You will need:
Scissors or wire cutters (available for use at TechShop)
Wire strippers (available for use at TechShop)
Soldering Iron (available for use at TechShop)
"Helping hands" or clamps (available for use at TechShop)
Any length of LED strip
LED strips have two common features which are important to this Instructable. First, LED strips are divided into segments. The strips can be cut at any length provided the cut is on the line usually indicated by a small scissors icon. LED strips that are severed or cut between these lines will not function to the fullest. Second, LED strips have a positive (+) and a negative (-) soldering hard point that is on the strip. The convention does matter, since they run from DC power. There are a pair of these points at the beginning and the end of each segment.
Step 1: [photo1]
Cut the LED strip along an indicated line to give you a length close to the desired length. If you cut too long, you can always cut again, too short and you may have to do more soldering.
Remove the waterproofing or plastic covering, if applicable, so that the soldering hard points are free.
Pre-tin the hard points. Some LED strips have this step finished for you already! Pre-tinning refers to the procedure by which you solder a small blob of solder onto the object in question. In order for this to work the best, you must heat up the element so that the solder wicks onto it...not just lays on top and cools. This works best with a conical soldering tip and a small amount of solder for thermal conductivity. Once the desired temperature is reached, you will see the solder wick onto the surface. Add more in necessary. You should have enough to cover the hard point, but not be at risk of melting through the strip or reaching the other hard point, causing a short.
Cut and strip the wire a desired length. Again, cut longer than you think you will need. Strip only a small length of wire, like 1/8" or less. If the wire is stranded, twist the strands together to keep them from separating. The best wire will be thin enough to move around tightly, I prefer 22-24 AWG solid core.
A quick word about current. LED strips sink current and depending on the length increase the amperage of current in the circuit. Wires can extend the reach of your LED strips and do not count towards the drawn current (measured in amperes, A or milliamperes, mA). Please refer to the manufacturer's documentation for the specifics. Most segments take somewhere between 20 and 100 mA. For example, my five foot section from the hardware store totals 250mA...which is 1/4 of the total my DC adapter puts out, which is 1A or 1000mA.
Step 5: [photo 2, 3]
Pre-tin the end of the wire.
Using helping hands or a vice, mount the wire and the strip so that it takes minimal or no effort to get the wire and the hard point to touch.
Step 7: [photo 4]
Quickly touch the soldering iron to the wire and the hard point at the same time. If we pre-tinned our connections, they should quickly form a solid contact. Remove from heat.
Best of luck,
~Zack @ TechShop San Francisco