/ / Programmable LED
Making a Smart LED just means adding a microcontroller to an existing LED. Electrically, an RGB LED looks like three LEDs. An Atmel AVR ATtiny13 is the microcontroller brain. In this design the ATtiny13 is running at 4.8MHz from its internal oscillator with no clock scaling. That means it draws only about 1mA of current. The LEDs draw around 10mA for each color, so 30 mA total. But that’s a maximum, and by using PWM the average power consumption is a good deal less. If you know how to program an Arduino, you can program one of these chips. The result is soldered together directly without the need of a PCB. Its only input is two power pins. Hook these pins up to any voltage between 2.7V and 5.5V to light it up.
Adding senses to the Smart LED is easy. Add a piezo element as a knock sensor. Use a piezo as knock sensors is easy. By soldering the piezo directly to the Smart LED, a nice little package is made.If the piezo is struck, the LED turns white for a moment, then decaying down in brightness before returning back to the color changing. In this case, a common-cathode RGB LED with crystal-clear lens was used with a small diffuser on top.
RGB LEDs and Diffusers Most RGB LEDs you can find have a really narrow viewing angle, making them useful for flashlights maybe but not for ambient indicators. And because the red, green, and blue LED die are off axis from the integral lens that creates the narrow viewing angle, you don’t get very good color mixing. Sometimes you can find diffuse integral lenses on RGB LEDs but more often the lenses are crystal clear. By placing a small dab of diffusive material on top of the LED, the light is mixed and diffused. In this case, a cylinder of unmelted hot glue was used:
Source: todbot.com/blog/2007/03/25/smart-led-prototypes/