====== Angle & Orientation Sensors ======
{{:en:iot-open:czapka_b.png?50| General audience classification icon }}{{:en:iot-open:czapka_e.png?50| General audience classification icon }}\\
== The Inertial Measurement Unit (IMU) ==

An IMU is an electronic device that consists of an accelerometer, gyroscope, and sometimes a magnetometer. The combination of these sensors returns the object's orientation in 3D space. IMU sensors can present the object's current position and movement, expressed with at most six values called the DOF (Degrees Of Freedom). Three values represent the linear movements that the accelerometer can measure:
  * moving forward/backwards,
  * moving left/right,
  * moving up/down.
Another three values present the rotation in three axes that can be measured by gyroscope:
  * roll side to side,
  * pitch forward and backwards,
  * yaw left and right.

A **gyroscope** is a sensor that measures the angular velocity. A microelectromechanical system (MEMS) technology integrates the sensor into the chip. The sensor output can be analogue or digital, using I2C or SPI interface. Gyroscope microchips can vary in the number of axes they can measure. The available number of axes is 1, 2 or 3 axes in the gyroscope. A gyroscope is commonly used with an accelerometer to determine the device's orientation, position and velocity precisely.
Gyroscope sensors are used in aviation, navigation and motion control.

An **accelerometer** measures the acceleration of the object. The sensor uses microelectromechanical system (MEMS) technology, where capacitive plates are attached to springs. When acceleration force is applied to the plates, the capacitance is changed; thus, it can be measured. Accelerometers can have 1 to 3 axes. The 3-axis accelerometer can detect the device's orientation, shake, tap, double tap, fall, tilt, motion, positioning, shock or vibration. Outputs of the sensor are usually digital interfaces like I2C or SPI. The accelerometer is often used with a gyroscope to measure the object's movement and orientation in space precisely.\\
Accelerometers measure objects' vibrations, including cars, industrial devices, and buildings, and detect volcanic activity. IoT applications can also be used for accurate motion detection for medical and home appliances, portable navigation devices, augmented reality, smartphones and tablets.

A **magnetometer** is a sensor that can measure the device's orientation to the Earth's magnetic field. A magnetometer is used as a compass in outdoor navigation for mobile devices, robots, and quadcopters.

Different elements allow measuring linear accelerations, angular accelerations, and magnetic fields in three axes. There exist elements that combine two (called 6-axis or 6-DOF) or all (9-axis, 9-DOF) measurement units. Popular integrated circuits are MPU6050 (3-axes gyro + 3-axes accelerometer, figure {{ref>imu6050}}), MPU9250 (3-axes gyro + 3-axes accelerometer + 3-axes compass, figure {{ref>imu9250}}), and BNO055 (3-axes gyro + 3-axes accelerometer + 3-axes magnetometer, figure {{ref>bno055}}). All of them can be programmed in an Arduino environment using dedicated libraries. 
\\ The latter automatically calculates additional information like gravity vector and absolute orientation expressed as an Euler vector or a quaternion. The sample connection circuit for the BNO055 sensor is present in figure {{ref>bno055_2}}. Note, figure {{ref>bno055_2}} does not present pull-up resistors on the I2C bus as they are integrated into the development boards.

<figure imu6050>
{{ :en:iot-open:hardware2:20230925_114148_-_kopia.jpg?300 | IMU MPU6050 module}}
<caption>IMU MPU6050 module</caption>
</figure>

<figure imu9250>
{{ :en:iot-open:hardware2:20230925_114235_-_kopia.jpg?300 | IMU MPU9250 module}}
<caption>IMU MPU9250 module</caption>
</figure>

<figure bno055>
{{ :en:iot-open:getting_familiar_with_your_hardware_rtu_itmo_sut:arduino_and_arduino_101_intel_curie:imu_c.jpg?200 | IMU BNO055 module}}
<caption>IMU BNO055 module</caption>
</figure>

<figure bno055_2>
{{ :en:iot-open:getting_familiar_with_your_hardware_rtu_itmo_sut:arduino_and_arduino_101_intel_curie:imu_sch_hd.jpg?400 | Arduino Uno and IMU BNO055 module schematics}}
<caption>Arduino Uno and IMU BNO055 module schematics</caption>
</figure>

The example code:
<code c>
//Library for I2C communication
#include <Wire.h>
//Downloaded from https://github.com/adafruit/Adafruit_Sensor
#include <Adafruit_Sensor.h>
//Downloaded from https://github.com/adafruit/Adafruit_BNO055 
#include <Adafruit_BNO055.h>
#include <utility/imumaths.h>
Adafruit_BNO055 bno = Adafruit_BNO055(55);
void setup(void)
{
  bno.setExtCrystalUse(true);
}
void loop(void)
{
  //Read sensor data
  sensors_event_t event;
  bno.getEvent(&event);
  //Print X, Y And Z orientation
  Serial.print("X: ");
  Serial.print(event.orientation.x, 4);
  Serial.print("\tY: ");
  Serial.print(event.orientation.y, 4);
  Serial.print("\tZ: ");
  Serial.print(event.orientation.z, 4);
  Serial.println("");
  delay(100);
}

</code>

<note important>Most MEMS devices present built-in inaccuracy. For this reason, gyros and accelerometers should be calibrated before use to calculate their so-called offset, an average error they present (in each axis separately). Later, this error is used to calculate a correction factor applied during regular operation. Sample MPU6050 library along with calibration code can be found in the Github repository ((https://github.com/ElectronicCats/mpu6050/tree/master)).</note>
<note important>Similar problem is present in the case of the magnetometers: the surrounding environment can impact readings; thus, they require calibration that can be achieved by recording the minimum and maximum values during rotation in every axis. This process is common when using a drone in a new location.</note>