(images (c) Kate Raudenbush)
I’ve been spending the last month on-and-off working on this exciting sculpture from ultra-talented Kate Raudenbush, who designed and is fabricating the main part of the 90′ sculpture. It is made of 240 ‘wings’ of 4′ x 8″ plasma-cut steel sheet and mirrored red acrylic. At the tip of each wing is a red LED.

Kate came to me with these drawings and her original plan: the red LEDs would form a ‘4-chase’ sequence. The budget is around $500 for all electronic parts, including LEDs, wiring, power, batteries, tools, etc. I decided to push the project a little futher: instead of a simple chase (which was well within reason), we would have each LED be individually controlled and PWM’d so that complex designs could be realized.
The biggest constraint (apart from the budget) is that all the electronics must fit in the square wing-support tube: .8″x.8″ and any wiring and connectors have to fit through a .5″ hole that was already drilled in the wings.

As always, I specified the connector first. Because of the small space, I couldn’t go with a feed-thru connector, and originally I wanted to use phone/cat5 cable and connectors but they wouldnt fit either. So in the end I was forced to go with 4-pin 0.1″ Molex MTA. It’s not the best but it’s dirt cheap and I’ve worked with it before. The connector pins pass power (3-5V), ground, data receive & clock. I decided against i2c and stuck with SPI because I’ve had good luck with it. It’s also more reliable than serial because of the clock.

To control the LEDs I picked the ATtiny13, which ends up being 75 cents each at the quantities I’m dealing with. It’s an 8 pin device: 2 pins for power, one for reset, and three for LEDs. The PWM code is written in C and uploaded to the chip using a surface-mount IC clip.