https://github.com/tttapa/filters

An Arduino finite impulse response and infinite impulse response filter library.
https://github.com/tttapa/filters

arduino arduino-library digital-filter dsp filter finite-impulse-response fir iir infinite-impulse-response

Last synced: 2 months ago
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An Arduino finite impulse response and infinite impulse response filter library.

• Host: GitHub
• URL: https://github.com/tttapa/filters
• Owner: tttapa
• License: gpl-3.0
• Created: 2017-12-30T21:01:01.000Z (about 7 years ago)
• Default Branch: master
• Last Pushed: 2019-11-14T01:26:37.000Z (about 5 years ago)
• Last Synced: 2024-03-16T11:42:25.556Z (10 months ago)
• Topics: arduino, arduino-library, digital-filter, dsp, filter, finite-impulse-response, fir, iir, infinite-impulse-response
• Language: C++
• Size: 2.12 MB
• Stars: 52
• Watchers: 8
• Forks: 10
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Filters

An Arduino finite impulse response and infinite impulse response filter library.

## New, Improved Arduino-Filters library

I created a new repository with an updated and improved version of this library.  

You can find it here: [**Arduino-Filters**](https://github.com/tttapa/Arduino-Filters).

## Digital filters

This library implements digital [finite impulse response](https://en.wikipedia.org/wiki/Finite_impulse_response) filters (FIR) 

and [infinite impulse response](https://en.wikipedia.org/wiki/Infinite_impulse_response) filters (IIR). 

Double precision floating point arithmetic is used.

### FIR

The difference equation for FIR filters is given by  

![FIR difference equation](https://wikimedia.org/api/rest_v1/media/math/render/svg/c43ba6c329a471401e87fe17c6130d801602ffdf)  

To initialize it in code, you can use:

```cpp

const double b_coefficients[] = { b_0, b_1, b_2, ... , b_N };

FIRFilter fir(b_coefficients);

```

### IIR

The difference equation for IIR filters is given by  

![IIR difference equation](https://wikimedia.org/api/rest_v1/media/math/render/svg/bddf0360f955643eeedc46d9be4b8f2d4f4d288f)  

```cpp

const double b_coefficients[] = { b_0, b_1, b_2, ... , b_P };

const double a_coefficients[] = { a_0, a_1, a_2, ... , a_Q };

IIRFilter iir(b_coefficients, a_coefficients);

```

### BiQuad Filters

When dealing with high-order IIR filters, they can get unstable.  

To prevent this, BiQuadratic filters (second order) are used.

Both Direct Form 1 and 2 are implemented.

```cpp

const double b_coefficients[] = { b_0, b_1, b_2 };

const double a_coefficients[] = { a_0, a_1, a_2 };

BiQuadFilterDF1 biquad1(b_coefficients, a_coefficients);

BiQuadFilterDF2 biquad2(b_coefficients, a_coefficients);

```

Optionally, you can specify a gain:

```cpp

const double b_coefficients[] = { b_0, b_1, b_2 };

const double a_coefficients[] = { a_0, a_1, a_2 };

const double gain = 1;

BiQuadFilterDF1 biquad1(b_coefficients, a_coefficients, gain);

BiQuadFilterDF2 biquad2(b_coefficients, a_coefficients, gain);

```

### Second Order Sections

Instead of manually cascading BiQuad filters, you can use a Second Order Sections filter (SOS).

```cpp

const double sosmatrix[][6] = {

    {b1_0, b1_1, b1_2,  a1_0, a1_1, a1_2 },

    {b2_0, b2_1, b2_2,  a2_0, a2_1, a2_2 }

};

const double gainarray[] = {1, 1};

SOSFilter<2> filter(sosmatrix, gainarray);

```

Here, `<2>` is the number of BiQuad filters in the SOS filter.

### Cascades of filters

You can apply multiple filters together in a cascade:

```cpp

Cascade cascade({&filter1, &filter2, ..., &filterN});

```

## Usage

The library provides a `Filter` interface with a `filter` method that takes the new (raw) value as an intput, and outputs the new (filtered) value.

```cpp

double raw_value = getRawValue();

double filtered_value = fir.filter(raw_value);

```

You can use multiple filters on the input.

```cpp

double filtered_value = fir.filter(iir.filter(raw_value));

```