Sense Hat Raspberry Pi Zero
This example shows you how to read the sensor values, read the position of joystick and control the LED Matrix on Raspberry Pi™ Sense HAT using MATLAB™ Support Package for Raspberry Pi Hardware.
Introduction
Note: The Raspberry Pi Sense HAT is compatible with the Raspberry Pi 3, Raspberry Pi 2, Model B+, and Model A+, but NOT the earlier 26-pin models of Raspberry Pi 1 Model B & A's. Pi not included! This forum post mentions getting the sense hat to work with the Pi Zero and older versions of the Raspbian software, but it looks like this has. The Sense HAT, which is a fundamental part of the Astro Pi mission, allows your Raspberry Pi to sense the world around it. In this project, you will learn how to control the Sense HAT’s LED matrix and collect sensor data, and you will combine these ideas in a number of small projects. Raspberry Pi Zero W. Single-board computer with wireless and Bluetooth connectivity. The Sense HAT is an add-on board for Raspberry Pi.
The Raspberry Pi Sense HAT is an add-on board that includes an 8X8 RGB LED matrix, a five-position joystick and the following sensors:
Humidity sensor
Pressure sensor
IMU sensor (Accelerometer, Gyroscope, and Magnetometer).
In this example you will learn how to create a sensehat object to connect to the Raspberry Pi Sense HAT, read sensor values, read the position of the joystick and control the LED matrix.
Prerequisites
We recommend completing Getting Started with MATLAB Support Package for Raspberry Pi Hardware example
Required Hardware
To run this example you will need the following hardware:
Connect Sense HAT
Attach the Sense HAT to the Raspberry Pi expansion header. Make sure that you power down your Raspberry Pi before attempting to attach the Sense HAT.
Create a Sense HAT object
Create a Sense HAT object by executing the following on the MATLAB prompt.
mysensehat is a handle to a sensehat object.
Let us read the temperature from Sense HAT.
Reading Environmental Sensors
Sense HAT includes humidity and pressure sensors which measure the temperature, the pressure and the humidity. Let's read the value of humidity and pressure measured by these sensors.
Temperature can be read from either the humidity sensor or the pressure sensor. To read the temperature from the humidity sensor, execute the following on the MATLAB prompt:
To read the temperature from the pressure sensor, execute the following on the MATLAB prompt:
By default, the temperature is read from the humidity sensor. Hence, readTemperature(mysensehat) is same as readTemperature(mysensehat,'HumiditySensor').
Read the IMU sensor.
Sense HAT has an IMU sensor which consists of an accelerometer, a gyroscope and a magnetometer. The IMU sensor measures acceleration, angular velocity and magnetic field along the X, Y and Z axis. To read the acceleration, execute the following on the MATLAB prompt:
Supreme ruler 2020 mod. readAcceleration returns a 1-by-3 vector of acceleration values measured along the X, Y and Z axis.
To read the angular velocity, execute the following on the MATLAB prompt:
readAngularVelocity returns a 1-by-3 vector of angular velocity values measured along the X, Y, and Z axis.
To read the magnetic field, execute the following on the MATLAB prompt:
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Read the state of the joystick
Sense HAT has a 5 position mini joystick. Let us read the position of the joystick.
readJoystick returns the a value between 0 to 5 depending on the position of the joystick.
0 - Not pressed
1 - Centre
2 - Left
3 - Up
4 - Right
5 - Down
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The numerical values representing joystick positions are ordered with respect to the reference position of the Sense HAT. The HDMI port of the Raspberry Pi board facing downwards is the reference position.
You can monitor a particular joystick position by executing the following on the MATLAB prompt:
readJoystick(sensehatObj,position) will return a logical one if the joystick is in the specified position and zero otherwise.
Use the LED matrix
Sense HAT has a matrix of 8x8 RGB LEDs. You can set the color of a particular pixel, display an image or display a scrolling message on the LED matrix. Let us set the color of the pixel in the 3rd row, 6th column to cyan.
Observe that the pixel in the specified location is now cyan in color.
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The rows and columns are numbered 1 to 8. Pixel at location [1 1] is at the top left corner of the LED Matrix. The location is with respect to the reference position of the Sense HAT. The HDMI port of the Raspberry Pi board facing downwards is the reference position.
Color of a pixel can be specified by name. The supported colors are:
Red
Blue
Green
Cyan
Magenta
Yellow
White
You can also specify any other color by using a 1x3 array of R, G, B values. For example, setting the pixel to [255 192 203], would set it to pink. Now, let us display an image on the LED matrix.
The image must be an NxMx3 array of uint8 values. You can change the orientation of the displayed image by executing the following on the MATLAB prompt:
The Orientation of the image can be set to 0, 90, 180 or 270 degrees. These are defined with respect to the reference position of the Sense HAT. The HDMI port of the Raspberry Pi board facing downwards is the reference position.
