The four LEDs are hidden inside the sea glass and kept inside an old glass jar.
The code is pretty simple. It uses the Adafruit NeoPixel library to drive the four LEDs. The LEDs are literally cut with scissors from a strip and then bent into a circle and super-glued together.
The breathing is based on the old “sleep LED” on Macs (the explanation I originally used was to be found here and can now be found on the Internet archive). (Note that Adafruit’s Ladyada did some reverse engineering work on the Mac’s breathing light way back and the origin of the formula is from a comment on her post).
The formula for the LED brightness is
where x is the number of milliseconds since start. It looks like this when plotted (there’s a sharper intake of breath than exhalation):
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