This LED "icicle" made from mainly blue LEDs. This device can serve as Christmas present or New Year's ornament. The "icicle" can be transformed into a "candle" if to use red and yellow LEDs and to change accordingly its external design. As the body I used two fur-tree toys: transparent plastic icicle and one-half of the Christmas ball. LEDs are placed in the first and second placed the microcontroller board.
The circuit of the device is shown in the figure below. 26 LEDs are connected to the pins of the microcontroller IC2 ATMega8515. 8 of them are connected directly, and 18 - through the transistor switches. I used different colored LEDs: 2 red, 2 green, 2 yellow, 2 white and 18 blue. All LEDs are connected via 300 Ohm resistors. Between bases of transistors and microcontroller used 4.7K resistors, and between bases of transistors and "ground" - 1K resistors.
The PCB looks as follows (I initially forgot to put in the circuit resistors between bases of transistors and the ground which then had to install over the top):
The assembled icicle looks as follows:
Control program for the microcontroller works as follows: when you turn on the device the brightness of all leds is set to a pseudo-random value. Then, the leds start to gradually change their brightness at different speeds. Then periodically flicker rate of different leds are changing randomly. As result, the icicle will be iridescent. The rate of blinking can be changed in the firmware sources.
On the links below you can download the circuit and PCB (for Eagle) and the firmware with sources.
Then you can watch a video of the device.