Program to display heart rate and heart beat waveform based on photoplethysmography (PPG). It reads values from a sensor made of photodiode and LED and displays the corresponding heart rate and waveform on an LCD screen

1. #include <TFT.h> // Arduino LCD library
#include <SPI.h>
// SPI pin definition for the Mega. Check the SPI page on Arduino website for
more info
#define cs 10
#define dc 9
#define rst 8
#define sda 51
#define scl 52
TFT screen = TFT(cs, dc, rst);// create an instance of the screen library
unsigned long peaktArr[11], pAndt[2][3]; //peaktArr stores the peak values from
pAndt; pAndt stores the values from the sensor which are compared to one another
to determine a peak
float tdiff[10];//array to store time difference between consecutive time
stamps
int i = 0;
int j = 0;
int k = 0;
float inst_f = 0;
int p = 0;
int a = 0;
unsigned long calb;
int xPos = 0;//initial value (position) of the cursor that draws the waveform
void setup(){//the entire code in this loop will only happen 1 time
screen.begin();//initializing the screen
screen.setTextSize(2);//increasing text size 10X
screen.background(0, 0, 255);
unsigned long delayTime = millis();//millis() stores the amount of time in
milliseconds that has passed since it was introduced into the program. This
value is then passed into the variable delayTime
while(millis() - delayTime <= 3000){ // delayTime has a set value and will not
change and the program within the the while loop will run as long the difference
between millis() and delayTime is less than 3000 milliseconds or 3 seconds
screen.setCursor(0,0);///the 1st value in brackets sets the distance from the
left edge of the screen, and the 2nd value sets the distance from the top edge
of the screen
screen.print("Welcome To");
screen.setCursor(0,25);
screen.print("Chelsea's");
screen.setCursor(0,50);
screen.print("Heart Rate");
screen.setCursor(0,75);
screen.print("Device");
}
screen.background(0,0,255);//the 1st value is blue intensity, the 2nd is green
intensity and the 3rd is red intensity. this line makes the background color red
delayTime = millis();
while(millis() - delayTime <= 3000){
screen.setCursor(0,0);
screen.print("Place Finger");
screen.setCursor(0,25);
screen.print("On Sensor");
}
screen.background(0,0,255);
screen.setCursor(0,50);
screen.print("Calibrating");
for(i = 0; i < 3; i++){//read and store 3 values at a time in pAndt
unsigned long delayTime = millis();
pAndt[0][i] = analogRead(A0);//1st row of pAndt stores the sensor values
pAndt[1][i] = millis();// 2nd row of pAndt stores the time stamp of the
sensor values
while (millis() - delayTime <=200){//wait 200 ms before reading the next

2. sensor values. this means we read 5 values every second
}
}
for(i = 1; i < 2; i++){
if(pAndt[0][i]>pAndt[0][i-1] && pAndt[0][i]>pAndt[0][i+1]){ //compare the
3 values in pAndt to determine a peak
peaktArr[0] = pAndt[1][i];// store the value of i that satisfies the
peak condition
}
}
while(j<11){//the entire code within the while loop repeats until we get 11
values in peaktArr
//replace the values of the 1st column with those of the 2nd column
pAndt[0][0] = pAndt[0][1];//replace the values in row 1
pAndt[1][0] = pAndt[1][1];//replace the values in row 2
//replace the values of the 2nd column with those of the 3rd column
pAndt[0][1] = pAndt[0][2];//replace the values in row 1
pAndt[1][1] = pAndt[1][2];//replace the values in row 2
unsigned long delayTime = millis();//
for(i = 2; i < 3; i++){//read and store 1 value in the 3rd column of pAndt
pAndt[0][i] = analogRead(A0);//1st row of pAndt stores the sensor values
pAndt[1][i] = millis();// 2nd row of pAndt stores the time stamp of the
sensor values
while (millis() - delayTime <=200){//delay in ms before reading the next
value
}
}
for(i = 1; i < 2; i++){
if(pAndt[0][i]>pAndt[0][i-1] && pAndt[0][i]>pAndt[0][i+1]){ //compare the
3 values in pAndt to determine a peak
peaktArr[j++] = pAndt[1][i];// store the value of i that satisfies the
peak condition
}
}
}
for(i = 0; i < 10; i++){
tdiff[k++] = (((float)peaktArr[i+1] - (float)peaktArr[i])/1000);//change
the time values from unsigned long to float, take the difference between
consecutive time values, and convert the result to time in seconds
}
for(i = 0; i < 10; i++){
inst_f = inst_f + (1/tdiff[i]);//convert the time differences to
frequencies and take their sum
}
screen.background(0,0,255);
screen.setCursor(0,0);
screen.print("Heart rate ");
screen.setCursor(0,20);
screen.print((inst_f/10)*60);
screen.setCursor(75,20);
screen.println(" bpm");
while(xPos<=160){
int sensor = analogRead(A0);
int graphHeight = map(sensor,0,682,5,screen.height()/1.5);//map assigns
corresponding values between analog and digital. 0 is the lowest digital
reading,682 is the highest digital reading,5 is the position at which the lowest
reading will appear and screen.height()/1.5 is the position at which the highest
reading will appear

