Program work when used Delay() but same program doesn't work with millis()

Question

I'm running a dc motor using esp32 and mosfet by taking readings of IR.

Program works fine when used delay() but same program doesn't work when uploaded using millis().

//This uses fixed delay()

// Pin definitions
const int irSensorPin = 34;  // IR sensor connected to GPIO 2
const int motorPin = 32;     // DC motor connected to GPIO 4

// Variables
bool isObjectDetected = false;

void setup() {
  // Initialize serial communication
  Serial.begin(9600);

  // Set pin modes
  pinMode(irSensorPin, INPUT);
  pinMode(motorPin, OUTPUT);
}

void loop() {
  // Check if object is detected
  if (digitalRead(irSensorPin) == LOW) {
    if (!isObjectDetected) {
      // Object detected for the first time
      isObjectDetected = true;
      Serial.println("Object detected. Stopping motor.");
      digitalWrite(motorPin, LOW);  // Stop the motor
      delay(500);                   // Wait for 500ms
      Serial.println("Resuming motor.");
      digitalWrite(motorPin, HIGH); // Start the motor
    }
  } else {
    if (isObjectDetected) {
      // Object is no longer detected
      isObjectDetected = false;
    }
  }
}

//This uses millis()

// Pin definitions
const int irSensorPin = 34;  // IR sensor connected to GPIO 34
const int motorPin = 32;     // DC motor connected to GPIO 32

// Variables
bool isObjectDetected = false;
unsigned long motorStopTime = 0;
const unsigned long motorDelayTime = 500;  // Delay time in milliseconds

void setup() {
  // Initialize serial communication
  Serial.begin(9600);

  // Set pin modes
  pinMode(irSensorPin, INPUT);
  pinMode(motorPin, OUTPUT);

  // Initialize motor state
  digitalWrite(motorPin, HIGH);  // Start the motor
}

void loop() {
  // Check if object is detected
  if (digitalRead(irSensorPin) == HIGH) {
    if (!isObjectDetected) {
      // Object detected for the first time
      isObjectDetected = true;
      Serial.println("Object detected. Stopping motor.");
      digitalWrite(motorPin, LOW);  // Stop the motor
      motorStopTime = millis();     // Record the stop time
    }
  } else {
    if (isObjectDetected) {
      // Object is no longer detected
      isObjectDetected = false;
      unsigned long currentTime = millis();
      if (currentTime - motorStopTime >= motorDelayTime) {
        Serial.println("Resuming motor.");
        digitalWrite(motorPin, HIGH); // Start the motor
      }
    }
  }
}

Answer 1

I am not sure I quite understand what the requirements are for this program. However, they do not do the same thing. I tried to represent their behavior as state diagrams, and here is what I got:

Version using delay():

Version using millis():

In the above diagrams, states with a gray background are those where the motor is off. As can be seen here, the first version never keeps the motor off for more than 0.5 s, where the second one can keep the motor indefinitely off if the sensor remains HIGH.

I suggest you start by drawing the state diagram corresponding to the behavior you actually want. Then, use the technique outlined in this tutorial on finite state machines to turn the diagram into code. Note that finite state machines work well with millis()-based timing.