ESP32 - RFID with Relay

Video Tutorial

you can watch this video tutorial

Hardware Required

Introduction to RFID Module

Pinout

The RFID-RC522 module has 8 pins, some pins are shared among three communication interfaces: SPI, I2C, UART. At a time, only one communication mode can be used. The pin are:

• GND pin:connect this pin to GND (0V)
• VCC pin: connect this pin to VCC (3.3V)
• RST pin: is a pin for reset and power-down. When this pin goes low, hard power-down is enabled. On the rising edge, the module is reset.
• MISO/SCL/TX pin: works as:

  • - MISO pin if SPI interface is enabled
  • - SCL pin if I2C interface is enabled
  • - TX pin if UART interface is enabled.
• MOSI pin: works as MOSI if SPI interface is enabled.
• SCK pin:works as SCK if SPI interface is enabled
• SS/SDA/RX pin: works as:

  • SS pin if SPI interface is enabled
  • SDA pin when I2C interface is enabled
  • RX pin when UART interface is enabled.

Introduction to Relay

The relay is a programmable switch that can be used to control ON/OFF electrical devices. The relay can be programmatically controlled by ESP32 ⇒ ESP32 can control on/off the high voltage devices by using a relay.

Pinout

The relay pins can be categorized two groups: low voltage and high voltage.

The low voltage pins: are interfaced to ESP32, including three pins:

• GND pin:connect this pin to GND (0V)
• VCC pin: connect this pin to VCC (3.3V)
• IN pin: is a pin for reset and power-down. When this pin goes low, hard power-down is enabled. On the rising edge, the module is reset.

The high voltage pins: are interfaced to high-voltage device, including three pins (usually in screw

• NO pin: Normally Open pin
• NC pin:Normally Closed pin
• COM pin: the common pin

Normally, we do NOT use all high voltage pins. We usually use only two, depending on the operation mode we choose:

• Normally open mode: Use only COM pin and NO pin
• Normally closed mode:Use only COM pin and NC pin

How Relay Works

The relay has two operation modes:

• - Normally open mode
• - Normally closed mode.

Two modes works oppositely.

The “normally” means “if the IN pin is connected to LOW (0V)”.

Normally Open Mode

Connect the high-voltage device to the COM pin and NO pin. Just like a switch:

• If the IN pin is connected to LOW (0V), the switch is open. The device is OFF (or deactivated).
• If the IN pin is connected to HIGH (5V or 3.3V), the switch is closed. The device is ON (or activated).

Normally Closed Mode

Connect the the high-voltage device to the COM pin and NC pin. Just like a switch:

• If the IN pin is connected to LOW (0V) ⇒ The switch is closed ⇒ The device is ON (or activated).
• If the IN pin is connected to HIGH (5V or 3.3V) ⇒ The switch is open ⇒ The device is OFF (or deactivated).

Wiring Diagram

Breadboard Connections

Image is developed using Fritzing. Click to enlarge image

click to see ESP32 pin out

ESP32 Code

#include <SPI.h>
#include <MFRC522.h>
 
#define SS_PIN 5
#define RST_PIN 16
MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.

#define relayPin 4

void setup() 
{
  Serial.begin(9600);   // Initiate a serial communication
  SPI.begin();      // Initiate  SPI bus
  mfrc522.PCD_Init();   // Initiate MFRC522
  Serial.println("Approximate your card to the reader...");
  Serial.println();

  pinMode(relayPin,OUTPUT);

}
void loop() 
{
  // Look for new cards
  if ( ! mfrc522.PICC_IsNewCardPresent()) 
  {
    return;
  }
  // Select one of the cards
  if ( ! mfrc522.PICC_ReadCardSerial()) 
  {
    return;
  }
  //Show UID on serial monitor
  Serial.print("UID tag :");
  String content= "";
  byte letter;
  for (byte i = 0; i < mfrc522.uid.size; i++) 
  {
     Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
     Serial.print(mfrc522.uid.uidByte[i], HEX);
     content.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
     content.concat(String(mfrc522.uid.uidByte[i], HEX));
  }
  Serial.println();
  Serial.print("Message : ");
  content.toUpperCase();
  if (content.substring(1) == "D2 E4 DA 1B") //change here the UID of the card/cards that you want to give access
  {
    Serial.println("Authorized access");
    Serial.println();
    digitalWrite(relayPin,HIGH);
    delay(2000);
    digitalWrite(relayPin,LOW);
  }
 
 else   {
    Serial.println(" Access denied");
    delay(1000);
  }
}           

Book Tutorial

We are considering to make the book tutorials. If you think the book tutorials are essential, you can download it. download book

See Also

• ESP32 - Button - Debounce
• ESP32 - Button - Long Press Short Press
• ESP32 - Button Toggle LED

References

• Arduino IDE
• ESP32