emg.ino

//This code is used to recieve data from exg-pill and visualise it on serial plotter.

#define SAMPLE_RATE 500
#define BAUD_RATE 115200
#define INPUT_PIN A0


void setup() {
	// Serial connection begin
	Serial.begin(BAUD_RATE);
}

void loop() {
	// Calculate elapsed time
	static unsigned long past = 0;
	unsigned long present = micros();
	unsigned long interval = present - past;
	past = present;

	// Run timer
	static long timer = 0;
	timer -= interval;

	// Sample
	if(timer < 0){
		timer += 1000000 / SAMPLE_RATE;
		float sensor_value = analogRead(INPUT_PIN);
		float signal = EMGFilter(sensor_value);
    Serial.print(125);
    Serial.print(",");
    Serial.print(-125);
    Serial.print(",");
		Serial.println(signal);
	}
}

// Band-Pass Butterworth IIR digital filter, generated using filter_gen.py.
// Sampling rate: 500.0 Hz, frequency: [74.5, 149.5] Hz.
// Filter is order 4, implemented as second-order sections (biquads).
// Reference: 
// https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.butter.html
// https://courses.ideate.cmu.edu/16-223/f2020/Arduino/FilterDemos/filter_gen.py
float EMGFilter(float input)
{
  float output = input;
  {
    static float z1, z2; // filter section state
    float x = output - 0.05159732*z1 - 0.36347401*z2;
    output = 0.01856301*x + 0.03712602*z1 + 0.01856301*z2;
    z2 = z1;
    z1 = x;
  }
  {
    static float z1, z2; // filter section state
    float x = output - -0.53945795*z1 - 0.39764934*z2;
    output = 1.00000000*x + -2.00000000*z1 + 1.00000000*z2;
    z2 = z1;
    z1 = x;
  }
  {
    static float z1, z2; // filter section state
    float x = output - 0.47319594*z1 - 0.70744137*z2;
    output = 1.00000000*x + 2.00000000*z1 + 1.00000000*z2;
    z2 = z1;
    z1 = x;
  }
  {
    static float z1, z2; // filter section state
    float x = output - -1.00211112*z1 - 0.74520226*z2;
    output = 1.00000000*x + -2.00000000*z1 + 1.00000000*z2;
    z2 = z1;
    z1 = x;
  }
  return output;
}