RP2040 Quadrature Encoder

Encoder

An interrupt based quadrature encoder for the RP2040.

This simple OOP approach to an encoder is enabled by static variables and templates: The interrupt service routines (isrs) are called without a reference to their object. The static keyword is used to still allow access to object variables. Static variables are the same for all instances of a class. So we trick the compiler into creating a new class for each encoder using a template.

Instanciation may look somthing like this, note that Quadrature_encoder<MY_DATA_PIN, MY_CLK_PIN> is the name of the class:

Quadrature_encoder<DATA_PIN, CLK_PIN> my_encoder = Quadrature_encoder<DATA_PIN, CLK_PIN>();

After construction call begin() during setup and count() to get the steps since the beginning.
end() usually must not be called.

GPIO Interrupt Handler

Because the RP2040 can only have one gpio_isr the gpio_irq_handler is used to allow one function call to be registered per pin.

This header creates an interface using a jump table, allowing the user to attach pin and core specific callback functions.

You may

#define DEBUG_IRQ_DURATION_PIN 11 //for example
To debug the duration of your ISR with a logic analyser. This will switch the pin high during the ISR and low otherwise.

and

#define HIGHEST_INTERRUPT_PIN 15 //for example
To safe some memory in the jump table, but disabling interrupts on pins higher than specified.

CMake, Include, Build

1. Clone this repo e.g. to myproject/include/RP2040-Encoder
2. Add the repo the .gitmodules file as a submodule, adding:

[submodule "Encoder"]
path = include/RP2040-Encoder
url = https://github.com/tobiglaser/RP2040-Encoder.git
branch = main

3. Tell CMake where to find the new include files, adding this somewhere after add_executable() in CMakeLists.txt:

# Add Encoder
target_include_directories(my_project PUBLIC include/RP2040-Encoder)

4. Copy an example to your main.cpp and try it out.
   Refer to Pico-FreeRTOS-Project-Template for a FreeRTOS template.

Attribution

The approach using templates and static variables was inspired by zacsketches/Encoder.