LED Matrix can be used to display messages in the form of a scrolling text. The text scrolls from left to right. You can change the orientation of scroll by setting the 'Orientation' property of LEDMatrix. Let us display 'Hello World' on the LED Matrix.
By default, the text scrolls with a scrolling speed of 0.1 second and the color of the text is red. To increase the scrolling speed to 0.05 second, execute the following on the MATLAB prompt:
In order to set the text color to yellow, execute the following on the MATLAB prompt:
Similarly, in order to set the background color to white, execute the following on the MATLAB prompt:
You can rotate the text by specifying the orientation for the display. Let us specify orientation as 90 and display the text message.
Now, let us try to display a numeric value on the LED matrix. Read the value of temperature and display it on the LED matrix.
To clear the LED matrix, execute the following on the MATLAB prompt.
Summary
This example introduced the workflow for using MATLAB Support Package for Raspberry Pi Sense HAT.
Installation
In order to work correctly, the Sense HAT requires an up-to-date kernel, I2C to be enabled, and a few libraries to get started.
Ensure your APT package list is up-to-date:
Next, install the sense-hat package which will ensure the kernel is up-to-date, enable I2C, and install the necessary libraries and programs:
Finally, a reboot may be required if I2C was disabled or the kernel was not up-to-date prior to the install:
Hardware
The schematics can be found here.
Software overview
After installation, example code can be found under /usr/src/sense-hat/examples.
These can be copied to the user's home directory by running cp /usr/src/sense-hat/examples ~/ -a.
The C/C++ examples can be compiled by running make in the appropriate directory.
The RTIMULibDrive11 example comes pre-compiled to help ensure everything works as intended. It can be launched by running RTIMULibDrive11 and closed by pressing Ctrl+c.
Python sense-hat
sense-hat is the officially supported library for the Sense HAT; it provides access to all of the on-board sensors and the LED matrix.
Complete documentation can be found at pythonhosted.org/sense-hat.
RTIMULib
RTIMULib is a C++ and Python library that makes it easy to use 9-dof and 10-dof IMUs with embedded Linux systems. A pre-calibrated settings file is provided in /etc/RTIMULib.ini, which is also copied and used by sense-hat. The included examples look for RTIMULib.ini in the current working directory, so you may wish to copy the file there to get more accurate data.
Other
LED matrix
The LED matrix is an RGB565 framebuffer with the id 'RPi-Sense FB'. The appropriate device node can be written to as a standard file or mmap-ed. The included 'snake' example shows how to access the framebuffer.
Joystick
The joystick comes up as an input event device named 'Raspberry Pi Sense HAT Joystick', mapped to the arrow keys and Enter. It should be supported by any library which is capable of handling inputs, or directly through the evdev interface. Suitable libraries include SDL, pygame and python-evdev. The included 'snake' example shows how to access the joystick directly.
Calibration
Taken from this forum post.
Install the necessary software and run the calibration program as follows:
You will then see this menu:
Press lowercase m. The following message will then show; press any key to start.
After it starts, you will see something similar to this scrolling up the screen:
Focus on the two lines at the very bottom of the screen, as these are the most recently posted measurements from the program.Now you have to move the Astro Pi around in every possible way you can think of. It helps if you unplug all non-essential cables to avoid clutter.
Try and get a complete circle in each of the pitch, roll and yaw axes. Take care not to accidentally eject the SD card while doing this. Spend a few minutes moving the Astro Pi, and stop when you find that the numbers are not changing anymore.
Now press lowercase s then lowercase x to exit the program. If you run the ls command now, you'll see a new RTIMULib.ini file has been created.
In addition to those steps, you can also do the ellipsoid fit by performing the steps above, but pressing e instead of m.
Raspberry Pi Zero Wiki
When you're done, copy the resulting RTIMULib.ini to /etc/ and remove the local copy in ~/.config/sense_hat/:
You are now done.
Updating the AVR firmware
..
EEPROM data
These steps may not work on Raspberry Pi 2 Model B Rev 1.0 and Raspberry Pi 3 Model B boards. The firmware will take control of I2C0, causing the ID pins to be configured as inputs.
Enable I2C0 and I2C1 by adding the following line to
/boot/config.txt:Enter the following command to reboot:
Download and build the flash tool:
Reading
EEPROM data can be read with the following command:
Writing
Raspberry Pi
Please note that this operation is potentially dangerous, and is not needed for the everyday user. The steps below are provided for debugging purposes only. If an error occurs, the HAT may no longer be automatically detected.
Raspberry Pi Hat List
Download EEPROM settings and build the
.eepbinary:Disable write protection:
Write the EEPROM data:
Re-enable write protection:
