A **sensor node**, also known as a **mote**, is a node in a sensor network that is capable of performing some processing, gathering sensory information and communicating with other connected nodes in the network.
The main components of a sensor node are a **microcontroller**, **transceiver/Communication Module**, **memory**, **power source** and one or more **sensors.**
A basic IMU (Intertial Measurement Unit) generally provides raw sensor data, whereas an AHRS takes this data one step further, converting it into heading or direction in degrees, converting the raw altitude data into standard units like feet or meters, etc.
An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch and yaw. These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity) sensors and consist of either solid-state or microelectromechanical systems (MEMS) gyroscopes, accelerometers and magnetometers. They are designed to replace traditional mechanical gyroscopic flight instruments.
Adafruit's 10DOF https://en.wikipedia.org/wiki/Degrees_of_freedom[(10 Degrees of Freedom)] breakout board allows you to capture ten distinct types of motion or orientation related data.
- open up the Serial Monitor (Tools > Serial Monitor),
- set the baud rate to 115200
.output
image:./sensors_01_AHRSOutput.png[alt="AHRS raw data"]
This raw data shows the main orientation data, consisting of 'roll', 'pitch' and 'heading' (or 'yaw) in degrees, followed by the current altitude and temperature
The AHRS sketchs reads raw data from the board's accelerometer/magnetometer and converts the raw data into easy to understand **Euler angles.**
In this case, we can see that the **roll is about 18°**, the **pitch is about 78°** and the **heading or yaw is about 32°**, and the sketch will keep updating itself with the latest values at whatever speed we've set in the sketch.
.Euler angles, one of the possible ways to describe an orientation
image:./Eulerangles.svg.png[alt="Euler angles"]
The first attempt to represent an orientation is attributed to Leonhard Euler. He imagined three reference frames that could rotate one around the other, and realized that by starting with a fixed reference frame and performing three rotations, he could get any other reference frame in the space (using two rotations to fix the vertical axis and other to fix the other two axes). The values of these three rotations are called Euler angles.
.Tait–Bryan angles, another way to describe orientation
These are three angles, also known as yaw, pitch and roll, Navigation angles and Cardan angles. Mathematically they constitute a set of six possibilities inside the twelve possible sets of Euler angles, the ordering being the one best used for describing the orientation of a vehicle such as an airplane. In aerospace engineering they are usually referred to as Euler angles.
