Arduino - RFID/NFC - Relay
In this tutorial, we are going to learn how to use RFID/NFC tag to activate relay using Arduino. You can extend this tutorial by using the relay to control motor, actuator...
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If you do not know about RFID/NFC RC522 Module and relay (pinout, how it works, how to program ...), learn about them in the following tutorials:
The UIDs of some RFID/NFC tags are preset in Arduino code
User taps an RFID/NFC tag on RFID/NFC reader
The reader reads UID from the tag.
Arduino gets the UID from the reader
Arduino compares the read UID with the predefined UIDs
If the UID is matched with one of the predefined UIDs, Arduino activates the relay.
This image is created using Fritzing. Click to enlarge image
To simplify the setup, the pins of the RC522 module are directly connected to the pins of the Arduino. However, this can cause the Arduino to stop working in certain situations, as the output pins of the Arduino supply 5V while the RC522 module's pins are designed to function at 3.3V. It is therefore advisable to regulate the voltage between the Arduino pins and the RC522 module's pins. For additional information, please refer to the Arduino - RFID RC522 tutorial. The following diagram illustrates how to use resistors to regulate 5V to 3.3V:
This image is created using Fritzing. Click to enlarge image
※ NOTE THAT:
The order of pins can vary according to manufacturers. ALWAYS use the labels printed on the module. The above image shows the pinout of the modules from DIYables manufacturer.
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 10
#define RST_PIN 5
#define RELAY_PIN A5
MFRC522 rfid(SS_PIN, RST_PIN);
byte authorizedUID[4] = {0xFF, 0xFF, 0xFF, 0xFF};
void setup() {
Serial.begin(9600);
SPI.begin();
rfid.PCD_Init();
pinMode(RELAY_PIN, OUTPUT);
digitalWrite(RELAY_PIN, LOW);
Serial.println("Tap RFID/NFC Tag on reader");
}
void loop() {
if (rfid.PICC_IsNewCardPresent()) {
if (rfid.PICC_ReadCardSerial()) {
MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
if (rfid.uid.uidByte[0] == authorizedUID[0] &&
rfid.uid.uidByte[1] == authorizedUID[1] &&
rfid.uid.uidByte[2] == authorizedUID[2] &&
rfid.uid.uidByte[3] == authorizedUID[3] ) {
Serial.println("Authorized Tag");
digitalWrite(RELAY_PIN, HIGH);
delay(2000);
digitalWrite(RELAY_PIN, LOW);
}
else
{
Serial.print("Unauthorized Tag with UID:");
for (int i = 0; i < rfid.uid.size; i++) {
Serial.print(rfid.uid.uidByte[i] < 0x10 ? " 0" : " ");
Serial.print(rfid.uid.uidByte[i], HEX);
}
Serial.println();
}
rfid.PICC_HaltA();
rfid.PCD_StopCrypto1();
}
}
}
Because UID is usually not printed on RFID/NFC tag, The first step we need to do is to find out the tag's UID. This can be done by:
Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to Arduino
Open Serial Monitor
Tap an RFID/NFC tag on RFID-RC522 module
Get UID on Serial Monitor
Tap RFID/NFC tag on reader
Unauthorized Tag with UID: 3A C9 6A CB
After having UID:
Update UID in the line 18 of the above code. For example, change byte authorizedUID[4] = {0xFF, 0xFF, 0xFF, 0xFF}; TO byte authorizedUID[4] = {0x3A, 0xC9, 0x6A, 0xCB};
Upload the code to Arduino again
Tap an RFID/NFC tag on RFID-RC522 module
See output on Serial Monitor
Tap RFID/NFC tag on reader
Authorized Tag
Tap RFID/NFC tag on reader
Authorized Tag
Unauthorized Tag with UID: BD 1E 1D 00
We can allow multiple RFID/NFC tags to activate the relay. The below code uses two tags as an example.
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 10
#define RST_PIN 5
#define RELAY_PIN A5
MFRC522 rfid(SS_PIN, RST_PIN);
byte authorizedUID1[4] = {0x3A, 0xC9, 0x6A, 0xCB};
byte authorizedUID2[4] = {0x30, 0x01, 0x8B, 0x15};
void setup() {
Serial.begin(9600);
SPI.begin();
rfid.PCD_Init();
pinMode(RELAY_PIN, OUTPUT);
digitalWrite(RELAY_PIN, LOW);
Serial.println("Tap RFID/NFC Tag on reader");
}
void loop() {
if (rfid.PICC_IsNewCardPresent()) {
if (rfid.PICC_ReadCardSerial()) {
MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
if (rfid.uid.uidByte[0] == authorizedUID1[0] &&
rfid.uid.uidByte[1] == authorizedUID1[1] &&
rfid.uid.uidByte[2] == authorizedUID1[2] &&
rfid.uid.uidByte[3] == authorizedUID1[3] ) {
Serial.println("Authorized Tag 1");
digitalWrite(RELAY_PIN, HIGH);
delay(2000);
digitalWrite(RELAY_PIN, LOW);
}
else
if (rfid.uid.uidByte[0] == authorizedUID2[0] &&
rfid.uid.uidByte[1] == authorizedUID2[1] &&
rfid.uid.uidByte[2] == authorizedUID2[2] &&
rfid.uid.uidByte[3] == authorizedUID2[3] ) {
Serial.println("Authorized Tag 2");
digitalWrite(RELAY_PIN, HIGH);
delay(2000);
digitalWrite(RELAY_PIN, LOW);
}
else
{
Serial.print("Unauthorized Tag with UID:");
for (int i = 0; i < rfid.uid.size; i++) {
Serial.print(rfid.uid.uidByte[i] < 0x10 ? " 0" : " ");
Serial.print(rfid.uid.uidByte[i], HEX);
}
Serial.println();
}
rfid.PICC_HaltA();
rfid.PCD_StopCrypto1();
}
}
}
Do the similar steps as the above, and then tap one by one tag on RFID-RC522 module. The result on Serial Monitor looks like below:
Tap RFID/NFC tag on reader
Authorized Tag 2
Authorized Tag 1
You can extend the above code for three, four, or more tags.
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