Background: I am writing code that processes and identifies the QRS complex (R peak) in an ECG waveform for the 2nd lead.
Board Used: Arduino Uno Rev3
Issue: At the bottom of my code, I have a conditional that should print that the R peak was detected. I have confirmed that the code works as intended in the current version (what's posted below). When I remove the else statement, nothing prints anymore.
Attempts to Solve: I have stripped the code to try and identify where the issue is. When I have only the Serial.print("No"); in the else statement, the same issue occurs where nothing is detected apparently. Background research on other similar questions has not yielded much help.
** This code requires an input signal from a function generator using a 2.2Vpp 1Hz 0.6VDC offset ECG signal **
////// Library declarations
#include <stdio.h>
////// Input pin declarations
int lead2 = A0; // ECG
////// Variable declarations
float L2, L5;
float data_L2[5][5]; // by columns:
// time, input, filter, 1st derv, 2nd derv
float qrs[5][2]; // by columns:
// time, detected qrs input value
float trends[1000][2]; // by columns:
// time, rr_int
////// Data variables
// Data calculations
float tim, derv1, derv2, sum = 0;
// Flags
int flag1 = 0, flag2 = 0, flag3 = 0, flag4 = 0;
// ECG variables
float rr_int, qrs_time, qrs_data;
float gain;
// Internal detection flags
bool qrs_detect = false;
int tmp = 0;
///////////////////////////// SETUP /////////////////////////////////
void setup() {
// Beging serial monitor communication
Serial.begin(9600);
// Declaring pin modes for analog inputs
pinMode(lead2, INPUT);
}
///////////////////////////// LOOP //////////////////////////////////
void loop() {
// Reading input values
L2 = analogRead(lead2);
tim = millis(); // micros(); // use micros() if need greater precision. returns microseconds since startup
//
////// Smoothing input data //////
//
// Assigning data to arrays for time and input
for (int i = 4; i > -1; i--) {
if (i != 0) {
// Time data
data_L2[i][0] = data_L2[i - 1][0];
// Analog Values
data_L2[i][1] = data_L2[i - 1][1];
}
else {// if i=0
// Time data
data_L2[i][0] = tim;
// Analog values
data_L2[i][1] = L2;
}
}
//// ECG
// Smoothing data
sum = data_L2[1][1] + data_L2[0][1];
// Shifting data back
data_L2[4][2] = data_L2[3][2];
data_L2[3][2] = data_L2[2][2];
data_L2[2][2] = data_L2[1][2];
data_L2[1][2] = data_L2[0][2];
data_L2[0][2] = sum / 2;
//
////// First & Second Derivative
//
//// ECG Data
// Calculating first and second derivative
derv1 = data_L2[2][2] - data_L2[4][2]; // First Derv
derv2 = data_L2[2][2] - 2 * data_L2[3][2] + data_L2[4][2]; // Second Derv
// Shifting derivative values down
for (int i = 4; i > -1; i--) {
if (i != 0) {
data_L2[i][3] = data_L2[i - 1][3]; // first derv
data_L2[i][4] = data_L2[i - 1][4]; // second derv
}
else {
data_L2[i][3] = derv1; // first derv
data_L2[i][4] = derv2; // second derv
}
}
//
////// ECG Detection Scheme
//
// Looking at 5 values of derivatives
for (int i = 1; i < 4; i++) {
// First derv should be decreasing and have very large margins between previous and nex point (+/- 150)
if ((data_L2[i + 1][3] > 0) && (data_L2[i - 1][3] < 0)) { // Trying to find zero crossing
flag1++;
}
if(data_L2[i][4] < -300) {
flag2++;
}
// Checking flag for qrs detection
if (flag1 == 1 && data_L2[i][0] > qrs_time + 300 && flag2 == 1) {
// Saving time point for qrs
qrs_time = data_L2[i][0]; // saving time location
// Internal flag detection
qrs_detect = true;
// Breaks out of code so you don't have multiple detections on single QRS
break;
}
tmp = i;
}
// Resetting ECG flags
flag1 = 0;
flag2 = 0;
///////////////////////////
// Issue Area Below Pls Help
///////////////////////////
// Conditional that prints out data every new detection for ECG or BP
if (qrs_detect == true) {
// Setting internal ECG flag back to no detect
qrs_detect = false;
// Printing data
Serial.print("Detection");
Serial.print(",");
Serial.print(qrs_time/1000);
Serial.print(",");
Serial.println(tmp);
delay(1);
}
else {
Serial.print("No");
Serial.print(",");
Serial.println(data_L2[0][3]);
}
}
I'm not sure why I require this else statement and the Serial.print statements that are in it for my detection code to properly print out a positive detection. I also attached two images knowing that most people can't run this code to simulate my problem. The first image is of the Serial Monitor with the else statement included. At 12:04:50:459, a positive detection is recorded. The second image is where I removed
Serial.print(",");
Serial.println(data_L2[0][3]);
in the else statement. There should be a detection at the highlighted area, but there is not.
Please help 
Much thanks
