In order to operate properly with the
Lego Mindstorms NXT, it is necessary to know what
components are in the box.
Sensors are devices that provide feedback
to the system such as the location and performance. The
NXT has the following main sensors
A printed circuit board (PCB) mounted
push button and a connector.
The light sensor includes a light
emitting diode (LED) light source that can be tuned on
and off from software. This allows to measure either the
reflected LED light shining back from an object or the
ambient light falling on the sensor. Basically, the
package contains the LED, phototransistor, and connector
mounted on the top of the PCB.
The sound sensor includes a microphone
mounted in a plastic foam, a capacitor, and the
connector on the top of the PCB in addition to an
The objectives of this sensor is avoiding
objects. The guts of the sensor are shown in the
following figure. The two cylindrical objects connected
with wires to the PCB are the ultrasonic speaker and
microphone. This sensor has its own microprocessor,
accordingly, it reports distance in absolute units
rather than on some relative scale like the other
sensors. Its operation is similar to SONAR system. It
transmits a short burst of ultrasonic sound at 40 kHz.
It then measures the time it takes for the sound to
travel out to an object, reflect, and travel back.
The rotation sensor resolves 16 locations
per rotation of 22.5 degrees. It detects the vanes on a
rotating shaft with two opto-interrupters. An
interrupter is a phototransistor and an LED that are
pointed at each other with a small gap in between. The
NXT watches the states of the two interrupters to
determine which direction the sensor is rotating.
The NXT motor is a combination of gear
reduction and feedback sensing. The gear reduction
involves eight different gears.
NXT-G is the programming language of the
Lego Mindstorms NXT. The language is mostly graphical,
consisting of blocks that perform operations such as
input, output, computation, and execution flow.