Raspberry Pi: Sense Hat

Summary

This documentation deals with the Raspberry Sense Hat.

Requirements

• Hardware: Raspberry Pi
• Operating system: Rasbian
• Interpreter: Python or Python3
• Packages: sense-hat

Description

This add-on board has a is packed with three sensor chips as wall as a 8 by 8 RGB Led matrix and a joystick. The Sensors are a barometer, a hygrometer and an IMU (Inertial Measurement Unit). The barometer measures the air pressure and the temperature. The hygrometer measures the humidity and the temperature as well. The used IMU holds a gyroscope, an accelerometer and a magnetometer for an accurate determination of rotation, movement and detection of magnetic fields.

Package Installation

sudo apt-get install sense-hat

Python Programming

The Sense Hat is mainly used via python programming. The developers also developed a sense hat programming simulation program on trinket.io where you are able to test your code without owning the Sense Hat.

The Project comes with two main libraries the sense_emu which is needed when using the Emulator and the sense_hat for the device. For detailed information about the library use the documentation.

Importing the Libary

# emulator libary
from sense_emu import SenseHat
sense = SenseHat()

# sensehat libary
from sense_hat import SenseHat
sense = SenseHat()

Using the barometer

The barometer delivers two functions the get_pressure() and the get_temperature_from_pressure().Both of them return a float value of the corresponding unit.

pressure = sense.get_pressure()
print("Pressure: %s Millibars" % pressure)

temp = sense.get_temperature_from_pressure()
print("Temperature from pressure sensor: %s C" % temp)

Using the hygrometer

The hygrometer delivers also two functions the get_humidity() and the get_temperature_from_humidity(), Both of them return a float value of the corresponding unit.

humidity = sense.get_humidity()
print("Humidity: %s %%" % humidity)

temp = sense.get_temperature_from_humidity()
print("Temperature from pressure humidity: %s C" % temp)

Using the Inertial Measurement Unit

The separte measurement units have their own functions the returns a preformatted dictionary object. The library also delivers a raw funtion that returns unformatted values for the maximum flexibility at after processing

Using the Gyroscope

The get_gyroscope() function returns a dictionary object with the pitch, roll, yaw measured in degrees. The raw output function get_gyroscope_raw() returns a dictionary object with the x, y, z axis representing the rotational intensity of the axis in radians per second.

These three rotation axis can determine the exect headed direction in the three-dimensional space. The three axis are used like in the image below.

gyroscope = sense.get_gyroscope() degrees
print("p: {pitch}, r: {roll}, y: {yaw}".format(**gyroscope))

# Returned dictionary object
{
  "pitch": Float,
  "roll": Float,
  "yaw": Float
}

gyroscope_raw = sense.get_gyroscope_raw()  radians per second
print("x: {x}, y: {y}, z: {z}".format(**gyroscope_raw))

# Returned dictionary object
{
  "x": Float,
  "y": Float,
  "z": Float
}

Used Hardware

Raspberry Pi 3 Model B+

Raspberry Pi Sense Hat

References

• https://projects.raspberrypi.org/en/projects/getting-started-with-the-sense-hat
• https://pythonhosted.org/sense-hat/api/#sense-hat-api-reference
• https://trinket.io/sense-hat