Using 1.5mm LEDs powered by USB

Hi,

you should connect LEDs to USB plug like on schematic:

You can add next LEDs (with resistors) similar to shown above.

As current which flows through LED must be limited, resistors are used. Values must be calculated according to type of LED and desired current. Most small LEDs have maximum current in 10-20 mA (milliamps, mA=0.001A) range. USB has output voltage 5V and LEDs have different forward voltages, you can assume 2V for red and amber ones, 3V for blue, white and true green (exact values can be found in datasheets).

To calculate resistor values, firstly LED current must be determined, for example 5mA. Then from Ohm's law:

R=U/I, where:

R - resistor value

U - voltage across resistor (so in our case USB voltage minus LED forward voltage)

I -LED current

For blue LEDs and 5mA current:

R=(5V-3V)/0.005A = 400 ohm

You can use standard value 390 ohm.

So you need: 15 pcs of LED lamp, 15 pcs of 390 ohm resistor and USB plug.

Total current should not exceed values showed above by Kelv.

You can use thin insulated copper wire, e.g. similar to:

http://uk.farnell.com/alpha-wire/6710-gr005/wire-eco-28awg-green-30-5m/dp/1764894

If current through single LED will be 5 mA, total current will be 15 * 5 mA = 75 mA, so below USB limit (100/500 mA) and USB will power all LEDs.