In fact, I2C is the backbone for a lot of side channels like these – it’s also one of our preferred interfaces for connecting to cool sensors, and in this case, an OLED display!

Learn how to create a simple heart rate monitor using an Arduino Pro Mini, PulseSensor, and OLED display. This ...

"It's a bare OLED display with a 30-pin FPC (I2C), which I got from my trusted display supplier." Each key's display can change depending on context.