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I got sick of the area under my workbench shelf from being dark, so I started to look at lighting options for this ~25cm high space that is eternally shielded from my workbench light.
Light bulbs and CF bulbs were excluded from the start, as they're way too bulky for this space. I needed something slim and low profile. A CCFL tube was employed for a while, but didnt quite have the brightness and diffused illumination I wanted. But then whilst eBay browsing I struck gold - white LEDs!
Next, I cut grooves in the board for the wires - I wanted this to be low profile with just the LEDs visible. Exposed wiring is messy and dangerous on an electronics bench. My trusty Dremel clone did the job amicably, although the friction made a lot of smoke, but didn't permanently discolour the board. Photos below shows this in action, as well as the final result after all the grooves were cut:
Inserting the LEDs was the next step, and pretty time consuming. Each LED had its wires bent almost 180 degrees, then pushed into the hole, looking out. The wires were then bent to meet its neighbour's legs. Care was taken to ensure all LEDs were the correct polarity. The photos below show this:
Soldering the LEDs was a bit tricky. I clipped the legs to be just short enough to overlap the neighbouring LED, then carefully soldered them flat against each other. This had to be such that the legs could be recessed into the grooves I cut. Finally I got this done, and ran main bus wires along the top and bottom row so that each chain of 6 was in parallel.
It was time for first light. I grabbed my bench PSU and wound the voltage nice and low. Hooked up the LEDs and gradually rose the voltage, and they all lit! Eventually I rose it till the current hit 380mA, and I had a massive array of white LEDs. (MAWL). See below for what this looked like. I mistakenly drilled 7 holes in each row, seen here too, but these were filled later.
Sealing the LEDs was the next task, done using a tube of two-part plastic compound. Similar to Araldite, the two parts are mixed together, and after about 20 minutes sets to a rock hard compound (as opposed to soft epoxy). Using a blade as a spatula, I smeared it into the grooves, ensuring the wires were well recessed, then let it set. This is what it looked like while curing:
Once cured, I used a knife to scrape away the excess, leaving just filled grooves and otherwise smooth laminated board. Next I used some white hobby paint to finish off the job. The result was a MAWL, with somewhat hastily obscured grooves holding the wires, eventually leading out to the edge of the board for the power supply.
Powering the LEDs is currently done with a bench PSU, but I'm just about to add on a proper supply - basically a 24VDC wall wart, with an LM317T based constant-current circuit. Eventually I might also do a PWM based dimmer, but that's for a little later.Posted by Ben at July 1, 2007 03:11 AM