ESP32 Smart Door Lock

BuildWhat You Will Build

GoalsLearning Objectives

• Wire and test the MFRC522 RFID reader before connecting the rest of the circuit.
• Map each signal to a named ESP32 GPIO and keep the code constants readable.
• Control the servo signal on GPIO26 using an explicit approved-card decision.
• Use Serial Monitor as an engineering tool, not only as a success message.
• Identify power, wiring, and timing faults using a repeatable test checklist.

PartsComponents List

• PartESP32 DevKit boardMain controller
• PartMFRC522 RFID readerCard reader used for the access decision
• PartSmall hobby servo or low-voltage lock actuatorDemonstration lock movement controlled from GPIO26
• PartBreadboard and jumper wiresPrototype wiring
• PartUSB data cableProgramming and testing

PartsBill of Materials

🔗Wiring

Wire the MFRC522 RFID reader first, verify card reads in Serial Monitor, then connect the servo signal on GPIO26. Keep the build low-voltage and treat the servo or lock mechanism as a classroom prototype.

1. 1

   Unplug USB before placing modules on the breadboard.

2. 2

   Connect the MFRC522 RFID reader power pins according to its module label; common MFRC522 boards use 3.3 V logic, not 5 V GPIO signals.

3. 3

   Connect MFRC522 SS/SDA to GPIO5 and RST to GPIO22 to match the code constants.

4. 4

   Connect the MFRC522 SPI bus to the ESP32 SPI pins used by your board and library setup.

5. 5

   Connect the servo signal wire to GPIO26 and share ground with the ESP32.

6. 6

   Power the servo or lock actuator from a suitable low-voltage supply if USB power is not stable; do not power a motorized lock directly from an ESP32 GPIO.

7. 7

   Upload the sketch, scan a known card, and verify Serial Monitor before attaching the lock mechanism.

GPIO Mapping

Circuit Explanation

Engineering Explanation

⌨️Code

Copy into Arduino IDE. Install any libraries noted in the component guides first.

#include <SPI.h>
#include <MFRC522.h>
#include <ESP32Servo.h>

#define SS_PIN 5
#define RST_PIN 22
#define SERVO_PIN 26

MFRC522 rfid(SS_PIN, RST_PIN);
Servo lockServo;
byte allowedUid[] = {0xDE, 0xAD, 0xBE, 0xEF};

bool allowedCard() {
  if (rfid.uid.size != sizeof(allowedUid)) return false;
  for (byte i = 0; i < rfid.uid.size; i++) {
    if (rfid.uid.uidByte[i] != allowedUid[i]) return false;
  }
  return true;
}

void setup() {
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  lockServo.attach(SERVO_PIN);
  lockServo.write(0);
  Serial.println("Door lock ready");
}

void loop() {
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;
  if (allowedCard()) {
    Serial.println("Unlocked for 5 seconds");
    lockServo.write(90);
    delay(5000);
    lockServo.write(0);
  } else {
    Serial.println("Unknown card");
  }
  rfid.PICC_HaltA();
}

Code Explanation