An “Advent wreath” is a horizontal wreath, traditionally with four candles which are lit successively to mark each of the four weeks of Advent in the liturgical calendar of some western-tradition Christian churches. Alexander Weber has produced an elegant little electronic version that uses 4 LEDs, a coin cell, a coin cell holder, a paperclip, and an 8-bit microcontroller chip. It is light-responsive, and uses one of the LEDs in “reverse” mode as a photodiode to detect darkness. The LEDs flicker, and the number of LEDs lit at any point is cycled by briefly cutting the power. Awesome design.
Beautifully minimal LED Advent wreath circuit and device