The design of the 2x2 LED cube is fairly simple as each layer only consists of 4 LEDs.
Each LED has a positive terminal (anode) and a negative terminal (cathode). There are two methods to determine the LED's terminal.
|Figure 1. Largest piece among the 2 conductors is the cathode.||6|
From the figure,
1. Anode is +, cathode is -
2. Observe flat surface at cathode compared to anode.
SuperBright Blue LED wavelength: 470nm
Forward voltage: 3.4v
Max forward current: 30mA
View angle: 0 to ~15 degrees.
Intensity : 4000mcd (max)
Resistance: 100 ohm , 1/8 watt (0.25 watt)
Theoretical max forward current : (5v output - 3.4) / 100 = 16mA
Actual current draw: 8.5mA (max due to pulse)
Actual voltage output: 4.8v
Actual voltage across LED: ~3.4v
Actual power dissipated by resistor = (8.5m)^2 * 100 = 0.007A