Wednesday, August 7, 2013

LiPo and Buck-Boost and Xbee and Cree, These Are a Few of My Favorite Things...

I'm in production, working a 30-hour week for show calls alone (plus ongoing repairs and maintenance, meeting on the next two or three shows, etc.)

Plus I've really fallen behind on such things as house cleaning and car repair.  Plus finances are still not good, meaning I need to concentrate on work that pays instead of long-term development.


An upcoming show is going to use a lantern.  They seem happy to handle it themselves -- didn't even think of asking me -- but is a good excuse to continue the development I started back with my BlinkM experiments.  Especially since The Wiz showed I could make a battery-powered remote-controlled rig that PWM'd multiple channels of high-power LEDs.

The BlinkM board from ThingM is very cute; it combines a "Piranha" LED with an ATtiny controller.  They package it with an easy-to-use software that uses an Arduino as a programmer (or you can use another USB to serial converter, like my own favorite USBtiny ISP from Adafruit).

But it is underpowered for stage use.  Especially if you intend to actually light part of a scene with an oil lantern hanging in a barn, or a storm lantern in an actor's hands -- or something more unique like a glowing crystal ball or Wizard's Staff or whatnot, we really need to reach for the power of the Cree; several options in 1W LEDs, single-color and RGB.

Unlike the mere 30ma a channel of a Piranha, though, the 350ma of a Cree can't be switched by a naked AVR.  Plus the power-hungry nature of these things means you really don't want to be throwing half your battery life into cooking a 2W current limiting resistor.  The best option is an actual current-regulated supply, better yet, a buck converter that trims the voltage down to a useful level without throwing half the power away as heat.

The reason for all this complexity, of course, is that with a bulb and a wire (or even a high intensity LED and a wire) you are limited to static display.  With the embedded AVR, you can flicker like a candle, or pulse or change colors.  You can dim up and down instead of the light switching instantly to full power, which also makes for a more realistic effect.  You can adjust the color of the effect, and the intensity of the effect, without having to wrap gel around it.

And this level of control can be achieved remotely.  In the case of the WIZ's coat, via a laptop in the booth.  The simplest link (and one of few with the range for theatrical use) is the XBee modules.  Unfortunately they are also not that cheap, and have other electronic requirements.

Which brings me to the tangential "Duck Node" concept; small battery-powered XBee-enabled devices that can either be used to sense an actor's motions or other commands, or reversed to control an effect -- such as the battery-powered high-intensity lights we are talking about.

What I want to build right now, then, is a prototype lantern.  For the upcoming show, it would work just as well with a mono-color LED, a switch on the side so the actor controls it, and not even a flicker circuit.

But I'm going to give it the full bells and whistles; RGB LED, and full remote control.  The only trick at this point (since I have all of that working now on stage in another form factor) is getting it to fit inside an oil lantern.

If the prototype works out, though, I'll be able to custom-design the next circuit to be printed instead at a fab house.  And then I might actually have something to bring to the next Maker Faire....

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