Knowing that I want to work with the buttons from the calculator i decided to attach wires to the button connections and power supply. I removed the internal battery and changed it for the arduino power supply. The voltage could also be adjusted for different effects.
After a quick test it was clear that the received signal was more complex and detailed than I would have guessed. The challenge now is to convert the information into something meaningful.
I will experiment with audio, visual outputs, and concepts for subverting the preconception of what a calculator is. Resulting in a confusing user experience which will lead to playful exploration of a "new" device.