Maybe this will help you:
The simplest low pass filter suitable for noisy signals is "floating average" (I don't know whether this is the correct name, but I call it like that)
If you have variable "x" you want to filter, then you can use this code:
last = 0;
function timer()
{
last = x0.1 + last0.9;
}
By calling the timer() function, the variable "last" slowly converges to the "x" value, the sum of weights (0.1+0.9) must be equal to 1. By changing the ratio you also change the "speed" of filter.
You can see a more intuitive example here:
http://www.valky.eu/?data/software/average.txt
FIR filters are complicated to design. If you want some specific filter with properly set cut off frequency and attenuation, you will need some filter designing tool (MATLAB has some toolboxes for this purpose). The IIR filters are not often used, because they are "crazy", by incorrect setting of the filter coefficients you can get some oscillating beast.
Gabriel