Whats inside the NXT Brick: Part III

Today is part three of Whats inside the NXT Brick series. Today's article will focus on the sensor ports, how they work, and the three different types of sensors.

The NXT features four sensor ports. Thats one extra port compared to the RCX's three input ports. These ports are based on the same six pin/wire design as the motor ports. However, the use of the wires is a little different...

Sensor Port Layouts
The following drawing shows the layout of the input ports.

The first ANA pin is connected to the avr processor and the current generator. What this means is that the ports can generate the power needed to run the old RCX sensors from this wire. The second and third pins are simple ground wires. Nothing too special about them. The fourth pin, IPOWERA is the wire responsible for powering the NXT sensors. Pins five and six are responsible for doing the heavy duty work with the sensors. Both of these pins are connected to the ARM7 processor and are the ones responsible for taking the signals from the sensor and delivering them to the NXT for diagnosing.

Sensor TypesThere are three different types of sensors in the Mindstorms NXT Robotics set.

The first type is the active sensor. This type of sensor requires a constant supply of power to continouously measure the sensor's level. They also require a specific power to measurement timing. This special timing is achieved by powering the sensor for 3 milliseconds and then measuring the results for .1 milliseconds. This process is repeated constantly. There are only two types of sensors that are active sensors, both of which are found in the old RIS kit: the light sensor and rotation sensor.


Passive sensors on the other hand do not require any specific power/time measurement. The measurements that they take are refreshed every 3 milliseconds because the timing has to be the same as the active sensor setup. Passive sensors include: touch sensors for both the RIS and NXT, light sensor in the NXT, sound sensor, and the temperature sensor.

The digital sensor is the newest addition to the LEGO sensors. There is only one sensor that is in this catagory: the new ultrasonic sensor. The reason that they are called digital sensors is because on these new types an external chip on the sensor is used to process the data that is being sampled.

Thats all for tonight, check back tomorrow!