RFID Based Attendance System Using ESP32

What You’ll Build in This Project:

The system reads RFID tags and uploads attendance data instantly to Firebase and Google Sheets, offering secure storage and easy reporting. It’s beginner-friendly with clear steps, making it simple to build.

The user selects ESP32 for its low cost (about 350 rupees) and built-in Wi-Fi, which supports real-time cloud syncing. Its powerful dual-core processor and Arduino IDE support make it ideal for affordable, scalable RFID attendance projects.

How the system tracks attendance

The ESP32 reads each RFID scan and sent in real time to both cloud databases, stamped with date and time. The system auto-retries if Wi-Fi drops, blocks unauthorized scans, and lets admins view up-to-date attendance from anywhere.

Components and Tools Required

Hardware list (ESP32, MFRC522 RFID module, etc.)

ESP32 microcontroller board
MFRC522 RFID reader module
RFID cards or tags
Jumper wires
Breadboard or PCB for connections
Optional: OLED or LCD display for feedback

All components are low-cost and available online or at electronics stores, letting you build this system on a student budget.

Software list (Arduino IDE, libraries)

Arduino IDE (free download)
ESP32 board support via Board Manager
MFRC522 library for RFID
WiFi and HTTPClient libraries for networking
Optionally, Adafruit SSD1306 or LCD library for display

These libraries are free, well-supported, and make coding much faster and easier for all levels of users.

Cloud accounts (Firebase, Google Sheets)

Free Firebase account for realtime database storage
Free Google Sheets account via Google
Both accounts are easy to set up and provide secure cloud hosting for attendance logs

No paid service needed, and setup can be completed in minutes with a standard Google login.

System Circuit Design and Wiring

ESP32 RFID RC522 attendance system on vertical breadboard with OLED display showing RFID system ready.

MFRC522 RFID Module to ESP32 NodeMCU 30-Pin

RFID Module Pin	ESP32 Pin Label	Description
VCC	3V3	Power (3.3V only)
GND	GND	Ground
RST	D4	Reset pin
IRQ	Not connected	Leave empty
MISO	D19	Master In Slave Out
MOSI	D23	Master Out Slave In
SCK	D18	Serial Clock
SDA/SS	D5	Slave Select

0.96″ OLED Display (I2C) to ESP32 NodeMCU

OLED Pin	ESP32 Pin Label	Description
GND	GND	Ground
VDD	3V3	Power (3.3V)
SCK	D22	I2C Clock
SDA	D21	I2C Data

Visual Wiring Diagram:

ESP32 NodeMCU 30-Pin
│
├── 3V3 ──┬── RFID VCC
│         └── OLED VDD
│
├── GND ──┬── RFID GND
│         └── OLED GND
│
├── D4 ─────── RFID RST
├── D5 ─────── RFID SDA/SS
├── D18 ────── RFID SCK
├── D19 ────── RFID MISO
├── D21 ────── OLED SDA
├── D22 ────── OLED SCK
└── D23 ────── RFID MOSI

ESP32 NodeMCU 30-Pin
│
├── 3V3 ──┬── RFID VCC
│         └── OLED VDD
│
├── GND ──┬── RFID GND
│         └── OLED GND
│
├── D4 ─────── RFID RST
├── D5 ─────── RFID SDA/SS
├── D18 ────── RFID SCK
├── D19 ────── RFID MISO
├── D21 ────── OLED SDA
├── D22 ────── OLED SCK
└── D23 ────── RFID MOSI

Pin Definitions for Arduino Code:

// RFID pins
#define RST_PIN 4    // D4
#define SS_PIN 5     // D5
// MISO = D19 (GPIO19)
// MOSI = D23 (GPIO23)
// SCK = D18 (GPIO18)

// OLED pins (I2C)
#define OLED_SDA 21  // D21
#define OLED_SCL 22  // D22

// RFID pins
#define RST_PIN 4    // D4
#define SS_PIN 5     // D5
// MISO = D19 (GPIO19)
// MOSI = D23 (GPIO23)
// SCK = D18 (GPIO18)

// OLED pins (I2C)
#define OLED_SDA 21  // D21
#define OLED_SCL 22  // D22

Double-Check Your Connections

Before powering on, verify:

✅ RFID VCC and OLED VDD both go to 3V3 (NOT 5V)
✅ All GND pins are connected together
✅ RFID RST is on D4 (separate from OLED)
✅ OLED SCK on D22, SDA on D21
✅ RFID SPI pins: D5, D18, D19, D23
✅ All wires are firmly inserted (wiggle test them)

Check Our ESP32 Pinout Guide: https://learniot.in/esp32-pinout-reference/

Setting Up Arduino IDE and ESP32

Adding ESP32 board to Arduino IDE

Adding ESP32 board to Arduino IDE:

