Making a LED Light for computer table

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Rifter

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May 21, 2002
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Ok here is the deal, I Would like to get back into electronics(havent touched a soldering iron in 10 years) but i do know the basics still and im sure the rest will come back with time, ive been going over some of my old text's. What i want to know is whats the best way to drive 5-10 white LED's? im assuming i'll need that many to get the light output im looking for, something a little brighter than a innova X5. This will be powered with whatever i can come up with but it will be from a AC source obviously since its for my house, i have a bunch of AC/DC adaptors laying around with differnt voltages/current and will use one of them, or maybe a computer power supply depending on what voltage i end up needing. Im looking for overall costs and wether or not anyone has done something like this before and has some circuts i could look at. And before someone says go out and buy a light i want to get back into electronics now that i have time and thought this would be a good starting project, since its simple. So what LED's do you guys reccomend, preferably ones that dont get to hot. And where do you buy yours from? Sorry for all the questions but im trying to get back up to speed on things.
 
no no no, im looking to BUILD a lamp, my computer desk looks like hell to begin with i dont care if it looks ghetto but i want to actually build it pretty much from the ground up. Like aproject to get me started into electronics again.
 
You're just looking for a project right?? Why don't you post a pic of your desk and we can give you some LED related ideas...Maybe a LED array all across the back or somthing, does it have glass? We could light up the glass with colored LEDs activated by a motion sensor (You want to get back into electronics right??)

anyway...I am just making suggestions, I don't know what you want (A light for your desk right but)

HEY look, a PANDA bear!
 
panda bear? anyways its a simple wood desk, no glass, one level no shelves nothing, was build by my grandpa out of a old door with some 3x3 for legs. I was thinking of mounting it on the light fixture thats above the desk now, its one of those things that comes out of the roof and has like 3 x-mas light bulbs in it, thats why i want more light output, this thing is not even as light as a mini mag, will take pic later of the fixture and post it.
 
Well, if ugly doesn't bother you, all you need is one of those matrix breadboard PCBs, and just solder a bunch of white LEDs to it (say 10). Then you can connect them in parallel (easy if you line them up facing the same way).
After that, all you need is to calculate the resistor value for the current you want to run them at, based on the voltage supply you plan on using.
10 LEDs at say 40mA each means 400mA, so you'd want a supply which can handle that current. Then, work out the resistor value based on the supply voltage - LED voltage / current.

Once that's done, you could mount it in a little box with a perspex lid, or just leave it out in the open, and maybe make some kind of arm our of wood or whatever. Mount it on the end of the arm, clamp it to the desk, and there you go. Ugly but functional. If you make an arm and use a G-clamp to fix it to the desk, it should project the correct 'DIY' feel to put you in the mood for electronics...
smile.gif


Graham
 
Not sure about online - I've never ordered small components like this online (I live 30 minutes away from a huge electronics shopping district..), but a quick look around found this at Radio Shack, which would do the job nicely (it is even 2 boards, so you could make 2 of them...) There are other similar boards there, if you want to use your imagination..

For the LEDs, there are other places online like Mark Hannah Surplus or The LED Light. I'm sure there are others which people here would recommend.

Graham
 
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Graham:
Well, if ugly doesn't bother you, all you need is one of those matrix breadboard PCBs, and just solder a bunch of white LEDs to it (say 10). Then you can connect them in parallel (easy if you line them up facing the same way).<HR></BLOCKQUOTE>

I would strongly advise _not_ to run the LEDs in parallel. See these discussions:

Question on mA draw

Linear regulator or Buck regulator

Since you are operating from mains power, you have lots of voltage available. So a simple circuit is to put all of the LEDs in series using a single resistor and power supply of suitable voltage.

If, because of the parts you have available, you decide to run the LEDs in parallel, I strongly recommend that you put an individual resistor on each LED, to better balance the current flow. With a single resistor shared across a bunch of parallel LEDs, the LEDs with the lowest voltage drop will 'hog' the current.

Finally, if you can arrange to heat sink the cathode, you will improve efficiency and LED life. This is easier in a parallel arrangement, because you can connect all of the cathodes to a single large heat sink.

-Jon
 
Jon is correct, of course - I was being lazy (slap on the wrist...), since parallel is probably a bit easier to put put together on a simple breadboard PCB.

If you run them in series, it means the supply can be a lower current one, too.(as long as the voltage is high enough - another reason I considered parallel, since 10 LEDs would mean a 36v plugpack - not many of those about..)

Graham
 
hmmm, i do have 2 20V/1000ma AC Adaptrs laying around, i could make 2 clusters of 5 or even just use one adaptor and step the voltage up, i should still have enough current, will have to do some calculations. What type of LED's are best for general lighting? and whats the cheapest place to order online.
 
I'd say that you should just use one of the 20V 1A adapters, and then use strings of LEDs to use up about 15V-18V, and linear regulators to drop the last little bit of voltage.

As far as where to get the LEDs; the Nichia white LEDs are quite popular; if you search on this BBS for threads on where to buy Nichias, you will find some useful links.

Currently the Luxeon light sources are the most efficient white LEDs, and per unit light output they are cheaper than the Nichia units. However the bare emitters cost $12 each; depending on your power requirements, you might only use one of these beasties; but if you want to spread the light out you would need several devices, and that starts getting costly.

Devices which have not been discussed much on this BBS are the 'Superflux' LEDs by Lumileds. You can find information on these LEDs atSuperflux Index

I am quite partial to the Superflux Red and Amber units, but I have never used the white units, and don't know how they would stack up against the Nichia units. The Superflux LEDs are sold through Future-Active Electronics.

If you use the Superflux type LEDs, I can sell you pre-made double sided PCBs which are about 0.5" by 0.75", with holes for mounting to something else, solder holes for the wires, plated through holes for the LEDs, and lots of copper area to act as a heat sink. Each PCB holds a single LED, and costs $0.50.

-Jon
 
Hello Rifter,

I make some simple LED lights which are available from a few on-line dealers. With similar intentions as yours, I looked into the various LED's available and determined that the Nichia NSPW312BS provided the best and most even light dispersment of all of the 3 and 5 mm LED's available. The 3 mm package also allows for tighter clustering of light sources.

You can see a non-professional display of these lights at:
Tri-Clusters and 9stars

I would be happy to provide you with any of the loose LED's, rubber disks or metal housings that you see on the sight. I use a simple resistor in series and underdrive the LED's but you could use the rubber disks to hold and present the LED's and devise whatever circuit you wanted behind the disk.

For the heck of it, I made one 9star with 3 red, 3 blue and 3 green LED's I put a seperate pot on each color series so I could dial in various color combinations. Unfortunately, the red Toshibas couldn't compete well with the blue and green Nichias that I used.

If any of these components are of interest, let me know.

Don
EDIT [ I just realized you are in Canada and I have been burned by VAT with Fed-Ex shipping as well as lost packages via Canadian mail. I'm sorry but I guess this offer has the condition that I send any items to a US destination] SORRY
 
Ok just ordered some white LED's, i got the Nichia white LED's. When they arrive I will start playing around with them. Also i decided that series would be better so that means im gunna need 36 volts right? and the current reccomended is 20ma per light, so is 200ma ok or should i go higher.
 
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