duecce / Arduino_RealTime_FIR

Use this library to compute Finite Impulse Response filter.

Arduino Real-Time FIR

This library computes Finite Impulse Response Filter.
Filter coefficients, for example, could be evaluate in Matlab (R) and then passed as arguments in the FIR constructor method.

Usage example

Arduino_RealTime_FIR is a library composed by one class: RT_FIR.
RT_FIR class has a constructor and 3 methods. Uses of this library is very simple:

1. create an instance of RT_FIR object defining filter coefficients
2. filter each sample of your signal

How to make a RT_FIR instance

To make a RT_FIR instance you need to declare a RT_FIR object and then pass the filter parameters to the constructor method:

...
RT_FIR <T> fir = new RT_FIR(nb, b);
...

Where: b is an array (of type:T, eg: T = double or float) contains numerator coeffs, nb is the length of b array.
RT_IIR is a template class, so you are allow to filter float or double (or other type) typed samples.

How to filter samples

To filter new sample acquired you have to call fir.add(T sample) method as follows:

...
filteredSample = fir.add(sample);
...

fir.add(T sample) add a new sample to the list of samples in processing and computes the filtering operation. This method return the result of the filtering operation.
fir.compute() return the result of filtering operation without any new sample added to the filtering samples queue.
fir.getLastOutput() return the value of the last result obtained by fir.add(T sample) or fir.compute() method.

Application example: moving average filter applied to AD8232 output using Arduino

This example uses RealTime_FIR library to filter the signal acquired from an AD8232 connected to an Arduino Uno (Single-Lead, heart rate monitor front-end): AD8232 datasheet

#include "RealTime_FIR.hpp"

// To implement a more complex FIR filter you can get the FIR coefficients using Matlab or http://t-filter.engineerjs.com/
// or in many other way

float FIRcoeff[] = {0.25, 0.25, 0.25, 0.25}; // Simple coefficients for a moving average with n=4
RT_FIR<float> fir = RT_FIR<float>(4, FIRcoeff); // RT_FIR instance

void setup() {
  // initialize the serial communication:
  Serial.begin(9600);
  pinMode(10, INPUT); // Setup for leads off detection LO +
  pinMode(11, INPUT); // Setup for leads off detection LO -
}

// to correct filtering data you have to know the real adc sample frequency, in this example I didn't implement it
// It can be done using a timer
void loop() {
  float input;
  if((digitalRead(10) == 1)||(digitalRead(11) == 1)){
    Serial.println('!');
  }
  else{
    input = (float) analogRead(0);
    Serial.println(fir.add(input));
  }
  delay(1);
}