org.usfirst.frc.team1736.lib.SignalMath

Class FIRFilter

java.lang.Object

org.usfirst.frc.team1736.lib.SignalMath.FIRFilter

public class FIRFilter
extends java.lang.Object

Generic Finite Impluse Response (FIR) filter. Constructor takes an argument to indicate what sort of filter to implement. Underlying logic remains the same for all filters, but coefficent value and number change to implement different cutoff frequencies and styles.

A FIR filter is effectively a weighted average of past signal values, but with specifically chosen weights to allow or disallow specific frequencies through. Lowpass filters allow low frequencies but block high frequencies, while Highpass filters allow higher frequencies but block lower ones. The number indicates the aproximate frequency at which the filter transitions between blocking and not blocking.

FIR filters must process samples at a very regular rate to maintain accuracy. For this reason, this implementation outsources the computation of filter value to a separate task, called at a 20ms rate (50Hz). This limits the max. frequency that can be processed by the filter to 25Hz (per the Nyquist Criteria).

Field Summary

Fields

Modifier and Type	Field and Description
FilterType	type Type of filtering this filter is doing.

Constructor Summary

Constructors

Constructor and Description
FIRFilter(FilterType type_in) Initalize memory for the filter, and start periodic calculations in the background.

Method Summary

Modifier and Type	Method and Description
double	getFilterOutput() Get the present output of the filter.
void	setInput(double val) Set a new input into the filter.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

type

public final FilterType type

Type of filtering this filter is doing. If for some reason you forgot what type it was, check it here

Constructor Detail

FIRFilter

public FIRFilter(FilterType type_in)

Initalize memory for the filter, and start periodic calculations in the background.

Parameters:

type_in - Type of filter to execute

Method Detail

setInput

public void setInput(double val)

Set a new input into the filter. Whatever is passed here will be picked up next time the filter task calculates the filter's value.

Parameters:

val - Input to the filter

getFilterOutput

public double getFilterOutput()

Get the present output of the filter.

Returns:

Filter's present output value