Joule Thief Steals in Favor of Christmas

A lot of things tend to get stretched during the holiday season, like shopping budgets and waistbands and patience. This year, [Chris] is stretching the limits of both the mini breadboard and the humble 1.5 V LR44 coin cell with his joule thief-driven LED mini Christmas tree.

With the push of a micro momentary, the joule thief circuit squeezes enough power from an LR44 to boot an MSP430 microcontroller, which needs 1.8 V – 3.6 V. After boot, the micro takes control of the joule thief circuit and milks it whenever the voltage falls below 3.2 V. This tree may be small in stature, but it’s feature-rich. A push of the same momentary button cycles through four different light shows, ending with a medley of all four. Be dazzled after the break.

The code for this tiny tree, which features an awesome ASCII breadboard layout and schematic, is up on GitHub. [Chris] has it listed among a few other manageable bare-metal ‘430 projects that would be great for beginners at pure C. If that sounds like you, why not give yourself the gift of learning a new language?

We’ve seen some spirited ways of lighting LEDs, but doing it with candle power takes the fruitcake.

14 thoughts on “Joule Thief Steals in Favor of Christmas

  1. I wonder what the absolute lowest cell voltage this would work down?
    I’d guess if a 3-stage discharge SMPS to utilize efficiencies of each to both maximize runtime and to maximize the full-to-discharge (Brownout) voltage difference.

    The 3x stages can be:
    1st a standard boost configuration using MOSFETs in a “diode emulation” mode during boost (i.e. 2x MOSFETs one in blocking or off whilst the other is conducting) for highest cell voltage stage efficiency,
    When the cell voltage drops below a defined amount, then an initial voltage stored in a capacitor starts the BJT-joule-thief stage that is then linked via a change-over circuit (a simple MOSFET),
    And the last stage is to have a MOSFET/JFET combo driven Joule thief circuit started up before switching over to that for the cell to reach to near 0V as physics can possibly allow.

    This method of bootstrapping an SMPS in a chain according to the current cell voltage as determined by the most efficient voltage ranges for each SMPS variant can produce a total of the average of the nearest to the maximum efficiency of each stage (Presumably the RMS of the efficiencies, i.e. 90%, 72%, 83% being overall 82% efficient over the lifetime of the battery)
    .
    .

    BTW is there a rule where we cannot just get an oldskool round buiscuit tin, some opened up cells and build our own coin-cells by strapping parts of the opened cells togehter to make a completely custom rechargeable super coin cell?

    I’m thinking I’ve got about 15KAh worth of cells I could source, splice their sheets together and cram into a safely lined tin… and plenty of sealant to insulate the lid from the walls ;D
    Or do we then have to make a coin-cell holder for this custom size

    1. The problems with making “rules” for a Hackaday contest:
      a) Too many hamper creativity
      b) People will circumvent them anyway
      c) They don’t reflect the spirit of our judging — if it’s cool, it’s cool. If you can pack a fusion reactor into the shell of a CR2032, I’m pretty sure we’ll make an exception to whichever rules that might have violated. Well, except the laws of physics. Those, we abide by.

      1. Hmmmm, though the face of my manager already goes several shades of blue every time when he sees I’m charging manufacturer condition cells with a bench PSU,
        then to have my manager catch me unseal them (The pouch ones) and roll the contents into the destination “cell bath”… especially if the layers were to spontaneously combust due to air or short… or the whole destination cell were to blow:
        I’m likely without a job and a manager requiring both a CPR and ritualistic resurrection.

        If I can find a safe place to make this… then I’ll enter, even if just to split the readers into those whom LOL over such a thing and the others whom scream into the comments on how lucky the world hasn’t just blown up.

        BTW, the cell I’m thinking about building would be a 10x scale model ;)
        maybe a “The most creative and awesome cheat/rule-bending” entry as a future idea on these sort of contests.

        1. You are only elibible for the prizes if you’re still alive on Jan. 8th. :) Seriously, be careful where care is needed.

          Re: 10x scale model. Some folks have already hinted about using CR2477s, which are seriously big cells. Of course, we’d expect those projects to be proportionally more impressive. (You’re not going to fool us just by using more power.) But building your own cell has to count for something, just on its own, right?

          If you have a 50mm LED to go with it… 10x throwie. (Oh no!)

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