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.TH LOWPASS "9" "2023-02-10" "LinuxCNC Documentation" "HAL Component"
.SH NAME

lowpass \- Low-pass filter
.SH SYNOPSIS
.HP
.B loadrt lowpass [count=\fIN\fB|names=\fIname1\fB[,\fIname2...\fB]]
.SH FUNCTIONS
.TP
\fBlowpass.\fIN\fB\fR (requires a floating-point thread)

.SH PINS
.TP
.B lowpass.\fIN\fB.in\fR float in \fR
.br
.ns
.TP
.B lowpass.\fIN\fB.out\fR float out \fR
 out += (in - out) * gain 
.TP
.B lowpass.\fIN\fB.load\fR bit in \fR
When TRUE, copy \fBin\fR to \fBout\fR instead of applying the filter equation.
.SH PARAMETERS
.TP
.B lowpass.\fIN\fB.gain\fR float rw \fR
.SH NOTES



\fBgain\fR 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 \fB-a\fR (radians/seconds) the corresponding continuous-time
lowpass filter LaPlace transfer function is:

\fBH(s) = a/(s + a)\fR

For a sampling period \fBT\fR (seconds), the gain for this
Hal lowpass component is:

\fBgain = 1 - e^(-a * T)\fR

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

\fBExamples:\fR
     T = 0.001 seconds (typical servo thread period)
     a = (2*pi*100)    (\fB100Hz\fR bandwidth single pole)
  gain = \fB0.466\fR

     T = 0.001 seconds (typical servo thread period)
     a = (2*pi*10)     ( \fB10Hz\fR bandwidth single pole)
  gain = \fB0.0609\fR

     T = 0.001 seconds (typical servo thread period)
     a = (2*pi*1)      ( \fB1Hz\fR bandwidth single pole)
  gain = \fB0.0063\fR

.SH AUTHOR

Jeff Epler
.SH LICENSE

GPL