Open Arduino IDE
Go to File → Preferences
Add this URL to “Additional Board Manager URLs”: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
Go to Tools → Board → Board Manager
Search “ESP32” and install “ESP32 by Espressif Systems“
Select Tools → Board → ESP32 Arduino → ESP32 Dev Module

Installing required libraries (MFRC522, WiFi, HTTPClient)

Go to Sketch → Include Library → Manage Libraries, then install:

MFRC522 (for RFID)
Adafruit GFX Library (for OLED)
Adafruit SSD1306 (for OLED)
WiFi (built-in with ESP32)
HTTPClient (built-in with ESP32)
ArduinoJson (for Firebase/Sheets data formatting)

Common setup issues and fixes

If you don’t see the ESP32 board in the list, double-check the Board Manager URL and install updates. If the COM port isn’t detected or uploads fail, install the CP2102 or CH340 driver (depending on your ESP32 model). Press and hold the “BOOT” button during upload if you see a “Timeout” or “Failed to connect” error. A quick IDE restart often solves library issues—it’s usually something small!.

Firebase and Google Sheets Integration

Creating Firebase Realtime Database

Go to firebase.google.com
Create new project
Enable Realtime Database
Set rules to test mode (for now)
Copy your Database URL and API Key

Setting up Google Sheets API:

Step 1: Prepare Google Sheet

Create new Google Sheet with columns in Row 1:

Step 2: Add Apps Script:

function doGet(e) {
  return handleRequest(e);
}

function doPost(e) {
  return handleRequest(e);
}

function handleRequest(e) {
  try {
    var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
    var params = e.parameter;
    
    var name = params.name || "Unknown";
    var uid = params.uid || "Unknown";
    var timestamp = params.time || new Date().toLocaleTimeString();
    var date = new Date().toLocaleDateString();
    
    // Append new row: Name, Card ID, Date, Time
    sheet.appendRow([name, uid, date, timestamp]);
    
    return ContentService.createTextOutput(
      JSON.stringify({"result": "Success"})
    ).setMimeType(ContentService.MimeType.JSON);
  }
  catch(error) {
    return ContentService.createTextOutput(
      JSON.stringify({"result": "Error", "message": error.toString()})
    ).setMimeType(ContentService.MimeType.JSON);
  }
}

function doGet(e) {
  return handleRequest(e);
}

function doPost(e) {
  return handleRequest(e);
}

function handleRequest(e) {
  try {
    var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
    var params = e.parameter;
    
    var name = params.name || "Unknown";
    var uid = params.uid || "Unknown";
    var timestamp = params.time || new Date().toLocaleTimeString();
    var date = new Date().toLocaleDateString();
    
    // Append new row: Name, Card ID, Date, Time
    sheet.appendRow([name, uid, date, timestamp]);
    
    return ContentService.createTextOutput(
      JSON.stringify({"result": "Success"})
    ).setMimeType(ContentService.MimeType.JSON);
  }
  catch(error) {
    return ContentService.createTextOutput(
      JSON.stringify({"result": "Error", "message": error.toString()})
    ).setMimeType(ContentService.MimeType.JSON);
  }
}

Step 3: Deploy Web App

Click Deploy → New deployment
Choose “Web app” as deployment type
Set Execute as: Me (your Google account)
Set Who has access: Anyone
Click Deploy
Copy the Web App URL

Step 4: Use Deployment URL in ESP32 Code

Example HTTP GET request from ESP32 to Google Sheets:

https://script.google.com/macros/s/YOUR_SCRIPT_ID/exec?uid=A1B2C3D4&time=12:45pm&name=John%20Doe

https://script.google.com/macros/s/YOUR_SCRIPT_ID/exec?uid=A1B2C3D4&time=12:45pm&name=John%20Doe

Replace ESP32 code with your URL (remember to URL-encode names if needed). The webhook will automatically append data into the Google Sheet.

Coding the ESP32 for RFID Attendance

Full Arduino Sketch (Copy-Paste Ready)

#include <SPI.h>
#include <MFRC522.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <ArduinoJson.h>

#define RST_PIN 4   // D4
#define SS_PIN 5    // D5

MFRC522 rfid(SS_PIN, RST_PIN);

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ===== CONFIGURE THESE =====
const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_WIFI_PASSWORD";

String firebaseUrl = "YOUR_PROJECT.firebaseio.com";
String firebaseKey = "YOUR_FIREBASE_SECRET";

String sheetsUrl = "YOUR_GOOGLE_APPS_SCRIPT_URL";

// Function prototypes
void connectWiFi();
void showReady();
void showScanning(String uid);
void showSuccess(String uid);
void showError();
void showMessage(String line1, String line2, String line3);
String getUID();
String getTime();
bool sendFirebase(String uid, String time);
bool sendSheets(String uid, String time);

void setup() {
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED failed");
    while(1);
  }
  
  connectWiFi();
  showReady();
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) connectWiFi();
  
  if (rfid.PICC_IsNewCardPresent() && rfid.PICC_ReadCardSerial()) {
    String uid = getUID();
    
    showScanning(uid);
    
