Wednesday, February 23, 2011
C.A.R.D.L.E Light Engine
A big part of the C.A.R.D.L.E desk lamps will be the actual lamps. Rather than using incandescent or halogen bulbs, they are full-color high-power LED light engines. I took the liberty of designing a custom driver board that can support 3 channels (red green and blue) which can be combined for any particular color. The actual driver chip is insanely small: it's a 3mm x 3mm package.
After considering a wide variety of possible driver chips, I chose the Maxim MAX16819 for a number of reasons including external PWM control and an external drive transistor, meaning it can handle arbitrarily high currents. (Only after a pretty exhaustive search did I find this great chart comparing LED drivers. Wish I had seen that earlier!) These are pretty beefy and can drive something like 30 watts depending on the LEDs chosen. I'm using these 10-watt multichip RGB LEDs from DealExtreme
Each channel is driven from the output of at ATTiny2313 configured for hardware PWM. The ATTiny listens for serial commands on the UART, and sets the PWM values for each output channel. Though I haven't needed to do it yet, there's an RS-485 receiver on the serial input so the board can programmed to understand DMX commands).