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ESP32-Based Password-Protected Relay Control with 4x4 Keypad

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Circuit Documentation

Summary

This circuit is designed to control a relay module using an ESP32 microcontroller and a 4x4 keypad. The user can enter an 8-digit password via the keypad, and if the password is correct, the relay will activate, unlocking a connected device. The circuit also includes two LEDs (orange and green) to indicate the status of the relay.

Component List

  1. ESP32-36PINS-DEVKIT-V1

    • Description: A development board based on the ESP32 microcontroller.
    • Pins: EN, IO36, IO39, IO34, IO35, IO32, IO33, IO25, IO26, IO27, IO14, IO12, IO13, IO09, IO10, IO11, GND, VIN, 3V3, IO06, IO07, IO08, IO00, IO15, IO02, IO04, IO16, IO17, IO05, IO18, IO19, IO21, IO03, IO01, IO22, IO23

  2. 4x4 Keypad

    • Description: A 4x4 matrix keypad used for user input.
    • Pins: C3, C2, C4, C1, R1, R2, R3, R4

  3. Relay module 5v-30v

    • Description: A relay module that can be triggered by a microcontroller to switch higher voltage loads.
    • Pins: common contact, normally open, normally closed, trigger, V-, V+

  4. LED: Two Pin (orange)

    • Description: An orange LED used to indicate the status of the relay.
    • Pins: cathode, anode

  5. LED: Two Pin (green)

    • Description: A green LED used to indicate the status of the relay.
    • Pins: cathode, anode

  6. Resistor (200 Ohms)

    • Description: A resistor with a resistance of 200 Ohms.
    • Pins: pin1, pin2

  7. GND

    • Description: Ground connection.

Wiring Details

ESP32-36PINS-DEVKIT-V1

4x4 Keypad

Relay module 5v-30v

LED: Two Pin (orange)

LED: Two Pin (green)

Resistor (200 Ohms)

Code Documentation

#define RELAY_PIN 17  // GPIO Pin connected to IN (trigger for relay)

// Define the password (8-digit password)
const char correctPassword[] = "12345678";  // Set your password here

// Variables for entering password
char enteredPassword[9];  // 8 digits + null terminator
int enteredIndex = 0;

// Pin mappings for the keypad (out1 - D32, out2 - D33, out3 - D25, out4 - D26, out5 - D27, out6 - D14, out7 - D12, out8 - D13)
const int keyPins[] = {32, 33, 25, 26, 27, 14, 12, 13};  // Declare the keyPins array

void setup() {
  Serial.begin(115200);

  // Initialize the relay pin
  pinMode(RELAY_PIN, OUTPUT);

  // Initialize the key pins
  for (int i = 0; i < 8; i++) {
    pinMode(keyPins[i], INPUT);
  }

  // Start with the relay off (NC is active by default)
  digitalWrite(RELAY_PIN, LOW);

  Serial.println("System initialized. Please enter the password.");
}

void loop() {
  // Read keys and detect which key is pressed
  for (int i = 0; i < 8; i++) {
    if (digitalRead(keyPins[i]) == HIGH) {  // Check if the key at the ith position is pressed
      char keyPressed = '1' + i;  // Map the pin index to the corresponding key (1-8)

      // Print the detected key
      Serial.print("Key pressed: ");
      Serial.println(keyPressed);

      // Store the pressed key
      if (enteredIndex < 8) {
        enteredPassword[enteredIndex] = keyPressed;
        enteredIndex++;
        enteredPassword[enteredIndex] = '\0';  // Null-terminate the string

        Serial.print("Entered: ");
        Serial.println(enteredPassword);
      }

      delay(200);  // Small delay to debounce keypress
    }
  }

  // If 8 digits are entered, check the password
  if (enteredIndex == 8) {
    if (checkPassword()) {
      Serial.println("Password is correct! Activating NO and unlocking...");

      // Unlock the lock (relay ON, NO is active)
      digitalWrite(RELAY_PIN, HIGH);

      delay(5000);  // Keep the lock open for 5 seconds

      // Turn off the relay after unlocking
      digitalWrite(RELAY_PIN, LOW);
      Serial.println("System relocked (no output).");
    } else {
      Serial.println("Incorrect password. NC remains active.");

      // Ensure relay stays in its default state (NC active)
      digitalWrite(RELAY_PIN, LOW);
    }

    // Reset the entered password for the next attempt
    resetPassword();
  }

  delay(100);  // Small delay to avoid flooding the serial monitor
}

// Function to check if entered password matches the correct password
bool checkPassword() {
  return (strcmp(enteredPassword, correctPassword) == 0);
}

// Reset the entered password
void resetPassword() {
  enteredIndex = 0;
  memset(enteredPassword, 0, sizeof(enteredPassword));
  Serial.println("Password reset. Please enter again.");
}

This code initializes the ESP32, sets up the relay and keypad pins, and continuously checks for key presses. When an 8-digit password is entered, it checks if the password is correct. If correct, it activates the relay to unlock a connected device for 5 seconds. If incorrect, it keeps the relay in its default state.