How to use an IR led that has been mounted to a PCB

I think what they're doing with the kit is making it so that every module has 3 wires, in the same places. The idea is that you can just do the same thing and then replace the module without worrying about re-wiring.

For the LED, think of it like this:

• A5 has got a 38kHz square wave on it, between 0 and 3.3v
  
• A6 turns on only when you want the light to come out of the LED
  
• The LED is connected between A5 and A6, so the voltage across it is A6-A5.
  
• The LED itself will only conduct (and light up) when there's a positive voltage across it. A negative voltage won't hurt, but it won't make it light up.
  
  

So if you look at the graphs below (time is left->right, voltage is up->down), at the bottom there's A6-A5. When A6 is 0, the voltage goes between 0 and -3.3v (so no light), but when A6 is 3.3v, the voltage is now between 0 and 3.3v, so when the square wave goes high, the LED lights up (shown by the shaded part of the square wave).

(So the signal out of it isn't really weaker, it's just only on half the time)

Does that help?

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