3. screen.stroke(255,255,255);
screen.line(xPos, (screen.height() - graphHeight), xPos, screen.height() -
graphHeight+3); //screen.height() - graphHeight + 5 affects the thickness of the
line. The bigger the number you add to screen.height() - graphHeight is, the
thicker the line will be
xPos++;
delayTime = millis();
while(millis() - delayTime<=25){//rate at which points are displayed on
screen to plot waveform
}
}
void loop(){
int xPos = 0;
float inst_f = 0;
for(i = 2; i<11; i++){
peaktArr[i-2] = peaktArr[i];//remove the 1st 2 values from the peaktArr array
and shift all the values until the last 2 "spots" in the array are empty
}
j = 9;//start filling peaktArr from index 9 (10th position)
for(i = 1; i<10; i++){
tdiff[i-1] = tdiff[i];//remove the earliest time difference that was
calculated and shift the other values until the last "spot" in the array is
empty
}
while(j<11){
pAndt[0][0] = pAndt[0][1];
pAndt[1][0] = pAndt[1][1];
pAndt[0][1] = pAndt[0][2];
pAndt[1][1] = pAndt[1][2];
unsigned long delayTime = millis();//
for(i = 2; i < 3; i++){
pAndt[0][i] = analogRead(A0);
pAndt[1][i] = millis();
while (millis() - delayTime <=200){
}
}
for(i = 1; i < 2; i++){
if(pAndt[0][i]>pAndt[0][i-1] && pAndt[0][i]>pAndt[0][i+1] /*&& pAndt[0][i]
>= 0.3*hp*/){ //compare the 3 values in pAndt to determine a peak
peaktArr[j++] = pAndt[1][i];// store the value of i that satisfies the
peak condition, and do the comparison above until j is 10
}
}
}
tdiff[9] = (((float)peaktArr[10] - (float)peaktArr[9])/1000);
for(i = 0; i < 10; i++){
inst_f = inst_f + (1/tdiff[i]);
}
screen.background(0,0,255);
screen.setCursor(0,0);
screen.print("Heart rate ");
screen.setCursor(0,20);
screen.print((inst_f/10)*60);
screen.setCursor(75,20);
screen.println(" bpm");
while(xPos<=160){
int sensor = analogRead(A0);
int graphHeight = map(sensor,0,682,5,screen.height()/1.5);
screen.stroke(255,255,255);

4. screen.line(xPos, (screen.height() - graphHeight), xPos, screen.height() -
graphHeight+3); //screen.height() - graphHeight + 5 affects the thickness of the
line. The bigger the number you add to screen.height() - graphHeight is, the
thicker the line will be
xPos++;
unsigned long delayTime = millis();
while(millis() - delayTime<=25){
}
}
screen.background(0,0,255);
screen.print("Calculating..");
unsigned long delayTime = millis();
while (millis()- delayTime <= 5000){
}
}