I have 10m unshielded cable going from an Arduino Uno to a simple Infrared led.
The led blinks when the signal goes out (I can verify this with camera) but the device what it should turn on does not turn on.
If I put another arduino (running the exact same code, IRemote library btw) to the IR led directly then it works.
So I know this sends PWM through the wire. Do I need to use shielded wire for this?
What's strange is that I have an IR receiver next to it, uses the same type of wire, same length and that works flawlessly.
What kind of IR led are you using? For a 10m cable, it might be a good idea to consider a higher power LED (100mA?) and use a transistor. I have a similar setup at home which works perfect.
Its common to use twisted pair for high current wiring, be it LEDs or motors or
supply - that way you can use thick enough wire to carry the current yet reduce
EMI substantially. Shielding is more useful for protecting weak signals from noise.
What current levels are being used? The cable will have 300pF capacitance or so,
probably, so unless the load is roughly similar to the characteristic impedance of the
cable you can expect waveform distortion on fast edges.