Wednesday, July 10, 2013

Wizard Report I

It works.

We're in tech, opening this weekend, so I can't spare much time for detail.

The eponymous "Wiz" is wearing a coat with RGB LED strips along the lapels and 3W RGB's in the shoulders, feeding into a small festoon of cut-end light pipe.

Because of lack of development time and budget, his controller is an Arduino, with a Seeed Studio XBee shield attached.  To allow the micro to control the 2-3 amps of up to 12 volts required by the various lights, there is a separate driver board.

CPU, driver board, and an 8-pack of AA rechargeables are each in their own pocket sewn into the back of a vest he wears under the coat.  It worked.  He was able to move, the lights looked good (and bright!) and we could control them from the back of the theater.

Here's the only detail I have time for today; a little "what are the differences between these pictures?" exercise.

Driver board being built:

Driver board in finished form:

Well, besides the Altoid's tin, there are a few subtler (but very important!) changes.

The high side of the constant-current power drivers are now on an independent bus, instead of being tied to the positive lead of the main power supply.  (That gap in the board was to put a 12v DC-DC converter for the 12V LED strips.  Or I could have tapped the battery twice to put 9V across the constant-current drivers.  But in the end I went with simple; a 12V system bus).

And there's an even subtler fix:

The lads and lassies in Singapore assembled one of the constant-current drivers incorrectly.  I didn't realize this until after I'd blown out the red channel on one of my Cree.

Incidentally, some people recommend removing the diode rectifier array completely; they claim it causes RF noise.  I haven't had a problem with the circuit yet.

And that is actually the most important part of this.  Despite the Wiz's microphone being patched into a driver circuit for nearly ten meters of LED strip, and the poor actor being draped with high-amperage PWM circuitry, the Sennheiser wireless body pack has performed without issue or extra noise.

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