Thursday, 1 May 2014

LED Desk Light – n x n matrix – Je suis fini

Yay … I’ve completed the LED Desk Light 5 x 4 matrix!
That wasn’t so hard. Well … now that I’m sporting a bright shiny new pair of +3 reading glasses (for the princely sum of $15AUD).
The reading glasses made the soldering very easy. Much easier than the desk magnifying glass. I was finding that the focal length of the magnifying glass was too short, and so, the depth of field/operating space was much too limited. The reading glasses give me a much better nose to soldering iron length.
Anyway, enough of me whining about my aging eyes and on to the show and tell.
The main action takes place on the underside of the perf-board.
Picture 30
As I described in the previous post (here) the matrix is really just one parallel run of LED and resistors. I’ve linked the LED anodes with red jumpers and the resistors with black jumpers. The 2 pin header is at the top right of the perf-board and the series runs from there to the left, then down and to the right, down and to blah, blah, blah … as seen in the following image.
series direction
Soldering the jumpers on was a little bit of a pain, the distance between the leads is fairly small so a) stripping the wire was annoying and b) holding the jumpers in place with alligator clips was a pain. Still … all done now, I can move on.
Picture 31
The top side of the perf-board is much more attractive. All of those 5mm LED and their resistors all aligned nicely in a grid. Very nice and uniform. Just to the right, you can see the 2 pin header and the 2 pin Dupont connector that I made up for the 5.7V AC Adaptor. I’m pretty pleased with the adaptor modification. I may have to do a little re-work on the circuit to include a switch, but that can come later. You can also see how the resistors worked out using the paddle pop stick as a bending jig, and also in the horizontal alignment.
Finally, you want to see it all lit up, right? Well, here it is.
Picture 32
All lit up like candles on a birthday cake. It is quite bright but only has a 25o viewing angle. I’m thinking about making a project box with an opaque white cover to work as a diffuser. That should work.. I also need to think about how to mount the light on a stand so that it casts it’s light down (or up if I want). Again … later.
All up, I’m happy with the prototype and I’m going to start planning the SMT edition of the light. All I need to do is find some suitable (and cheap) components on eBay. On reflection, I think I’ll use the 0805 rather than the 0603 it’s enough of a difference in size to make it easier on me and still small enough to make it worth while.
Oh and … in case you are wondering, the perf-board is 50 x 70mm in size.

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