If you want to cut the strip at any point, just be sure to leave connection points on each halve. Without getting too technical, its worth knowing that individual strips are made up of 3 LEDs in series which can be cut with clippers at any junction.
To accommodate a load that requires more current than 40mA at 5V, we will use our microcontroller to control a transistor, which will provide a component with power from an external source (the battery). To refer to the water analogy of electronics, the "pump pressure" is 5V, and the amount of water is the number of electrons (measured in Amps, or in our case, a much smaller amount - milliamps, mA). In other words, a component cannot draw more than 40mA of current from each channel. If you are new to Arduino and are wondering why more than a few LEDs or other components like motors won't activate when functions are called in the code, its because each output has a current limit of 40mA. Adafruit produces one variety called NeoPixels and they have an excellent guide. individually controllable LEDs), so I added an additional section for these as well (circuit and code). Update 2015: A lot of people seem to be interested in digitally-addressable LEDs (opposed to LEDs in "series", in other words the ones that blink together vs. You will need: - A Microcontroller - Breadboard or PCB - RGB LED strip - Battery (9-12v) - 3 NPN transistors (I'm using TIP 120s) - LM7805 Voltage regulator (optional, but recommended) - (4) 4-40 screws (length, up to you) - (4) 4-40 nuts - (4) nylon washers - 22g hookup wire
I will discuss how to mount a transistor to a heatsink & assemble the circuit but won't get into soldering as some RGB LED strips come with leads (and there is no shortage of great tutorials out there). This Instructable covers the assembly of a circuit capable of PWM-ing ( pulse width modulating) a 9-12v RGB LED strip and programming an Arduino to cycle through a range of colors.
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