First time PC board design success (LED cabinet / closet lighting)

Though I’ve designed a PC board for my own production using a toner-transfer etching resist and no holes drilled, I haven’t actually designed a board before for actual commercial production. It’s rather tedious getting everything right the first time, but I managed to make it work.

I was recently playing around with some of the smaller Cree LEDs which are designed for lighting use (in this case, the CLA1B-MKW-XD0F0E83 [pdf] — these are about 12 lumens) and I happened upon an idea for a simple but very useful project. It occurred to me that I would like a little bit of light in the cabinets and closet in our hallway at home without having to turn on an adjacent room light or the crappy wall-mounted light at night. I prototyped a neat little 1.5 volt driver using a Diodes Inc. (formerly Zetex) ZXSC380 [pdf] — this is a better alternative to that “joule thief” circuit that has been going around for some time — and decided that it was sufficient illumination for the purpose. It should provide about 20 hours of operation off a AAA alkaline battery too.

So, after hoping to be able to do something more clever with a low quiescent current and low-voltage hall effect sensor, I gave up and used a SPDT reed switch (the most expensive component in the whole thing at $2.89 each!) so that when a magnet is close to the board, which is mounted just inside of the top of the door opening, it turns off. I expect won’t have to change the battery for years. The magnet is a 1/4″ cylindrical magnet glued in a 1/4″ hole in the door with Gorilla Glue.

I was happy with the price and quality of PC boards from OSH Park, but I certainly wish there was a faster turnaround way to get PC boards made that was also cheap. I did the design with Eagle CAD, which I’d used before a few years ago — but not where I cared about all the layers (copper, drills, holes, solder mask, etc.) I could have gotten the silk screening done better for some of the parts I created outlines for, but it works.

Closet light in operation

Yes, it’s slightly crooked, and it only seems dim with the iPhone flash on.

I’m damned impressed with some of the LED lighting products out there — the better CRI warm white parts are indistinguishable from incandescent bulbs to me. The next thing I’m working on is a lightweight clip-on LED book light for reading in the dark without being too bright. Things are slightly complicated in that I intend to make it USB rechargable, and to make things mechanically neat, I plan to use the Atmel QTouch stuff for the on/off. This will also allow some tricky user-configurable brightness without a tiny trimmer pot, since I know my wife will want hers brighter than I’ll want mine.

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