Assembly is simple and can be done by anyone. For this instructable I used Legos to house the wires and LEDs, but anything that will fit them will work.
Step 1: Supplies
4 infrared LEDs
1 USB cable
Electrical tape (optional)
wire stripper (optional)
something to house the LEDs and connections
and you will also need wire and a soldering iron OR 5 alligator clips.
If you use alligator clips it makes making the connections easier, but it will be harder to place it in a compact case.
Step 2: Open Up the USB Cable
Cut down the end of the plastic covering the wires about an inch down and cut off the rest of the plastic up to that point.
You should see 4 different colored wires. red, black, green, and white. Cut or pull back the green and white wires and tape them down. You don't need these wires since those are used to carry information.
Now strip the red and black wire about 1/3 of the way or so.
And insert the cord into your case.
Step 3: Making the Connections
If you are using alligator clips all you have to do is clip them on. Simple.
If you are new to soldering, make sure you have a damp sponge to keep the tip of the iron clean. Also be extremely careful not to touch any of the medal. I recommend soldering over cardboard that way if any solder touches it it won't stick easy. Just simply touch the wires together, put solder to it, and melt it with the soldering iron. The solder should stick to the wires. Also, try not to inhale the smoke.
Step 4: Applying the Tape
Step 5: Testing the Connections
Just plug it into any usb port while the device is on or that still provides power while in standby mode.
Use a camera or a phone or anything that takes pictures or video to make sure that the LEDS are lighting up (you can't see it with your own eyes).
Step 6: Choosing a Case
If you are not interested in making one out of Legos, simply skip to the last step.
Step 7: The Base of the Sensor Bar
Step 8: The Wall of the Sensor Bar
Step 9: Placing in the Components
Make sure the LEDs are close enough to each other and far enough apart.
Step 10: The Flaps
Step 11: The Finished Case.
The spots above the LEDs were filled with the flaps made in the last step.