Singing hula-hoop. My first experience programming an Arduino microcontroller and demoing it to the public at the school Christmas party. I modified a few pieces of code to first use a range sensor to take in distance values, and a piezo buzzer to sound different tones according to those values. I can’t say I planned on attaching it to the hula-hoop from the get-go, but liked it once I gave it a try. A very noisy toy - the tones scale up and down as the hoop goes round.