I have a desk with a shelf above it, so I made a light strip I could put on the bottom of the shelf to light my desk area. I had some LEDs sitting around, but no simple way to make a circuit board for them, so I make a wooden housing to hold the LEDs and make a simple lighting strip. I made it at techshop in menlo park (http://www.techshop.ws), using some tools in the woodshop and basic tools like the soldering iron.
Pine board (section of a 1x12, about 19 inches long)
25 white 5mm LEDs
soldering iron (and solder)
clamps and glue
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Step 1: Wooden Housing - Blade Depth
For the wooden housing, I basically created a U-channel by cutting a large groove near one edge of my board, then cutting the whole thing off from the board.
To do this, I first removed the blade guard assembly and lowered the blade so it wouldn't cut all the way through the wood. (My groove was shallow enough that the LEDs are completely contained- if you want them to stick through the holes, you can make a deeper groove with less material remaining.)
Step 2: Wooden Housing - Cutting Grove
Once I'd set the blade depth, I set the rip fence so that the edge of the board was about 3mm past the edge of the blade, and cut a groove. I then moved the fence over a bit and cut another groove, repeating until the groove seemed big enough to house the LEDs (about 3/8 of an inch). Then I moved it a bit further over and brought the blade up high enough to cut all the way through the board, and cut it off.
I also cut one a very thin strip of wood that I'll use later to cover the back of the assembly.
Step 3: Wooden Housing - Drilling Holes
The next step was to use the drill press to drill holes in the housing for the LEDs to shine through. Since the LEDs are 5mm diameter, I used a 5mm drill- it's a tight fit, but the wood has some give, and once the LEDs are in, they'll stay put.
Start by drawing a pencil line down the center of the housing so you can line up all your holes.
A simple jig keeps the spacing even: clamp a piece of wood to the drill press table and put some kind of peg in it, a certain distance from the drill bit. A dowel would probably be ideal, but I just used a screw. After I drilled the first hole, I put it over the peg and then drilled the next one, then moved the 2nd hole to the peg and drilled the 3rd one, and so on. Just line the drill bit up with the center line to get a nice row of evenly spaced, centered holes.
I used 25 LEDs, and my housing was about 19" long, so I tried to space my holes 3/4 of an inch apart with a little space on the ends.
Step 4: Electrical - Planning
Again, be careful with the electrical wiring, since we're using straight wall current.
The basic idea here is to put all of the Light Emitting Diodes in series along with a current limiting resistor, and then connect that to the alternating current from the wall. It may flicker a bit because as the current alternates between negative and positive it will only light up on one side of the cycle, but it's one of the simplest ways to do things. I just needed to figure out what resistor value to use so we run the right amount of current through the LEDs.
Ideally, I'd have spec sheets for the LEDs that list the appropriate voltage and current, but I'm re-using some that were pulled out of another project, so I don't have that handy. Looking at the specs for a similar product (http://www.superbrightleds.com/moreinfo/component-leds/5mm-white-led-30-degree-viewing-angle-18000-mcd/256/), the current rating is about 30mA with a 70mA peak, and the voltage drop is around 3.4. My multimeter actually has a diode setting, but it won't measure the voltage drop on these. Just to check, I powered up one LED to see how much voltage was dropping across it; it was just about 3v.
Since I plan to wire 25 LEDs in series, I'll be dropping 75 volts total. Assuming the peak wall voltage is 125v, the current limiting resistor will have up to 50 volts across it. Conveniently, a 1kOhm resistor would give 50 milliamps at 50 volts, which is probably a reasonable peak current for the LEDs.
peak wall voltage is actually closer to 170, so peak current is higher than intended
It's important to make sure the resistor is big enough to handle the expected wattage.
Step 5: Soldering
Having selected a resistor, I soldered the LEDs and resistor into one long chain. Since my LEDs were pulled out of another project, their leads had been clipped short and I had to solder bits of wire in between them; normally you can just bend the leads from one LED over to meet the other one and cut them to fit.
I placed the LEDs in their holes upside-down so they'd be spaced properly and easy to get at. Then I triple-checked that all the flat sides were facing the same way.
IT'S CRITICAL THAT ALL OF THE LEDs ARE LINED UP WITH THEIR FLAT SIDES FACING THE SAME WAY, since diodes only let current flow in one direction.
Step 6: Done Soldering
Once the LEDs were soldered together, I gently removed them from the outside of the housing.
Step 7: Place LEDs and Resistor in Housing
Next, I flipped the housing over placed the LEDs in, aligning them with their holes. I didn't want to press them all the way in yet; just gently seat them in their holes so they stay put. Then I solderd the resistor onto the end.
Step 8: Cord and Backing
Once the LEDs and resistor are connected, I got a piece of lamp cord. I cut one conductor longer than the other to up with one end of the wire at each end of the housing. Then I soldered this to the LEDs and resistor.
Once everything was hooked up, it was time for the smoke test. I used an outlet strip with a circuit breaker which would shut off if there was a problem with the wiring, but luckily it worked fine.
Having verified that it works, it was time to unplug it and finish putting it together. I pressed the LEDs firmly into their holes, and closed up the back by gluing on the thin strip of wood I cut earlier on the table saw. Otherwise, tape or some other insulator would work to cover the back and ends.
Step 9: Success
Now I have a simple LED powered wooden lamp that I can mount under a shelf or wherever I need more light.
There are several things you could do to improve on this design, like adding a base to make a desk lamp, using a DC power supply, adding colored LEDs, etc. Have fun!
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