I was having a Raspberry Pi Zero sitting on my desk for a long time, searching for something to do with it. I also wanted to to learn STM32, mainly DMA and interrupts. As the calculator is powered by an STM32F412, why not put them together ? TL;DR, the result: The idea was to add an application on the calculator, which will display the output of the Raspberry Pi, and send keystroke from the keyboard to it.