LED work lamp

[ADDandy]

so i have one of these lamps but the bulb is burnt out, so i picked up some LEDs from sparkfun, and want to modify it to use them instead of the florescent tube it normally uses.

The first thing i need to build is a constant current power supply (adjustable) between 500-850mA, at approx...15V.
i'll post more plans after my final.

[FingerTech]

Does it need to be that complicated? Just get a wall adapter and use the proper resistor to limit the current. I'm currently building a 600 LED array for Stealth Web Designs (their new sign) using a simple 48V power supply.

If your LEDs drop 3.5 volts and have a 30mA max rating, and you have a 12V adapter:
3 LEDs x 3.5V = 10.5V
12V - 10.5V = 1.5V
30mA = 1.5V / R, R = 50 ohms (47 ohms is a common resistor)
So you will have 3 LEDs and a 47 ohm resistor in series, and you can parallel as many of those as you need. The wall adapter needs to be able to supply 30mA x #series.

Here's a simple way to visualize it: http://led.linear1.org/led.wiz

[ADDandy]

muahah, These are my LEDs i have 4 of them. they are rated for 3.8v at 850mA, max current is 1A.

[FingerTech]

Nice! Careful you don't point it at yourself or you might start on fire.

[Tetragrammatron]

Speaking of lamps (with magnifying glasses)...anyone know a good place to get a solid cheap one? I've seen the ones with aligator clip arms that can hold a circuit in place while you work on it and don't know whether to go with one of those "all-in-one" solutions or go separate.

[ADDandy]

I think it wouldn't be too much of a stretch to just BUILD our own lamps. Once we have the lighting part down, we can find a magnifying glass, build a bracket for it that accommodates the lights, mount that on a moveable arm (salvaged from one of those desk lamps). and i think we are golden?

[rsilk]

Oh yeah, totally easy. Start with a $10 ikea desk lamp (like http://www.ikea.com/ca/en/catalog/products/20370383), mount the magnifying glass to it, and make a donut-shaped PCB to hold the LEDs. The trick is to find a decent magnifying glass on the cheap.

[ADDandy]

How large of a PCB can you mill on your CNC machine ryan? could we also use the CNC machine to make the housing for the magnifying glass?

[rsilk]

It should do up to 12" by 12" pieces easy enough. The flatness of the working surface starts to become an issue at some point, but there are workarounds. What I've done in the past is just mount a piece of wood to the table and shave the top off it with the mill to true it up. Easy to do, just takes a while. You could also etch the board and I could route the outline, but that's messy. It'll do most of the work for the housing, but won't be able to cross-drill any mounting holes or whatever. That'll have to be done manually after.

[DigitalOSH]

If you do this Andy, can you please document it in its entirety? And bring it to the meeting in January?