    String time = getTime();
    
    if (sendFirebase(uid, time) && sendSheets(uid, time)) {
      showSuccess(uid);
    } else {
      showError();
    }
    
    delay(3000);
    showReady();
    
    rfid.PICC_HaltA();
  }
  delay(200);
}

String getUID() {
  String uid = "";
  for (byte i = 0; i < rfid.uid.size; i++) {
    uid += rfid.uid.uidByte[i] < 0x10 ? "0" : "";
    uid += String(rfid.uid.uidByte[i], HEX);
  }
  uid.toUpperCase();
  return uid;
}

String getTime() {
  return String(millis());
}

void connectWiFi() {
  WiFi.begin(ssid, password);
  showMessage("Connecting WiFi", "...", "");
  
  int i = 0;
  while (WiFi.status() != WL_CONNECTED && i < 20) {
    delay(500);
    Serial.print(".");
    i++;
  }
  Serial.println();
  Serial.print("IP: ");
  Serial.println(WiFi.localIP());
}

bool sendFirebase(String uid, String time) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    String url = "https://" + firebaseUrl + "/attendance.json?auth=" + firebaseKey;
    
    StaticJsonDocument<200> doc;
    doc["uid"] = uid;
    doc["time"] = time;
    
    String json;
    serializeJson(doc, json);
    
    http.begin(url);
    http.addHeader("Content-Type", "application/json");
    int code = http.POST(json);
    http.end();
    
    Serial.print("Firebase: ");
    Serial.println(code);
    
    return (code == 200 || code == 201);
  }
  return false;
}

bool sendSheets(String uid, String time) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    String url = sheetsUrl + "?uid=" + uid + "&time=" + time;
    http.begin(url);
    int code = http.GET();
    http.end();
    
    Serial.print("Sheets: ");
    Serial.println(code);
    
    return (code == 200 || code == 302);
  }
  return false;
}

void showReady() {
  showMessage("Attendance Ready", "Scan Card", "");
}

void showScanning(String uid) {
  showMessage("Scanning", uid, "Processing...");
}

void showSuccess(String uid) {
  showMessage("SUCCESS", uid, "Saved!");
}

void showError() {
  showMessage("ERROR", "Check WiFi", "or Cloud");
}

void showMessage(String line1, String line2, String line3) {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 15);
  display.println(line1);
  display.setCursor(0, 35);
  display.println(line2);
  if (line3 != "") {
    display.setCursor(0, 50);
    display.println(line3);
  }
  display.display();
}

#include <SPI.h>
#include <MFRC522.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <ArduinoJson.h>

#define RST_PIN 4   // D4
#define SS_PIN 5    // D5

MFRC522 rfid(SS_PIN, RST_PIN);

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ===== CONFIGURE THESE =====
const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_WIFI_PASSWORD";

String firebaseUrl = "YOUR_PROJECT.firebaseio.com";
String firebaseKey = "YOUR_FIREBASE_SECRET";

String sheetsUrl = "YOUR_GOOGLE_APPS_SCRIPT_URL";

// Function prototypes
void connectWiFi();
void showReady();
void showScanning(String uid);
void showSuccess(String uid);
void showError();
void showMessage(String line1, String line2, String line3);
String getUID();
String getTime();
bool sendFirebase(String uid, String time);
bool sendSheets(String uid, String time);

void setup() {
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED failed");
    while(1);
  }
  
  connectWiFi();
  showReady();
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) connectWiFi();
  
  if (rfid.PICC_IsNewCardPresent() && rfid.PICC_ReadCardSerial()) {
    String uid = getUID();
    
    showScanning(uid);
    
    String time = getTime();
    
    if (sendFirebase(uid, time) && sendSheets(uid, time)) {
      showSuccess(uid);
    } else {
      showError();
    }
    
    delay(3000);
    showReady();
    
    rfid.PICC_HaltA();
  }
  delay(200);
}

String getUID() {
  String uid = "";
  for (byte i = 0; i < rfid.uid.size; i++) {
    uid += rfid.uid.uidByte[i] < 0x10 ? "0" : "";
    uid += String(rfid.uid.uidByte[i], HEX);
  }
  uid.toUpperCase();
  return uid;
}

String getTime() {
  return String(millis());
}

void connectWiFi() {
  WiFi.begin(ssid, password);
  showMessage("Connecting WiFi", "...", "");
  
  int i = 0;
  while (WiFi.status() != WL_CONNECTED && i < 20) {
    delay(500);
    Serial.print(".");
    i++;
  }
  Serial.println();
  Serial.print("IP: ");
  Serial.println(WiFi.localIP());
}

bool sendFirebase(String uid, String time) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    String url = "https://" + firebaseUrl + "/attendance.json?auth=" + firebaseKey;
    
