This is a basic RC low pass filter I modified the circuit to have an indicator LED on it, I used a 100 ohm resistor, although I probably should have gone with a 1K resistor or just left out the LED in general, as it is unnecessary.

I used a 330 nano-farad capacitor, but I think a larger value might work better, but then again, I'd have to experiment. (Or just do the math, but doing the math only shows you half of it)