NXT: Sensors and Actuators

Sensors and actuators can be connected to the NXT controller through the four input ports and three output ports:

In the following we describe the different kind of LEGO sensors and actuators that can be connected to the NXT, the connection cables needed, the internals of the input and output ports, and how sensors and actuators can be accessed through methods in the Java classes of leJOS NXJ.

Sensors

The NXT controller has four input ports labeled 1, 2, 3 and 4, Figure 1. Sensors can be connected to the NXT through these input ports. The LEGO sensors can be divided into two categories of sensors: NXT sensors and RCX sensors. These two classes of sensors are physically connected to the input ports in two different ways.

Figure 1 The four NXT Input Ports.

NXT Sensors

At present there are four NXT sensors available from LEGO: Light sensor, ultrasonic sensor, touch sensor and sound sensor, Figure 2. These are all connected to the input ports by means of the NXT cable, a six wire cable with RJ16 connectors in both ends, Figure 3.

Figure 2 Four different NXT sensors.

Figure 3 An NXT cable, picture from Custom NXT Cables.

RCX Sensors

There are five different RCX sensors available from LEGO: Light, temperature, angle and two touch sensors, Figure 4. These sensors were developed for the RCX and they all use a two wire cable with 2x2 el-plate connectors in both ends for connection to the RCX input ports. To connect these sensors to the NXT the converter cable as shown in Figure 5 is needed.

Figure 4 The five RCX sensors.
The leJOS Tutorial, (1.2.2006),
Controlling the Hardware: Sensors.

Figure 5 The LEGO 8528 conversion cable.

Input ports

Figure 6 An NXT input port, Hardware Developer Kit, p.6.

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Actuators

The NXT controller has three output ports labeled A, B and C. Actuators can be connected to the NXT through these output ports. Just as with the LEGO sensors the LEGO actuators can be divided into two categories of actuators: NXT actuators and RCX actuators. These two classes of actuators are physically connected to the output ports in two different ways.

NXT Actuators

At present there is one NXT actuator available from LEGO: a motor, Figure 7. NXT motors are connected to the output ports by means of the NXT cable of Figure 3.

Figure 7 Philippe Hurbain, LegoŽ 9V Technic Motors compared characteristics,
(18.9.2007), contains photos, circuit diagrams and detailed operation of the NXT motor.

RCX Actuators

There are several types of RCX actuators available from LEGO: lamps and motors, Figure 8 and 9. These actuators were all developed for the RCX and as the RCX sensors they use a two wire cable with 2x2 el-plate connectors in both ends for connection to the RCX output ports. To connect these actuators to the NXT the converter cable as shown in Figure 5 is needed.

Figure 8 Two LEGO lamps.

Figure 9 Philippe Hurbain, LegoŽ 9V Technic Motors compared characteristics, (18.9.2007), contains photos, circuit
diagrams and detailed operation of the different motors.

Each motor has its own characteristics with respect to power consumption, rotations per minut etc. Philippe Hurbaine has made a very detailed investigations of LEGO motors including the NXT motor.

Output ports

Figure 6 An NXT output port, Hardware Developer Kit, p.5.

References

Hardware Developer Kit

Philippe Hurbain, Custom NXT Cables

Philippe Hurbain, LegoŽ 9V Technic Motors compared characteristics

Last update: 18-09-07