Cascading Low Pass Filter Parameters
Here's what I use when I want to implement a software low pass filter. The picture shows how to derive it. All you've got to do is plug in the numbers representative of the C and R values and the sample time period: -



The digital filter I've shown is of the form: -

OUT(n) = OUT(n-1) * (1 - T/CR) + IN(n-1) * (-T/CR)  

If you want a more rigorous proof read this. It's called digital filter design for analogue engineers.