(Signature) | Video released under CC BY 4.0.

The nice thing about Christmas holidays is that you actually have the time to make shower thoughts a reality.


  • 1 × Arduino Uno. It will also work on other Arduinos (subject to pin number changes), and should also work on other boards, as long as there are 3 digital GPIO pins that can sink ~30mA, 1 PWM output pin, and a 5V rail.
  • 3 × red LEDs, 3 × yellow LEDs and 3 × green LEDs. I’m using whatever comes with the Arduino kit. It should work if it drops ~2V drawing ~10mA each. The code can be easily adapted if you want to add more colours, as long as you have three LEDs for each colour.
  • 3 × 100Ω resistors. I don’t have them so I’m using two 220Ω resistors in parallel to replace each 100Ω.
  • 1 × passive buzzer or speaker. I’m using a KC-1206 which came with the Arduino kit, but I’ve also tested an AST-030C0MR-R (which came with the Chaotic Oscillator kit) and a 4Ω 3” speaker (part number starts with EAS8 but the rest is illegibe due to rust) which I scavenged from an FM radio receiver.
  • A breadboard and a bunch of breadboard wires.
  • A power supply. I’m using USB.



gEDA schematics: xmas.sch (Signature), arduinoUNO.sym (Signature), speaker.sym (Signature).


A score for the song was looked up and its melody was written out as an array of the standard pitches in int song[]. int durations[] has the same length as song and denotes the relative length of each note. int durationScaleFactor controls the tempo of the song.

Arduino code: xmas.ino (Signature), pitches.h (Signature).