micro:bit Christmas Wreath Lights

Implementing a low-power solution to turn a set of LED Christmas lights on and off during a user-specified timeframe.

Table of Contents

Design choices

  • Used micro:bit as the other option was a Raspberry Pi 2, which would have consumed more battery and would have been too heavy for the wreath
  • Used blocks in the MakeCode editor 1, for accessibility
  • Track 3 things: current time, on/start time and off/end time
    • Only use hours for start/end time, to keep the user interface simple
  • Allow manual override (mostly for testing)
  • The initial idea was to provide this over a simple server and web GUI, but I didn’t have a Wi-Fi card for the micro:bit
    • Use the micro:bit LED display
    • Minimal text to avoid scrolling (prefer icons)


Turning things on and off (On the breadboard)

  • Built the basic on/off functionality first using one LED, using Pin 16 and the GND
  • A for ON, B for OFF - this later became the manual override
  • Clicking each button rendered a happy/sad face on the micro:bit display to provide user feedback

Automating according to time

  • Used the micro:bit time library 2 to track the time
  • Two variables track an “ON” time and “OFF” time (hour only)
  • Every minute, depending on the current time, the lights are switched/stay on or off

Configuration UI

This was the longest part to write

// Used to constrain input hour input
// This could be simplified as "Math.abs(hour) % 24"
function normaliseHour (hour: number) {
    if (hour > 23) {
        return 0
    } else if (hour < 0) {
        return 23
    return hour

function changeHour (hour: number, name: string) {
    // Minimal text used - the less scrolling, the better
    basic.showString("SET " + name + "?")
    if (yesOrNo()) { // Custom UI element, returns true (yes) or false (no)
        helpShownCount = 0
        while (!(input.buttonIsPressed(Button.AB))) {
            // Pausing so that A+B input can be detected, which will move to next setting
            // Only show UI how-to guide once (otherwise would be called on every increment/decrement)
            if (helpShownCount < 1) {
                helpShownCount += 1
            if (upOrDown()) { // Custom UI element, returns true (up) or false (down)
                hour += 1
            } else {
                hour += -1
            hour = normaliseHour(hour)
    // End with a heart icon!
    return hour

Testing & Tweaking

  • Considered an approach where micro:bit used to relay AA battery supply, used normal AAA battery for micro:bit + lights… for now
  • Pin 16 determined to be rubbish, used Pin 2 as more easily reachable - cross checked with the micro:bit website 3
  • Duct tape used to tape wires through the crocodile clip loops
  • Flashed some final tweaks to print 24 hour current time correctly and some defensive coding to ensure hour value input is $0 \leq t \leq 23$.

The Wreath
The Wreath… can you spot a micro:bit ;)

Final Blocks Code
Picture of the final code in blocks, the blue blocks in the bottom left are UI functions

Next Steps and Future Work

  • Could refactor hour normalisation to use modulo 24
  • Allow setting of minutes for the current time
  • Improve UI to shorten text and make navigation faster
  • Buy some card and make a battery pack holder 4
  • Install Wi-Fi card and implement localhost web-based interface
Timothy Clark
Timothy Clark
Software Engineer

Software Engineer with interests in cyber security and computing education.