mindstorms Sound Sensor
The sound sensor measures relative sound levels in a percent scale - 0 to 100 with 0 being silence and 100 being the loudest sound in the environment. Often in my robotics classes the kids get confused about the function of the sound sensor. Its not some kind of intelligent spoken word to command device. Like you can't say "Move forward" and the robot would understand what you are saying, rather it's a simple switch that response to sound. You set the parameters such as "wait until the sound is above 50 percent" and then the robot will wait until it hears a loud sound before it does the next command. You can fool people into thinking it is responding to your words by shouting "Move" and then it will magically move but its only responding to the sound level and not the actual English word spoken.
The sound sensor was included in the original NXT kits but in newer Lego Mindstorms NXT 2.0 (8547) kits Lego has replaced the sound sensor with a second touch sensor and upgraded the light sensor to a more powerful color sensor.
So if you have the NXT 2.0 kit you could buy this sensor as another sensor to play with.
Mindstorms Light Sensor
This basic light sensor was included in the original NXT 1.0 release. The NXT 2.0 kit upgraded this sensor with a color sensor that also can be used as a basic light sensor.
The light sensor measures relative light levels on a scale from 0 - 100. It needs to be calibrated to the light levels in the room otherwise it will act differently when its moved from room to room.
Mindstorms Touch Sensor
The original NXT kit came with one touch sensor. The latest version, 2.0 comes with two touch sensors. The touch sensors can detect three things - push, release and bump which is a push and release. They can be used for all sorts of things like a push button, a wall detector or even a table edge.
Mindstorms Ultrasonic Detector
The Ultrasonic sensor looks like its two eyes but it doesn't see anything except for distance. Its a distance sensor for detecting obstacles, walls and objects. The way it works is sending out ultrasonic sounds and timing how long it takes for the sound to bounce off objects. Those "eyes" are really speakers with one working in the reverse as a microphone.
Just like a bat with echo location, with the Ultrasonic Sensor your Mindstorms robot can measure distance very accurately and up close to about two or three inches. When using multiple robots and Ultrasonic sensors the robot can be confused by multiple sounds bouncing around but for the most part the ultrasonic sensor is one of the most useful sensors for navigation. This sensor can be used to avoid walls for find openings in mazes.
Third Party Sensors
A great number of advance sensors are available from third party (non-Lego) manufacturers.
The Gyro Sensors from HiTechnic Products measure the additional dimension of rotation, the NXT Gyro Sensor returns the number of degrees per second of rotation as well as indicating the direction of rotation. You can build robots that that can balance, swing or perform other functions where measurement of rotation is essential.
Also from HiTechnic, the NXT Acceleration or Tilt Sensor measures acceleration in three axes. It also measures tilt along each axis.With this sensor you can build you can build self-leveling robots.
The NXT Compass Sensor is a digital compass that measures the earth's magnetic field and outputs a value representing the current heading. The magnetic heading is calculated to the nearest 1° and returned as a number from 0 to 359.
Mindsensors is another company that sells sensors for the NXT Mindstorms system. Their real clock sensor counts seconds, minutes, hours, date of the month, month, day of the week, and year with leap-year compensation which is handing for data logging applications.
Their NXTSumoEyes sensorcan detect obstacles in front-left, front-right or straight ahead which makes it perfect for NXT Sumo contests.
The Mindsensors Line Sensor Array makes line following robots more accurate by using an array of eight sensors. Using the light sensor that comes with the NXT you could only have four light sensors running but this has eight and they are very compact.
The Thermal Probe of the Mindstorms NXT can be used in data collection experiments and has a temperature operating range: -50C to 150C.
If you have an extremely complex robot you might need the Sensor Multiplexer which allows four sensors to be attached to a single sensor port.
Other sensors for the NXT are coming on the market and are available including GPS sensors, pressure sensors, flexible sensors and wireless sensors.