Project
27 LED desk shelf light with variable voltage controller
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Published
Feb 17 2012 by FaTe
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I said in my last project (see link above) that now my floating shelf was in place the last step would be lighting in some way. As I don't want a desk lamp taking up space or something big and clumpy hanging I decided to make my own (again).

For this lighting set-up I'm using 27 daylight LED bulbs which is more than enough on a single USB lead. All the LED bulbs are in parallel meaning they are not joined in a big row but each powered individually.
/media/Desk/shelf light/1-Plastic balsa ply
First job was to bond the plastic to the balsa-wood backing, the balsa provides a work surface while soldering so the plastic doesn't melt or deform, also wood dissipates wood better than plastic. I used UHU 300 Epoxy smeared across the sheet and then just using books and other heavy objects to bond them while it dried.
/media/Desk/shelf light/2-side rails
All the electronics sit on the top so it needs some space when against the bottom of the shelf. I added 2 ply wood beams each 1CM * 1CM * 38CM super glued and then a little Epoxy I had left over.
/media/Desk/shelf light/3-LED configuration
In total there are 27 LEDS, 3 rows of 9. Each LED is 4CM apart to give maximum spread and keeps a good bright focus with no dull spots in the middle, also I'm using also using a resistor per LED (BLUE|BROWN|GOLD).
/media/Desk/shelf light/4-marked out
Good planning is key so I properly marked out the area on the back and drilled the LED holes for the legs to pass through. That was 57 holes to be drilled lol.
/media/Desk/shelf light/5-LED resistor heat-shrink
Now each LED is mounted in place with its capacitor I used heat-shrink pipe to insulate the bottom of the LED and by pulling the LED up as I heated the piping it pinned the LED in place so no glue
/media/Desk/shelf light/6-earth insulation
Now because everything is powered from 1 USB lead I simply connected every LED negative pin leg to a rail and shared them all back to 1 point. To stop contact shorts I used black electrical tape over all the legs leaving only the positive pin legs out. Next I soldered 2 LED positive legs together in pairs on each row, then created connections between each pair to lead back to 1 point for the entire row. Once all the rows are soldered it was simply a case of running of just 2 cables to connect all 3 rows up.
/media/Desk/shelf light/7-mounted on shelf
I missed taking a picture but I installed a variable voltage control knob which simply adjusts the voltage allowed to pass through it by adjusting the knob (like a light dimmer switch). This goes between the LED positive connection side and the black switch you can see.
/media/Desk/shelf light/8-switch variable voltage knob
So I can now adjust the brightness of the LED rows and of course turn it on and off.
/media/Desk/shelf light/9-demo 27 LED on
I can see when I'm soldering now!!!
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