FilterLib is a collection of digital filters (highpass, lowpass, etc.) written in C. The aim is to provide quick and easy implementations of common filters, without needing to rewrite the same code over and over again. Specific filter types can be incorporated in code using a single include statement and filter parameters (such as cut-off frequency and sampling frequency) are easily set using the class constructor.
Source files (.cpp and .h) are located in the src folder. An example implementation for Arduino is located in the examples folder.
#include "ButterworthLPF.h"
#define PI 3.14159265359
// Sample time of simulation (in microseconds)
#define SAMPLE_TIME_US 10000
// Set filter parameters
#define LPF_ORDER 1
#define LPF_CUTOFF_FREQ 10
#define LPF_SAMPLE_FREQ 100
// Create low-pass filter object
ButterworthLPF lpf(LPF_ORDER, LPF_CUTOFF_FREQ, LPF_SAMPLE_FREQ);
// Simulated signal parameters
#define BASE_FREQ 5.0
#define NOISE_PWR 0.000001
float dt;
unsigned long counter;
unsigned long timer;
void setup() {
// Initialise serial port
Serial.begin(115200);
while (!Serial);
// Calculate sample time in seconds
dt = (float) SAMPLE_TIME_US / 1000000.0;
// Reset counter
counter = 0;
// Initialise timer
timer = micros();
}
void loop() {
if (micros() - timer >= SAMPLE_TIME_US) {
// Generate next sample of sinusoid with additive random noise
float measurement = sin(2 * PI * BASE_FREQ * dt * counter) + NOISE_PWR * random(-1000, 1000);
// Filter measurement
float filtered = lpf.update(measurement);
// Print measurement and filtered value
Serial.print(measurement); Serial.print(","); Serial.println(filtered);
counter++;
timer += SAMPLE_TIME_US;
}
}Contributions to additional filter types and classes are very welcome.