Tuesday, July 16, 2013

Wiz Report II

So.  My first wearable.  We've learned a few things over opening weekend:

-- You can punch a 2.5 gighertz signal through metallic brocade, an actor, and a hundred feet of air, but it takes power.

-- You can dance and sing with an 8-pack of AA batteries on your body.

-- An Arduino, an XBee radio, and a meter of PWM'd LED strip doesn't create enough noise in a good wireless microphone to matter.

-- 60-LED-per-meter RGB is actually overkill.  We were afraid the costume wouldn't be bright enough to be visible over stage lights.  It is so bright I'm thinking of turning it down! 

-- Client-side works, and does permit more elaborate/faster animations, but server-side is more flexible.

-- Digital would be better.  Soldering all those leads for analog RGB was no fun.  Also, the leads on the RGB strips keep coming loose.  Digital is only a few bucks more -- and allows even more elaborate animations, too!

So that's the thing.  This is actually turned down a bit.  The look is simple; LED strips stitched along the edges of the lapels, and 3W LEDs under the shoulder things.

The electronics are in pockets stitched to a vest, which hangs loosely inside the jacket so as not to disturb the hang of the jacket.

Here's the signal chain;

A Processing ap allows the operator to click on one of several programmed "looks" (most of them are animations; pulses, flickering, color swirls).

Processing spits out a serial word to a SparkFun USB adapter holding a Series 1 XBee Pro.

The signal is picked up by a matching XBee on a Seeed Studio mini-shield, and sends the serial word on to an Arduino via Soft Serial. 

The Arduino, running in a form of RTOS, routes through one of several programs to output the three PWM signals.  Which are basically lifted from the "Blink" code I wrote a while back.

These are sent to a second box containing the switches and drivers; Tip120 power darlington transistors switch the LED strip, and "MR16" type constant-current drivers switch the 3W "Cree" LEDs.

Then the wires all come out the back of the neck, under the collar, and are routed to each lapel and to the shoulders.

On each shoulder, a "Cree" with an improvised heat-sink of aluminium channel pushes light into a half-dozen random lengths of plastic light pipe (bought at SparkFun, and probably the most expensive part of the costume electronics).

The final effect is QUITE bright.  (The picture to the left is under work lights.  I had to stop the camera down considerably.)

We only use it for "So You Wanted To Meet the Wizard."  At the top of the song, it glows green (shifting subtly between yellow-green and blue-green).  For the soaring "B" section, it goes to a shimmery blue.  And at the end of the scene, ("I have spoken!") it goes to a rapid mostly-red flicker/flash.

During the dialog scene we're running it at an extremely low setting (analogWrite(green, 8)) just to give the costume that hint of sparkle.

And of course we black it out at the end of the scene.

Next time I do something like this, I'll use either an Arduino mini or similar, or a proper wearable like the new Flora.  Although XBee support is a little minimal on those options.  I'll also go with either AAA power pack, DC-DC boost converters and a smaller set of batteries, or perhaps liPo.

I'll also probably skip the driver board.  You do need a switch for analog strips or the Cree, but for many costume applications Flora pixels or digitally-controlled LED strips are plenty.  And those have internal drivers; all you have to do is supply enough amps from your battery pack.

But for this show...since I'm taking the CPU back after the show, the total cost of the electronics was about a hundred bucks.

This show was very much thrown together during Tech.  And I haven't had a chance to go back and tidy up yet.  Here's the Vox Box, as used in the show; propped up on top of the amp cabinet by the snake, plugged into a Behringer micro-mixer to boost the audio signal it is getting.

Since the lead's microphone is fed into a dedicated mix bus for this effect, I can adjust the response somewhat from the mixing board during the show.  The one thing I haven't been able to do is set the lower trim; that would involve running backstage to turn a trim pot inside that Altoids can there, during the song.

And a good thing I put the heatsink on.  I measured a bit over six meters of platform, and purchased two five-meter rolls and a power supply designed to drive one roll worth.  Then they decided they wanted to extend the LED strip along the ramps leading up to the platform in question.  That makes it the full ten meters, and is well above what a TO-220 package transistor wants to dissipate without a heatsink. 

Soon, though, I will change over to Power Mosfets, which have a smaller voltage drop and hence run cooler (as well as producing brighter effects).

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