This is a generic embedded driver for the Sensirion SCD4x Carbon Dioxide Sensor. It enables developers to communicate with the SCD4x sensor on different hardware platforms by only adapting the I2C communication related source files.
So we need to adjust two files according to your platform.
This file contains the implementation of the sensor communication
(how to send requests to the sensor). Therefore, how this is done depends on your
hardware platform. Therefore we can only provide function stubs in which you
can implement the logic yourself.
There are sample implementations available for some platforms: sample-implementations.
If you are using a Linux based platform like Raspberry Pi
you can just replace the unimplemented HAL template with the provided
implementation in sample-implementations/linux_user_space/:
cp sample-implementations/linux_user_space/sensirion_i2c_hal.c ./
If you are on a Linux based platform you can skip this part since everything is already correctly setup for you.
Otherwise you need to check if the libraries <stdint.h> and
<stdlib.h> are provided by your toolchain, compiler or system.
If you have no idea on how to do that you can skip this
step for now and come back when you get errors related to these names when
compiling the driver.
The features we use out of those libraries are standard integer sizes
from <stdint.h> and NULL from <stdlib.h>. If they are not available
you need to specify the following integer types yourself:
int64_t= signed 64bit integeruint64_t= unsigned 64bit integerint32_t= signed 32bit integeruint32_t= unsigned 32bit integerint16_t= signed 16bit integeruint16_t= unsigned 16bit integerint8_t= signed 8bit integeruint8_t= unsigned 8bit integer
In addition to that you will need to specify NULL.
For both we have a detailed template where you just need to fill in
your system specific values.
Now we are ready to compile and run the example usage for your sensor.
Take the .c and .h files directly in this folder pass them to your
favorite C compiler and run the resulting binary.
This step may vary, depending on your platform. Here we demonstrate the
procedure for Linux based platforms:
- Open up a terminal.
- Navigate to the directory where this README is located.
- Run
make(this compiles all the code here to one binary). - Run
./scd4x_i2c_example_usage(This will run your newly compiled binary). - Now you should see the first measurement values appear in your terminal. As a next step you can adjust the example usage file or write your own main function to use the sensor.
In these files you can find the implementation of the I2C protocol used by Sensirion sensors. The functions in these files are used by the embedded driver to build the correct frame out of data to be sent to the sensor or receive a frame of data from the sensor and convert it back to data readable by your machine. The functions in here calculate and check CRCs, reorder bytes for different byte orders and build the correct formatted frame for your sensor.
In these files you can find the implementation of the hardware abstraction layer used
by Sensirion's I2C embedded drivers. This part of the code is specific to the underlying
hardware platform. This is an unimplemented template for the user to implement.
In the sample-implementations/ folder we provide implementations for the most common
platforms.
In this file we keep all the included libraries for our drivers and global defines.
Next to sensirion_i2c_hal.c it's the only file you should need to edit to get your
driver working.
In these files you can find some helper functions used by Sensirion's embedded drivers. It mostly contains byte order conversions for different variable types. These functions are also used by the UART embedded drivers therefore they are kept in their own file.
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