Subscribe to Make Magazine Today!

1827215708 08C672Ecbf

You’re going to need a white or blue LED that is rated for 3 volts, a 1K resistor, a 2N 3904 NPN transistor, a toroid, two pieces of wire and a battery.

1828270262 B76C867954

You might even be able to scavenge this stuff out of your junk pile of electronics… you have a junk pile of electronics right? PDF Link

You can get the video and this pdf in itunes automatically! – iTunes Subscribe Link

Update: Windell posted more info and a detailed walk through of the toroid winding process. – Link


  • abbtech

    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/

  • jbond

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

  • n3rrd

    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.

  • rehorstmark@netscape.net

    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)?

  • bigben

    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?

  • eckern

    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.

  • rehorstmark@netscape.net

    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!

  • n3rrd

    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

  • MadScott

    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…

  • joedupont

    they mention blue and clear LED’s I have yellow .. why won’t my yellow led’s work? I’ve tried all kinds of windings , two sizes of torides, etc. etc. I can’t get these to run
    Is this a hoax? I don’t think so but I can’t seem to make this happen. it would seem to me that making low voltage usable is something worth developing. Even tree power might have some applications..

  • joedupont

    what about other colors of LEDS?
    Why don’t they mention them?
    Will it work on yellow, green or red???

  • sohaib Asif

    I have make a joule thief but its not working What should I do????????????

  • http://gbleezy.com Graham Savai’i Hart

    Cool cool!

Related Supplies at Maker Shed