Here is described the easiest way to build a Wii sensor bar, it works for me with my dolphin emulator at 21 feets.
Only needed :
4 IR LEDS (Be sure a re Infra Red) $ 1.5
An unused USB cable (free)
SOme wire (about one feet) (Free)
Some plastic from an unused cassette box. (free)
A candle (found at any house)
A small bar or spare silicon (used in pistols)
Total: Around $. 2.-
OK. Be sure you peel the USB cable and will only use two cables, the red (+) and maybe a black or blue one (-)
On the IR Leds be sure to connect the longest feet (+) to red cable and make a serial circuit like the one shown in the pictures.
Once the circuit is complete, seal the connections with melted silicone, place the two sensors around 12" distance one to other.
Place all on the top of your LCD TV, connect the USB male to the USB connector on your TV.
You have now a WII remote sensor in less than 30 mins.