Schematic and Build
We have used the ATMega328 board. The LED is arranged in the current sink mode and four I/O pins of PORTB are used to connect to the LED with a series resistor of 100Ohm. The voltage on the LED is 3.5V so each pin will sink around 15mA. The maximum current through the LED is the 60mA.
We have made this project on a breadboard connected to the ATMega328 board. The board can be purched at www.bizztronix.eu.Get a piece of paper of about A6 size (10cm by 15cm), roll it into a cylinder, then glue the edges together so it remains that way. Then place the cylinder over the top of the LED. This will diffuse the light from the LED.
Five leads are connecting the pins from PORTB to the breadboard that contains also the four resistors and the LED.