Arduino Power Moon

It's that time of year again so time for a Christmassy sort of project to round out the year. In the past I've 3D printed lots of Christmas decorations, so I thought it was time to make a nice Christmas tree topper. Normally this would be a star, but my son has been playing lots of Super Mario Odyssey lately, and I wanted to make something he would think was cool, so I went with a Mario-style Power Moon from the game.

I wanted to add a bit of light and sound, so I started digging through spare Arduino boards to see what I could make work with battery power in a minimal footprint. I ended up using a Adafruit Gemma m0, as it's small, has a battery JST input, on/off switch and a single Dotstar three-colour LED mounted on the board already. All I needed to fit in with it was a small lipo battery and 8ohm speaker for sound and it was good to go.

I wanted the power moon to be able to change colours (as they appear in various colours in the game, depending on which kingdom you are in), so I 3D printed the moon using transparent filament and designed a little cavity inside the moon to house the electronics and light. The resulting effect with the LED on is that the filament catches the light and creates a nice glowing effect.

For music, I wanted to go just a little step beyond a series of single tone beeps, so I did a little research on how to get timer counters and interrupts going on the Gemma m0 (and other SAMD boards), mainly by studying the existing Arduino "tone" implementation for this chip. I ended up creating a modified set of tone functions that use both timer 4 and 5 to generate two pulse wave voices so I could play some very basic polyphonic music. There are three I/O pins on the Gemma and I wanted to keep one free as a switch to control the activation of lights and sound, hence just two sound channels.

For the electronics, I soldered the Gemma pins directly to each end of the speaker (via a pair of resistors) and wired up a vibration-activated switch between one of the digital inputs and ground, so that I could trigger light/sounds shows without having to put in a button, or open up the case. I fit a small lipo battery in between the Gemma and the speaker, so everything is together in a small disc-shaped package.

For music, I composed some two part tunes using Musescore and wrote a little python script to convert Musescore mscx files (XML formatted files that contain the music data in terms of the note pitches, timing and durations) into data embedded into a header file I could compile straight into the Arduino code. I then wrote a system in for pulling out the appropriate note data at the appropriate time to pass on to the modified tone code.

The moon is made up of two halves that need to be able to come apart (in order to switch it on/off and take the battery out for re-charging), so in order to have something that can open and close easy, I glued some small magnets to the inside of each side of the case that hold the moon together. Seems to work pretty well!

Here's a video of the moon in action: Merry Christmas!




Design Files:

3D Printed Case STL files:
https://www.thingiverse.com/thing:4047914

Code for running the power moon:
https://github.com/mit-mit-randomprojectlab/power_moon