LOWPASS(9)

NAME
lowpass - Low-pass filter

SYNOPSIS

loadrt lowpass [count=N|names=name1[,name2...]]

FUNCTIONS

lowpass.N (requires a floating-point thread)

PINS

lowpass.N.in float in

lowpass.N.out float out
    out += (in - out) * gain

lowpass.N.load bit in
    When TRUE, copy in to out instead of applying the filter equation.

PARAMETERS

lowpass.N.gain float rw

NOTES

gain pin setting

The digital filter implemented is equivalent to a unity-gain continuous-time single-pole low-pass filter that is preceded by a zero-order-hold and sampled at a fixed period. For a pole at -a (radians/seconds) the corresponding continuous-time lowpass filter LaPlace transfer function is:

H(s) = a/(s + a)

For a sampling period T (seconds), the gain for this HAL lowpass component is:

gain = 1 - e^(-a * T)

e = 2.71828 https://en.wikipedia.org/wiki/E_(mathematical_constant)

Examples: T = 0.001 seconds (typical servo thread period) a = (2 * pi * 100) (100Hz bandwidth single pole) gain = 0.466

       T = 0.001 seconds (typical servo thread period)
       a = (2 * pi * 10)     ( *10Hz* bandwidth single pole)
    gain = *0.0609*

       T = 0.001 seconds (typical servo thread period)
       a = (2 * pi * 1)      ( *1Hz* bandwidth single pole)
    gain = *0.0063*

AUTHOR

Jeff Epler

LICENSE

GPL