Joule Thief

[SeaMonkey]

There are a number of low voltage (single cell)
LED Driver Chips available such as the ZETEX
ZXSC300 which have surprising capabilities.

Discussion here.

Datasheet here.

It does require an external transistor so
one of the other chips with integrated
switching transistor may be more convenient
to some experimenters.

Search "single cell led driver."

[Pirate88179]

Bill:

I agree that the project will be a challenge.  Perhaps you could get others involved.  It's definitely doable with the people around here.  I honestly don't think I will have the time to follow and contribute that much.  Consider me the "hardware architect" and take it from there.  That's supposed to be part of the fun also, to develop it as a group effort and create the schematic and define the timings and select the parts yourselves.

You might actually need more than 4.5 volts to power the 555 because it has to generate sufficient gate voltage for the MOSFET you end up using.  The answer is in the spec sheet for the MOSFET.  Of course the batteries will still last years.

Then of course you have complete freedom to choose your inductor and also to define the timing, as was discussed a few postings ago.

In the second revision you may be able to experiment with over-driving the LED for a very bright flash of light.  The spec sheet may state something about an extra bright flashing mode and recommend the current level and the pulse length.  I haven't read a modern power LED spec sheet so I am just speculating.  This would be for a "beacon" function, just for fun.

MileHigh

MH:

Well, I was hoping for at least a crude schematic.  I would be lost without one.  I know there are others here that will do this and, hopefully, they will jump on board.  You see, I thought I was following your idea but, I am not sure why we need an external transistor, mosfet?  There are many on that 555, are they not isolated for our use?  (showing my ignorance here)  Is there a low voltage 555 that is separated that we could use?  I was hoping to see where the 555 pinouts and the mosfet leads would be connected.  I have no idea how to do this.  I suppose I am smart enough to learn, which is, afterall, part of the fun but, it may be beyond me.

I still love your idea though, and maybe this will force me to learn all about 555's and mosfets.  It will be a while before I can buy some of those in your pdf.  Money is tight this month so I have some time to study.  I still think this could be a breakthrough in the JT experiments we have seen here.  I am still dedicated to giving it my best efforts.

Bill

@Seamonkey:

Thanks for the links.  It was funny that today, an electronics guy where I work told me to go to the same forum.  Interesting.

Thanks,

Bill

[MileHigh]

Bill:

You need an external transistor or MOSFET to do the power switching to drive the LEDs.  The 555 can't do that, it's just a timing device.  All that you need is the cheapest CMOS 555 so they should be cheap.  You don't need a fancy low-voltage 555.

I can't remember if you have a scope, but ideally you would have one for this project.  You can simply Google 555 circuits and pick one.  But I realize doing the whole thing is outside of your comfort zone.

It would be a nice simple (relatively) Arduino project also, and for sure there has to be software already written that you could hijack for this project.  There are also ways to make some micros, probably including models in the Arduino family, to run at ultra low power.  So the whole timing setup could be done by a micro and probably run at about the same nearly insignificant power level.

Sorry I can't be directly involved if it were to happen but it's not the time for me and it's also a big commitment.

MileHigh

[MileHigh]

Bill:

Necessity is the mother of invention so I dreamed up a great consolation prize for your consideration.

I can suggest a simplified version of the project that you could do and it gives you a bootstrap or launching pad for doing the real project.  Just get an Arduino board, I think they are about 20 bucks?  Find the software.  Search on something like, "Arduino software oscillator" or "Arduino PWM oscillator" or "Making the Arduino programmable I/O into a square wave generator."  (There might be hundreds of them out there.)  The Arduino board will have a few input-output bits for driving external logic.  So the software will make one of those I/O bits in to an output bit and turn it into a square wave output where you can control the frequency and duty cycle.

So you connect that output signal to the base resistor of your transistor.  The external battery ground is connected to the ground pin for the digital output.  Then you just do the usual circuit:   battery -> coil -> transistor collector.  And coil -> LED -> ground.

Then you are ready to roll.  You can use all of your existing coils and transistors.  But you have the freedom to try any of your coils or any battery voltage, and the Arduino program allows you to dial up any frequency and any duty cycle for the energizing of the coil.  It's basically a quick and easy test bed setup.

Note of course the "test bed" is a very short step away from an actual usable project.  You just flash the Arduino board with the program and give it it's own button cell or cells.  Then connect up the "power train" and you are done.  Some of those Arduino boards are the size of a USB key.  So the USB key and the two button cells could be tucked away inside a project box and you add the power train with the replaceable AA cell, the coil, the transistor and LEDs and you are done.

MileHigh

[MileHigh]

Bill:

I can't resist finishing off the software for the simple design.  The Arduino board will have those programmable input-output bits.   Some of them are used as inputs, and they are used for reading the momentary push buttons you see on some Arduino boards.  Also, almost certainly you can program one of those pins to make the Arduino go to sleep.  Then the next time you push it the Arduino wakes up.  When the board is "asleep" it consumes almost no power.  So you don't even need a physical on-off switch, the batteries are always powering the board but the board consumes no power when it is asleep.

So you can imagine this:  Your JT-style LED light sitting on top of some sort of project box.  Perhaps the holder for the single AA battery is conveniently accessible and open and flush with the top surface of the box.   And on the front of the box there is a little tiny panel-mount momentary push-button switch.  It cycles though off -> low -> medium -> high -> off.  All very simple and elegant.

Wouldn't that be nice?  Suppose the two button cells powering the Arduino board last a year.  That's not too bad.  Who knows they might last a lot longer than that.  You can use a bigger battery to power the Arduino board if you want.

MileHigh