Here's the latest project - motion-controlled glow fans for dancing with.
Inside each is a Picaxe 20X2, reading a 3-axis accelerometer, working out the hue from the angle of acceleration and the brightness from the total acceleration, chucking that info via I2C to a PCA9633 LED driver, which drives ten RGB LEDs via three transistors with 100 kHz PWM signals.
The video shows what they look like in motion, being tested at a dance party.
The big challenge for this one was making everything small enough that the electronics box could fit in a dancer's hand. The box is just a 3xAA battery box, with two AA's in there to power it. Hence the accelerometer board, 3 Watt power supply board, and Picaxe board had to fit in the space of one AA battery. It gets pretty warm. Without the new 20X2, this would not have been possible.
Getting them to look right also took a while. I'm faking a log response with dual-linear curves for both the hue and the brightness. There's also lots of filtering as the accelerometer data is fairly noisy and hysteresis on the response rates, fast when brightness goes up, slow when it goes down.