Yet another Raspberry Pi + Sense HAT C/C++ library

Foreword

This repository aims to resume the Python Sense HAT API in the C/C++ programming language. The functions provided by this library are intended for students who are taking their first steps in programming. Therefore, we use a very small subset of the C++ programming language.

• No classes. Okaaaayyy! I know. Don't slap me, even virtually.
• Typed input/output through iostream. Almost avoids burdens of C stdio formatting.
• Use of IMU RTIMULib library already written in C++. Much more convenient to get magnetic field measures from LSM9DS1 registers.
• Use of libgpiod for GPIO functions.
• Use of sysfs for PWM0 and PWM1 output channels.

The code in this repository has been compiled from various other repositories. It then developed into a full library with the addition of GPIO and PWM functions.

• libsense
• Raspberry Pi Sense-HAT add-on board
• Sense Hat Unchained

Install and build

Open a terminal on your Raspberry Pi.

1. Your Raspberry Pi user account must belong to a few system groups to access hardware devices and install the library file once it is compiled.

The result of the id command below shows the user account belongs to the required system groups.

id | grep -Eo '(input|i2c|gpio|spi|sudo|video)'

sudo
input
gpio
i2c
spi
video

Check that the sense-hat packages are already there.

apt search sense-hat | grep install

python3-sense-hat/stable,stable,now 2.6.0-1 all  [installé, automatique]
sense-hat/stable,stable,now 1.4 all  [installé]

2. Install development library packages

sudo apt install libi2c-dev libpng-dev libgpiod-dev

3. Clone this repository

git clone https://github.com/platu/libsensehat-cpp.git

4. Build the library and compile the example programs

cd libsensehat-cpp/ && make

Depending on the number of example programs, the compilation may take some time.

You're all done ! Now you can open the example files and run your own tests. There is a generic Makefile in the examples directory which you can copy and modify to suit your needs.

Start new project

To start a new project, you need to copy the Makefile file to your working directory.

mkdir myProject && cd myProject
cp $HOME/libsensehat-cpp/labTemplate/Makefile .

Then, you can copy the example program that is closest to your needs and adapt it to your project.

cp $HOME/libsensehat-cpp/examples/01_setRGB565pixel.cpp .

Run make to compile the program.

make

g++ -Wall -Wextra -Wduplicated-cond -Wduplicated-branches -Wsign-conversion -Wlogical-op -Wuseless-cast -Werror -pedantic -std=gnu++2a -o 01_setRGB565pixel 01_setRGB565pixel.cpp -lsensehat-c++ -lpng -li2c -lm -lRTIMULib -lgpiod

Run the program.

./01_setRGB565pixel

Settings file not found. Using defaults and creating settings file
Detected LSM9DS1 at standard/standard address
Using fusion algorithm RTQF
Detected LPS25H at standard address
Sense Hat LED matrix points to device /dev/fb0
8x8, 16bpp
IMU is opening
min/max compass calibration not in use
Ellipsoid compass calibration not in use
Accel calibration not in use
LSM9DS1 init complete
Joystick points to device event4
-------------------------------
Sense Hat initialization Ok.
  [ f800 ]   [ fc00 ]   [ ffe0 ]   [ 7e0 ]   [ 7ff ]   [ 1f ]   [ f81f ]   [ fc10 ]
Waiting for keypress.
-------------------------------
Sense Hat shut down.

In addition to this manual method, students run the getLab.sh script to create a new project directory. The script creates a new project directory in the $HOME/cpp location and copies the Makefile and VScode settings files into it. Here is an example of how to use the script.

$HOME/libsensehat-cpp/getLab.sh myProject

When using Visual Studio Code, the two compulsory extensions are:

• C++ Extension Pack
• Makefile Tools

Example programs

Almost every function has its own example program that illustrates how it works. Source file numbering in the directory named examples designates the category of functions. Here is a list of these categories:

• 01 Get or set a single pixel
• 02 Get or set all pixels
• 03 Flip or rotate all pixels
• 04 Display a character or scroll a message
• 05 HTS221 Humidity sensor and LPS25H Pressure sensor
• 06 LSM9DS1 IMU Orientation and compass
• 07 Joystick events
• 08 GPIO read input or write output on Raspberry Pi pins subset
• 09 2 PWM channels
• 10 Color detection based on TCS34725 (work in progress ...)
• 11 Console keyboard events routines

Library addons

Once the Sense HAT standard header is replaced by a stacking header, GPIO and PWM pins are available.