bm2005: 16 10mm white LEDs, 9V battery wearable or serial controllable

This web page documents a board with 16 LEDs, individually dimmable running patterns or serially controllable
Board size: 3.00 x 3.00 two-layer, round with red soldermask

Project timeframe: July 2005; serial enhancements September 2006
Client: Leo Villareal
Webpage created: May 20 2007

Top view:

Bottom view:

(these pictures are of the serial prototype, hacked a bit.  Wearable production units are round with red soldermask for aesthetics.)

bm2005 (i.e. the blinky for Burningman 2005) is the second generation of the wearable LED blinkies for Leo Villareal / disorient.  (other years: bm2006, bm2004).  bm2005 is a circle of 16 10mm white LEDs, and is actually two design variations on one board: standalone pattern synthesis, and RS-485 controllable with a simple custom protocol.

I did the "architectural" design of both the hardware and software - describing the hardware design and writing the core software that runs everything.  Todd Polenberg did the hardware layout, handled the manufacturing, and wrote the pattern synthesis part of the software with my occasional consultation.  The hardware layout is a bit of a trick, while the board isn't particularly dense, the LEDs on one side of the board in a perfect circle and the electronics are as SMT as possible and are all on the backside.

The design is pretty simple: a TI TLC5940 16 channel PWM LED driver, and a PIC18F252 to run the show.  The PIC software is in C using the CCS C compiler.  The first design for Burningman was built with a 9V holder for wearing around.  The later revision for serial control has two 4-pin headers for daisy-chain for power/gnd/RS-485 and a standard 75176 8-pin SOIC RS-485 transceiver.  Picutred above is the prototype for the serial version, kludged to run off a 9V battery and with a pot to control brightness.

The TLC5940 is a very handly little chip, but not without some hassles.  See here for a discussion.

The RS-485 version hasn't been used much (at least not yet), but Leo has used a few in experimenting for installations.

These also make excellent "headlights" for bicycle riding at night in Oakland.  Of course, being Oakland, you can't leave it on your bike while you are at the bar...