Sensors and accessories can greatly expand the capabilities of a robot. In this article, from the series dedicated to the Lego Mindstorms NXT, platform we will review some of these devices available from Lego and third party certified manufacturers. For most of these devices support is available in the programming environments used to work with the NXT, in Microsoft RDS predefined services are included with the package, while in NXT-G most of the predefined programming blocks have actions designed for certain types of sensor, however creating custom services or blocks for certain sensors or devices is possible. Besides Lego’s own hardware, certified devices are available from HiTechnic and Mindsensors and support is also provided by the respective manufacturers.
1. Lego additional hardware
Various devices are available at the Lego Shop website for prices not exceeding 60 US dollars.
Accelerometer sensor (2852724) – This sensor is a 3-axis accelerometer with the aid of which you can determine tilt conditions and acceleration forces.
IR receiver (2855040) – The IR receiver enables your robot to receive commands from 8879 or 8885 Lego remote controls and, depending on programming, you can command your robot to perform certain tasks or directly control it.
IR remote control (8879) – The device enables you to remotely control your robot through infrared communication, providing control for a number of functions. It has 4 control channels, jog wheels, stop and direction control switches. It requires separate power from 3 AAA type batteries.
IR seeker sensor (2852725) – The sensor can be used to detect and follow IR right sources thanks to its array of 5 IR detectors arranged at 60 degree angles with respect to each other
Gyroscopic sensor (2852726) – The single axis gyro can be used to detect rotation of the robot.
Compass sensor (10285) – The integrated magnetic compass can measure the Earth’s magnetic field and output the magnetic heading in order to determine what direction your robot is facing.
Color sensor (9694) – This sensor is included with the 9547 Mindstorms NXT kit but not with the 9527. It can measure ambient and reflected light intensity and can discriminate between 6 different colors. It’s integrated light source can emit light in 3 different colors.
2. HiTechnic devices
Hardware provided by HiTechnic is certified by Lego and you can find these devices on the HiTechnic products page.
Angle sensor (NAA1030) – This device can be mounted onto any axle in your build to measure axle position and rotation speed. The encoder provides 360 degree position determination with 1 degree precision.
Acceleration/tilt sensor (NAC1040) – The 3-axis accelerometer can measure tilt and acceleration forces up to 2G in each direction.
Barometric sensor (NBR1036) – This interesting sensor can measure atmospheric pressure and temperature with precisions up to 0,025 mmHg barometric pressure and a 0,1 degrees Celsius respectively. The sensor outputs its pressure measurements in inHg or hPa and temperature in Celsius or Fahrenheit. Once calibrated to a certain location it can also provide pretty accurate altitude readings.
Color sensor V2 (NCO1038) – This sensor can discriminate between a range of more than 15 colors or more and features an improved detection range.
EOPD sensor (NEO1048) – The Electro-Optical Proximity Detector can be used to detect objects and distance with the aid of an internal light source. Thanks to this it also reduces detection errors, effectively filtering out ambient light and can make accurate readings up to 20 cm distance.
Gyro sensor (NGY1044) – The sensor measures the rotation of your robot as well as the direction with a speed up to 360 degrees per second.
IRLink sensor (NIL1046) – This sensor is an IR transceiver that can be used to read data and control other Lego IR hardware.
IR receiver sensor (NIR) – With the aid of this IR sensor you can control your robot with the 8879 or 8885 remote controls from Lego.
PIR sensor (NIS1070) – This pyroelectric sensor can be used to detect moving persons or animals, similar to sensors found in security systems.
IR seeker sensor V2 (NSK1042) – Similar in construction to the Lego IR seeker sensor the upgraded device can also detect modulated IR signals, making it adequate for using it in robot soccer competitions.
Rotacaster wheel (HRC2148) – This wheel type us useful for creating omnidirectional robots as it allows forward, backward and sideways motions.
Sensor multiplexer (NSX2020) – With the aid of this module you can connect 4 sensors to 1 NXT port, greatly expanding your robot’s sensing abilities, however with some limitations in the case of sensors which support write operation (e.g. light sensor predefined mode). It comes with it’s own 9V power source to support the extra sensors. Programming support for this device is also available at HiTechnic or on online communities.
3. Mindsensors devices
Sensors and accessories available from Mindsensors website are more complex and require a certain amount of skills to implement, however support for multiple programming environments, including the NXT-G, is provided. Most expensive hardware does not exceed prices of around 150 US dollars.
Vision Subsystem V4 (NXTCam-V4) – This sensor does realtime image processing to discriminate between 8 colors, measuring at a rate of 30 fps. Lens focus can be adjusted and it can also be connected directly to a USB interface.
Touch Panel for NXT – The Mindsensors touch panel can be mounted directly over the NXT brick display and can be used for gesture recognition and different commands that can be accessed by using the 8 virtual buttons on the sides.
IR obstacle detector (NXTSumoEyes-V2) – This sensors features 3 detection areas and can detect objects up to 30 cm distance. It features 2 detection ranges, short range – up to 15 cm and long range up to 30 cm.
High precision IR distance sensors, long range, medium range and short range (DIST-Nx-Long-V3, DIST-Nx-Medium-V3, DIST-Nx-Short-V3) – These high resolution sensors can provide accurate distance measurements in millimeters and come in three detection range flavors: long range – 30 to 150 cm, medium range – 10 to 80 cm and short range – 6 to 30 cm.
AbsoluteIMU-AC – This unit is an Inertial Measurement Unit (IMU) and features integrated accelerometer and compass sensors. It has resolution of 1 degree for tilt and magnetic compass, accelerometer resolution of 10 mg and selectable sensitivity of 2, 4, 8 or 16g.
Motor multiplexer (NXTMMX-V2) – This module allows connecting two motors on a single port on your NXT. It also features a pass-through port for connecting additional sensors or multimplexor and has an external power supply connection for powering additional hardware.
Various multiplexers – allow for connecting 3 touch sensors on one single port or I2C devices.
4. Dexter Industries modules
Interesting modules are available at Dexter Industries website and support for different programming environments is also provided.
WiFi sensor – Enables wireless network communication of your NXT, creating numerous control and data acquisition possibilities. The WiFi interface is compatible with 802.11 b/g/n standards.
dIMU inertial sensor – Features a 3-axis accelerometer and gyroscope in the same unit with measurement levels of 2, 4 and 8g for the accelerometer and 250, 500 and 2000 degrees per secong measuring ability of the gyro.
dGPS module – This enables your robot to navigate using the GPS system. Depending on programming, the robot can navigate freely and determine position or navigate from predetermined coordinate locations.