To run a LED from single 1.5 V, 1.2V or in particular largely depleted batteries, the famous Joule Thief circuit using a coiled toroid is great.
However, when salvaging the solar cell and battery from a cheap solar garden light to make a charging circuit, I realised the electronics are in fact a simple LED driver. The only part involved in the charging is a diode. So I took a new diode for the charging project and used the complete little circuit board as a Joule Thief for a cyborg zombie.
I used solar garden light bought in a package of 4 for 10 euros at [www.conrad.be Conrad] under nr. 572759. If you happen to have another use for the solar cell, on-off switch and battery, as I do, this comes very cheap for LED + driver circuit. You can simply cut the wires from the solar cell and just leave them like that. Replace the battery with the one of your choice (or keep the one from the solar garden light) and you're ready.
The circuit from the solar garden light is bound to be at least somewhat more efficient than the famous three-parts-joule-thief. The latter is great with almost dead batteries, but so is the solar garden light circuitry. Tests show it works till the battery voltage drops to about 0.6V. While toroid three-parts-joule-thieves are reported to go to 0.3 V, the ones I managed to build mine also need about 0.6 V.
For the cyborg zombie I cut the wires to the battery and fitted them to a connecting block. As the wire connections on this kind of circuit boards is quite fragile, I fixed the connecting block on the back with hot melt glue. You can leave on the switch and its wiring and glue it to the assembly in the on-position. This way no soldering is required. Of course you soldering a little bridge on the printed circuit board, replacing the switch.
To make a cyborg eye, I desoldered the led, ran the legs through a button and resoldered it on the printed circuit. Because this way the cyborg zombie misses the cool toroid-thingy, I first left the complete circuit on the outside of the zombies face, which is pretty cool to. However as the sharp edges are not very child-friendly, I implanted the board, leaving just the LED + button outside.
The cyborg zombie is an entry in Halloween Contest, so please check it out, and if you like it, do not forget to vote Nomember 9th and 15th 2009. Thanks!
However, when salvaging the solar cell and battery from a cheap solar garden light to make a charging circuit, I realised the electronics are in fact a simple LED driver. The only part involved in the charging is a diode. So I took a new diode for the charging project and used the complete little circuit board as a Joule Thief for a cyborg zombie.
I used solar garden light bought in a package of 4 for 10 euros at [www.conrad.be Conrad] under nr. 572759. If you happen to have another use for the solar cell, on-off switch and battery, as I do, this comes very cheap for LED + driver circuit. You can simply cut the wires from the solar cell and just leave them like that. Replace the battery with the one of your choice (or keep the one from the solar garden light) and you're ready.
The circuit from the solar garden light is bound to be at least somewhat more efficient than the famous three-parts-joule-thief. The latter is great with almost dead batteries, but so is the solar garden light circuitry. Tests show it works till the battery voltage drops to about 0.6V. While toroid three-parts-joule-thieves are reported to go to 0.3 V, the ones I managed to build mine also need about 0.6 V.
For the cyborg zombie I cut the wires to the battery and fitted them to a connecting block. As the wire connections on this kind of circuit boards is quite fragile, I fixed the connecting block on the back with hot melt glue. You can leave on the switch and its wiring and glue it to the assembly in the on-position. This way no soldering is required. Of course you soldering a little bridge on the printed circuit board, replacing the switch.
To make a cyborg eye, I desoldered the led, ran the legs through a button and resoldered it on the printed circuit. Because this way the cyborg zombie misses the cool toroid-thingy, I first left the complete circuit on the outside of the zombies face, which is pretty cool to. However as the sharp edges are not very child-friendly, I implanted the board, leaving just the LED + button outside.
The cyborg zombie is an entry in Halloween Contest, so please check it out, and if you like it, do not forget to vote Nomember 9th and 15th 2009. Thanks!
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The whole set up is known as a buck charge inverter, The device is in fact a tiny inverter or oscillator feeding the small inductor, its the back emf, or the collapse in the magnetic field within the inductor that lights the LED, and NOT the direct DC from the battery.
The circuit will still light an LED as long as it can oscillate, which would be down as low as 0.6 volts, and still feed the same amount of power at 6 volts, the amount of power available is determined by the size of the inductor. I have 5 high power LED's running quite happily at full brightness on 0.8 volts
Sourcing the 5251F is difficult unless you want 10,000 of them for your next project. I have details of a similar set up that uses only 3 components, transistor, resistor and a simple hand wound coil, very easy, and another circuit that can drive 30 leds with about 10 components.
I've been trying to find an efficient auto off in light option out there with NO luck. They take too much voltage. I just wanted to upgrade this solar light to lithium, which doesn't need the boost, but I still needs the auto off. (Solar direct to protected cell.) Finding a circuit that doesn't eat the voltage has been impossible.
The convenience of the small all in one package makes it super easy to add to several projects since all you need is two components plus the LED.
I use the "joule thief" circuit similar to the one shown in my other "cyborg zombies": http://www.instructables.com/id/Cyborg-zombie-feeding-on-quotdeadquot-batterie/
For a coil with a single winding, a typical simple Joule Thief circuit has two transistors, a few resistors and a small capacitor of about 220 to 1000 picofarads. You can see a schematic of it here. It would be best to make this two transistor circuit, because you may never find the four legged IC that is in the circuit in your picture. I've seen a whole lot of ICs, and I can't ever remember seeing one like that. It's probably a custom IC made especially for the company that builds solar lights. The coil that's in your picture (it's not a resistor) looks like it's 100 microhenrys. I make air core coils, and they work okay. Here's one I made recently.
Of course on ebay you could by the solar lights for about $1.5 and it saves you the trouble of finding the components. They come with batteries that are half of what they are rated, ie 600mA is really 300mA if you are lucky.
1000 picofarads would not work with this circuit. 330 is the most. That is dim, but last days and days. 35pf is very bright and last about half the night. (dies around 1am)
http://www.megaupload.com/?d=ZXGXUAF9
I think the way to go is to buy a completely assembled circuit board for a flashlight. Here is one. It works with a single AA cell, and will drive several LEDs, but the battery isn't going to last all night. If I want to drive a single LED with limited current, a simple 1 transistor joule thief with a 2N4401 should draw about 75 mA, and run for several hours.
http://www.instructables.com/id/Make-your-own-solar-powered-led-string-lights-/step4/Lets-start-putting-the-circuit-together/
For a coil with a single winding, a typical simple Joule Thief circuit has two transistors, a few resistors and a small capacitor of about 220 to 1000 picofarads. You can see a schematic of it here. It would be best to make this two transistor circuit, because you may never find the four legged IC that is in the circuit in your picture. I've seen a whole lot of ICs, and I can't ever remember seeing one like that. It's probably a custom IC made especially for the company that builds solar lights. The coil that's in your picture (it's not a resistor) looks like it's 100 microhenrys. I make air core coils, and they work okay. Here's one I made recently.