This Miniature Joule Thief, Built From Upcycled Parts in a Fuse Case, Is a Really Bright Idea
Drawing its power from a 10-year-old watch battery, this double-LED circuit is a miniature marvel.
Pseudonymous maker "w" has built a Joule thief circuit with a difference: this miniature glowing marvel is installed entirely inside the glass housing of an old fuze, bar the battery from which it slurps power.
"Miniature 'Joule thief' in a fuse case," w writes of the project, "powered by a 10 year old watch battery."
The build is a masterclass in upcycling: not only is the case from an old fuse and the battery from a long-dead watch, but the inductor inside is salvaged from an Ethernet transformer. The glow, meanwhile, comes from a pair of 0805-footprint surface-mount LEDs installed back-to-back.
Joule thieves, the concept for which dates back to a patent for oscillator circuits filed in 1930, are designed to pull the last drops of power from seemingly-dead batteries. Taking the form of a blocking oscillator configured as an unregulated voltage boost converter, they're popular builds for low-cost torches capable of running when off-the-shelf devices would refuse to start.
More information is available in w's Twitter post.