Help With Arduino Code!

Firmware
1

I’m currently trying to figure out how to use millis to measure the time between each blink of an LED (the blink being caused by a pulse sensor plugged into an analog input) and take this information to trigger a digital pin if the interval between blinks is greater than 500.

Here’s my current code:

int PulseSensorPurplePin = 0; 
int ledPin = 13;
int SHOCK =  9;

int Signal;
int Threshold = 550;
unsigned long previousMillis = 0;
unsigned long startMillis;
const unsigned long interval = 500;

void setup() {
 pinMode(SHOCK,OUTPUT);
 pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
  
}

void loop() {

 Signal = analogRead(PulseSensorPurplePin); 
 unsigned long currentMillis = millis();
  Serial.println(Signal);

  
  if(Signal > Threshold){  
    digitalWrite(ledPin,HIGH);       
  } else {
    digitalWrite(ledPin,LOW);  
  }

  if(currentMillis - previousMillis > interval){       
    digitalWrite(SHOCK,HIGH);       
  } else {
    digitalWrite(SHOCK,LOW);
  } 
delay(10);
 }
3

I think you need to define your analog pin, maybe A0? Then under setup:

pinMode(PulseSensorPurplePin, INPUT)

I’m not versed in arduino code, but this makes sense to me.