Broken electronic devices are a gold mine if you know what you are looking for, you can find lots of useful components that otherwise would end in the trash. Specially complex devices such as computers and laptops are the most valuable, you can obtain from fans, switches and LED's to replacements for other computers passing by lots of very useful spare parts.
In this instructable I will teach you how to build a power supply to power an LED stripe I found at a laptop screen, this stripes are used for retroillumination and they can need large voltages in order to be driven. I will also make a lamp out of it.
- Led stripe.
- Solid wire.
- ~1000 Ohm resistance
- PNP transistor. (I used a 2N2222)
- Old phone charger
NOTE: Most of these materials can be found easily if you have some broken or unused electronic devices around, I'll be telling you where to find this materials along the instructable.
Extra materials: (To make the casing for the lamp)
-1mm Aluminum sheet.
-4x wood screws
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The LEDs that retroilluminate the screen of the laptop are quite bright and don't need too much power. You can find them on most of the conventional LCD screens, usually at the edges behind the layers of glass and polarized filters.
If the screen it's shattered and looks sticky and covered in oil it might have a leak of liquid crystal, although it isn't toxic, gloves are recommended, specially if working with shattered glass to avoid cuts and splinters.
P.D: The screen I used was broken so it would have not been useful as a replacement or for another project.
We will begin with the LED strip, usually the connections to power it are very tiny and very close from each other. If you are good at soldering and have a surgeon's steady hand you will weld the wires easily, I didn't, so instead I drilled holes where the negative non etched areas of the PCB of each series were, then i removed the paint exposing the copper, passed the wires though the holes and welded them in place, joining them to connect the three series LED
I had to solder the positive lead to the tiny pin because the area of the positive trace wasn't big enough to make a hole.
Next we want to power it. This stripes usually have the LED's placed in series, mine has 24 LED's divided in three series of 8, this means they need over 20 volts to work !
To power it we'll be doing our own power supply by making a small voltage amplifier (aka. joule thief) out of, yes, you guessed right, more electronic junk.
Joule thiefs work accumulating a magnetic field inside a toroid, when it is saturated, the toroid becomes self induced, creating a voltage peak on the coil that surrounds it. This voltage peak allows to power the LEDs during a shoort period of time, but the speed at which this whole process occurs is so fast it seems the LEDs are constantly lit.
To build it we need a toroid, depending on the inductance (and mostly the material they're made of and their purpose) it will work or not, the ones that work are usually found at power supplies, big CFL's and old computers. We also need a ~1000 Ohm resistance (finding the correct one might take you a some time since there are hundreds of them, you can buy one for some cents). Then we need some thin and solid core wire and a PNP transistor (I got two 2N3904 from a mouse but I ended using a 2N2222 because it gives twice the output).
Warning: Depending on which devices you disassemble capacitors can still store a lot of power, old CRT TV's are usually a DON'T, power supplies can be also dangerous, make sure the capacitors are discharged. Always use gloves when working with such devices or when you see large capacitors.
After you've collected the materials we can proceed with the assembly.
To make the circuit first we want to wind the toroid, to do it, grab some solid wire and bent it by half so you wind two cables at the same time, tie one end to the toroid for convenience and start winding, try to cover the toroid completely, make sure the wire is tight and there are no cables laying above each other.
When finished, you'll have 4 cables coming out of it, 2 facing each side, grab one of each side (from a different cable) and join them, this lead will be connected to positive.
Take one of the remaining cables and attach a resistance to it, then join it to the base of the transistor (see pictures for reference), you can also use a small potentiometer in series with the resistor to regulate the brightness
The other cable has to go with the collector and the emitter of the transistor will go to negative.
The LED strip will be connected to the transistor, positive to the collector and negative to the emitter.
Toroids are quite a pain because they're very difficult to identify, each one has a particular inductance, if we don't find the correct one the circuit will be terribly inefficient. I had to test some of them, the first one, a small green toroid, made the strip to give off a very gentle light, and the ammeter showed 0.21 amps, way too much for such a low brightness. You should set up a breadboard and try every toroid by separate and by measuring the amps and the brightness determine the best, sort of trial and error.
I tried again with a medium sized and a large toroid, both scored 0.13 amps, with at least twice the brightness than the first one, since there was no difference between them I used the medium sized one for space reasons.
We can now test the circuit, it will work with low voltages like 3 or 2 volts, but I'm not a big fan of batteries, so I'll be using an old mobile phone charger, this should be perfect to power our circuit.
Connecting it at it's maximum brightness shows a current of 190mA, that means around 8mA per LED, the maximum is supposed to be at 10mA for this kind of LED's, so I'm more than happy.
To finish the lamp I wanted to have a stylish case for the LED stripe, so I carved a piece of wood with a Dremel aided by my homemade drill press, I made a straight line for the strip and a hole to place the joule thief. I've made the hole big enough to fit a switch just for convenience.
I covered the hole with an aluminum plate like I did with my decision box project, just mark the shape using the wood slat as a template, then cut it carefully, with a clamp, attach it to the wood and with a file remove the excess of metal. To put the screws, mark the points on the metal taking into account the screw's head diameter, drill the holes on the plate and then, using the plate as a guide, drill the holes in the wood.
To make the thing look more neat I also stained the wood with a protective gel stain and added some staples to hold the strip in place.
I also plan to add some magnets at the back of it so I can attach it to any metallic surface, and a hanger for convenience.
I hope my instructable has been helpful to teach you how to power this kinds of LED stripes and to make people realize they can do many things if they save their electronic scrap instead of getting rid of it.