micro:bit Christmas Wreath Lights

Last updated on Jan 26, 2023

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)

Progress

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
            basic.pause(100)
            basic.showNumber(hour)
            basic.pause(100)
            // Only show UI how-to guide once (otherwise would be called on every increment/decrement)
            if (helpShownCount < 1) {
                upOrDownHelp()
                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!
    basic.clearScreen()
    basic.showIcon(IconNames.SmallHeart)
    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 $0 \leq t \leq 23$.