A theremin is an electronic musical instrument that you can play without even touching it - spooky! The theremin senses the distance from its antennae to the player's hands, and changes its pitch and volume based on these distances. The theremin was used to make soundtrack music for many iconic spooky movies, like The Day the Earth Stood Still (1958), and is perfect inspiration for a Halloween project!
Here, I've turned a pumpkin into a Jack-o-Theremin using an ultrasonic distance sensor and a Circuit Playground Express (CPX). The CPX uses the distance measurement to generate a sound and flash the onboard NeoPixels in various colors. This version of a theremin has a much more digital-bleepy-bloopy sound than a traditional theremin, but you still get to make music by waving your hand around in the air!
Note: For my project, I used a scavenged speaker that I had in my spare parts box, but the speaker listed above will work just fine!
You'll also need a pumpkin to carve, and I highly recommend choosing a plastic or foam pumpkin for this project. That way, you can enjoy your Jack-o-Theremin for many Halloweens to come! If you do build this into a real pumpkin, you'll need to cover all the electronics with plastic wrap or seal them in a plastic bag inside the pumpkin.