Rusty OBEGRÄNSAD

Display custom animations on IKEA's OBEGRÄNSAD using Rust on the Raspberry Pi Pico.

Interfacing with OBEGRÄNSAD

OBEGRÄNSAD consists of 16 daisy-chained SCT2024 16 bit serial-in/parallel-out constant-current LED drivers. After de-soldering the on-board microcontroller, the Raspberry Pi Pico can be connected to the Clock, Data In, Latch, and inverted Enable inputs of the SCT2024 chain. These inputs as well as +5V and GND can readily be accessed at the bottom of the OBEGRÄNSAD PCB that contained the original microcontroller. In order to interface with the 5V CMOS inputs of the SCT2024, a level shifter is required to translate the 3.3V outputs of the Pico to 5V. I assembled a helper board for level shifting using an SN74AHCT125, wired up as shown in the following schematic:

The timings for the SCT2024 are such that the Clock and Data In lines can be driven by SPI. To latch the transmitted data to the LEDs, a short positive pulse on the Latch line is required.

Note that the 16 LEDs driven by one SCT2024 are laid out in a circular pattern around each chip such that it is non-trivial to index the LEDs of the display. While one can derive an algorithm to compute the index of an LED, I found the algorithm to be not very readable and only used it to compute a look-up table to index the LEDs/pixels.

Implementing custom animations

A custom animation for the display should implement the animation::Animation trait with its only method render_frame. The return value of the render_frame method indicates for how long this frame should be displayed. When implementing this method, you typically want to use display.clear() to erase the current contents of the display and then draw your frame using display.set_pixel(x, y).

To show your custom animation on the display, add a mutable reference to an instance of the animation to the animations array in main.rs. The button of the display can be used to cycle through the different animations.

Generating a UF2 binary

Ensure that Rust is up-to-date, target support for thumbv6m-none-eabi is provided, and elf2uf2-rs is installed:

rustup self update
rustup update stable
rustup target add thumbv6m-none-eabi
cargo install elf2uf2-rs

Execute cargo run --release to generate the UF2 binary at target/thumbv6m-none-eabi/release/rusty-obegraensad.uf2.

git setup

GitHub noreply email

git config user.name "a-johanson"
git config user.email "a-johanson@users.noreply.github.com"

GitHub tokens

git remote add origin https://a-johanson:<TOKEN>@github.com/a-johanson/rusty-obegraensad.git
git push -u origin master