Make:

Great project, make sure you have a look at the rusty nail version of this also. :)
http://hackedgadgets.com/2007/03/22/rusty-nail-led-night-light/

Get everything you need (except the toroid) for $0.83
http://hackedgadgets.com/2007/11/02/make-a-joule-thief/

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Here's an idea. Joule Thief, blinking, LED throwies? How long could we string out their lifetime?

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The whole idea of a joule thief is to step up a low voltage to a voltage suitable for the LED. The button cells used in throwies are capable of powering the LED without any stepping up... and it would just complicate things.

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When your throwie battery drops below the LED threshold voltage it will stop working. The step up feature is nice because it will run on a nearly dead battery even if it is below the LED threshold voltage. The stepup won't burn out the LED with a fresh battery because the duty cycle is very low.

There is some critical info missing from this design, however. How many turns of wire go on the toroid, and
which type of toroid core is used (they are
color coded)?

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What's the point of an article like this without explaining how it works? Or even linking to an article that explains how it works?

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bigben: such is the way of the maker, heavy on photographs, light on theory. ;-P.

I just built one of these and posted a brief explanation and some oscilloscope photos on my website:

http://jormungand.net/projects/joule/

enjoy.

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I has posted a .asc file that you can DL and run in SwitcherCAD to simulate operation of the circuit. It's a very small circuit so the file is very small (http://www.rehorst.com/mrehorst/Low_V_LED_driver.asc

Have fun!

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The idea of the circuit is really neat and I believe that everyone could use some extra information. As previously stated, Hack-A-Day linked to one of these that, with it's LED, fits into a small incandescent bulb.

I hate when people link to the blog instead of the article, but there is a good discussion on the Hack-A-Day posting:
http://www.hackaday.com/2007/10/10/joule-thief-led-driver/

The original article:
http://www.emanator.demon.co.uk/bigclive/joule.htm

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Joule Thief type circuits are beginning to be common in some simple appliances -- look for a single-AAA-cell Ray O Vac "Brilliant Solutions" penlight for $2.99 and there'll be one inside. Probably a lot of other places to harvest them from as well...

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