DiscreteFilter

Arduino library for implementing discrete-time filters. This library allows for the implementation of time-invariant filters of arbitrary order with constant-coefficient discrete-time transfer functions. Functions for quickly creating common filters(low-pass, high-pass filters) are included.

This library is still very much a work in progress. Be aware that code-breaking updates may be unavoidable as features are added.

Documentation

Coming Soon.

Examples

An examples folder is under development.

For the moment, here is an example of how the library can be used:

// Declare empty filter objects
DiscreteFilter lpfilter;  // Low-pass filter
DiscreteFilter hpfilter;  // High-pass filter

// Create complementary low- and high-pass filters
lpfilter.createFirstOrderLowPassFilter(FILTER_DT,FILTER_TAU);
hpfilter.createFirstOrderHighPassFilter(FILTER_DT,FILTER_TAU);

// Move the filters forward by one time step
// (should be performed once every FILTER_DT seconds)
float lowpassoutput = lpfilter.step(input);

// The most recent output can also be accessed with the "getLastOutput()" function
hpfilter.step(input);
float highpassoutput = hpfilter.getLastOutput();

// Custom filters/controllers can also be implemented
// (this example is identical to "createFirstOrderLowPassFilter()"
//  except that it includes filter saturation)
int   order = 1;                // 1st order filter
float saturation = 100.0;       // Don't output anything beyond +/- 100

float filterconst   = FILTER_DT/FILTER_TAU;
float numerator[]   = {filterconst, 0};
float denominator[] = {1, filterconst-1};
DiscreteFilter customlowpass(order, numerator, denominator, saturation);

// Sasturation can be added to any filter:
lpfilter.setSaturation(100.0);

// Now lpfilter and customlowpass are functionally identical

// Saturation can be disabled by setting it to 0 or a negative value
hpfilter.setSaturation(0);

// The filter inputs/outputs can be cleared:
lpfilter.clear();
hpfilter.clear();

// Various self-explanatory setters and getters exist:
hpfilter.setOrder(1);
hpfilter.setGain(1.0);
hpfilter.setNumerator(numerator);
hpfilter.setDenominator(denominator);

float input0  = hpfilter.getInput(0);
float output0 = hpfilter.getOutput(0);
float hpgain  = hpfilter.getGain();
int   hporder = hpfilter.getOrder();

Installation

To install, download this library as a .zip or .tar.gz from github and place the extracted folder in your sketchbook's "libraries" folder