A Joule thief: (1) is a device that will suck and all of the juice from your "dead" batteries (2) To make it possible for an LED with a voltage requirement of higher than 1.5 volts to run off of a single 1.5 volt battery! For example, run a white LED from a single AA battery! or im my case run 2, 4volt Leds off a battery measuring 1.2 volts on a voltmeter!!!!
I made using 1ups instructable. I just added a switch and put the project in an old Chocolate tin (Altoids tin).
if your wondering what the coil is/ what it dose. Its a hand wound Toroid. I got 15 Toroid Beads out of my old dead x box.
HOW IT WORKS
This circuit works by switching current back and forth 40hrtz (40,000 time per second) the Coil builds up a charge from the >1.5volt battery once it build to 4-8 volts it switches the power to the Leds, they light up and then the current is switched back to the Coil and the Cycle repeats faster than you eye can see.
great use: writing with light
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