Tuesday, 29 April 2014

LED shades

A quick weekend project that got out of hand was my LED visor/shades idea. It all started because I found a load of 3D glasses in a drawer and thought they'd make cool LED glasses. But I couldn't design a circuit small enough to make a decent sized LED matrix in each "eye" (and simply dumping an 8x8 grid and only using up about half the available space in each lens seemed a little naff).

Then Jason suggested using some WS2812 RGB LEDs. I even got a reel of the 5mm square SMT versions from him and planned making some shades. But those were 6-pin jobbies, and I since found some easier-to-use 4-pin versions, and designed the entire project as a single, large, video-screen-as-a-visor.

But now I've a project that's designed, using components I don't have, and an idea that isn't what I originally wanted (which was, at the very start, to re-purpose some old 3D glasses) as well as a reel of SMT LEDs, not doing anything. Time for a re-think!

While, originally, I liked the idea of a "video screen" on the shades, I was also limited to single-colour LEDs. These WS2812 LEDs, however, are not just RGB, but support different levels of red, green and blue: so instead of just red on, green on, blue off to get yellow, it's possible to have red 100%, green 50% and blue 0% to get a nice orange-y colour. These LEDs support a wide range of colours - so who cares about pixellated video displays? Let's just make some funky colours!

Here's a single lens, using the 6-pin versions of the LEDs.
From reading on the 'net, these particular ones are tolerant of up to 6v on both the Vcc and Vdd (supply for the LED and the supply for the controller logic). Which means the extra 150R resistor, and a current limiting resistor on the LED supply shouldn't be necessary. The smoothing cap can go on the power supply to the entire matrix (or perhaps a range of different valued caps) meaning we might just get away with a matrix of just LEDs on a single PCB.

Here's a design I knocked up. It's using a 0.25mm trace to squeeze between the pads of the 6-pin LED. I suspect it'll be a nightmare to solder on a homebrew board, so I've also got some UV-curable solder resist ready to try out, when the board is etched.

This same design can be used for both lenses of my 3D glasses, and this particular design fits snugly into both. The through-hole connectors allow the two PCBs to be connected together via just three wires, while the other end of the circuit can be connected to the MCU which will do all the fancy data controls to the LEDs (and the power/ground supply from the battery operated "control box").

As it's already late, there might just be another trip down to the BuildBrighton Hackspace tomorrow evening, to try the circuit out - maybe with just three or four LEDs to begin with. But if it works with just a few LEDs, the rest of the board already has the rest of the circuit to get an entire lens working.

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