The Adafruit Constant Current Boost Converter for LEDs makes driving LEDs easy, whether they're in series or parallel. This page will show you how to wire everything up. You'll need an LED, like this 12V nOOd, and a 3V to 5V power supply.

Wiring

Select Your Maximum Power Supply

The DIP switch on the breakout lets you select the current for your LED. The nOOd LED product page has a helpful listing of voltages and current draw. If you aren't sure on the maximum power supply for your LED, you can use this formula:

Iout = (Vin * 1.2A * 0.9 efficiency) / Vout

For this 12V nOOd with a 5V supply, the formula would be:

0.45 = (5 * 1.2A * 0.9 efficiency) / 12

Resulting in 0.45 amps aka 450 mA. The breakout has a limit of 425 mA on board (default 25 mA plus the current selection DIP switch), so 425 mA would be the maximum current you could use with this configuration, with all of the switches on the DIP switch set to "ON".

For another example, lets say you had a 3.3V supply and a 24V LED, like this nOOd. The formula becomes:

0.1485 = (3.3 * 1.2A * 0.9 efficiency) / 24

Resulting in 0.1485 amps aka 148.5 mA.

LEDs in Series

A common request, especially with fancy LED filaments like these letters, is to wire multiple LEDs together in series. This breakout is a great solution for this. You'll still use 3-5V as the input supply and connect your LEDs in series to the output terminal block. You'll set the current on the DIP switches for the maximum current for one LED.

When LEDs are wired in series, you add their voltages together. For the wiring diagram above, there are four LEDs and each needs 3V. This means you would need a total of 12V to power them (3V * 4 LEDs).

However, you don't use the formula from earlier to figure out the maximum current draw. You'll set the maximum current that is defined for one individual LED. In the case of the LED letter filaments, that's 100 mA maximum.