    StaticJsonDocument<200> doc;
    doc["uid"] = uid;
    doc["time"] = time;
    
    String json;
    serializeJson(doc, json);
    
    http.begin(url);
    http.addHeader("Content-Type", "application/json");
    int code = http.POST(json);
    http.end();
    
    Serial.print("Firebase: ");
    Serial.println(code);
    
    return (code == 200 || code == 201);
  }
  return false;
}

bool sendSheets(String uid, String time) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    String url = sheetsUrl + "?uid=" + uid + "&time=" + time;
    http.begin(url);
    int code = http.GET();
    http.end();
    
    Serial.print("Sheets: ");
    Serial.println(code);
    
    return (code == 200 || code == 302);
  }
  return false;
}

void showReady() {
  showMessage("Attendance Ready", "Scan Card", "");
}

void showScanning(String uid) {
  showMessage("Scanning", uid, "Processing...");
}

void showSuccess(String uid) {
  showMessage("SUCCESS", uid, "Saved!");
}

void showError() {
  showMessage("ERROR", "Check WiFi", "or Cloud");
}

void showMessage(String line1, String line2, String line3) {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 15);
  display.println(line1);
  display.setCursor(0, 35);
  display.println(line2);
  if (line3 != "") {
    display.setCursor(0, 50);
    display.println(line3);
  }
  display.display();
}

BEFORE UPLOADING – UPDATE THESE 3 LINES:

Line 22-23: WiFi credentials

const char* ssid = "YourHomeWiFi";
const char* password = "YourWiFiPassword";

const char* ssid = "YourHomeWiFi";
const char* password = "YourWiFiPassword";

Line 25-26: Firebase config

String firebaseUrl = "yourproject.firebaseio.com";
String firebaseKey = "your_api_key_here";

String firebaseUrl = "yourproject.firebaseio.com";
String firebaseKey = "your_api_key_here";

Line 28: Google Sheets URL

String sheetsUrl = "https://script.google.com/macros/s/YOUR_SCRIPT_ID/exec";

String sheetsUrl = "https://script.google.com/macros/s/YOUR_SCRIPT_ID/exec";

Uploading, Testing & Debugging

Uploading your code to ESP32

Select Board: Tools → Board → ESP32 Arduino → ESP32 Dev Module
Select Port: Tools → Port → COM6 (your ESP32 port)
Click Verify → Should show: 291KB (22%) of program storage
Click Upload (→ arrow icon)
If stuck at “Connecting…” → Hold BOOT button 3 seconds during upload
Success message: Hard resetting via RTS pin...

Expected output:
esptool v5.1.0 Serial port COM6
Chip type: ESP32-D0WD-V3
Writing at 0x00010000 [==========================] 100%
Hard resetting via RTS pin... ✅

Expected output:
esptool v5.1.0 Serial port COM6
Chip type: ESP32-D0WD-V3
Writing at 0x00010000 [==========================] 100%
Hard resetting via RTS pin... ✅

First RFID card scan

After upload, watch OLED sequence:

1. "Connecting WiFi..." + dots (10 seconds)
2. "Attendance Ready"  
   "Scan Card" 
3. Scan RFID card → "Scanning" + UID
4. "ERROR" (normal - no Firebase yet)

1. "Connecting WiFi..." + dots (10 seconds)
2. "Attendance Ready"  
   "Scan Card" 
3. Scan RFID card → "Scanning" + UID
4. "ERROR" (normal - no Firebase yet)

Serial Monitor (115200 baud) shows:

IP: 192.168.1.100
Card scanned: A1B2C3D4
Firebase: -1
Sheets: -1

IP: 192.168.1.100
Card scanned: A1B2C3D4
Firebase: -1
Sheets: -1

Viewing attendance in cloud

Firebase Console:

Go to console.firebase.google.com
Select your project → Realtime Database
Path: /attendance → See JSON entries appear

Google Sheets:

Open your Google Sheet
New rows auto-appear: [UID, Time, Date]

Firebase shows:
{
  "-N123abc": {
    "uid": "A1B2C3D4",
    "time": "12345678"
  }
}

Firebase shows:
{
  "-N123abc": {
    "uid": "A1B2C3D4",
    "time": "12345678"
  }
}

Debugging common errors

Error	OLED/Serial Shows	Fix
Upload fails	`Connecting....` (stuck)	Hold BOOT button 3 sec during upload
No WiFi	No dots, stays on WiFi screen	Check SSID/password spelling (case-sensitive)
No RFID	“Attendance Ready” but no scan	Check wiring: D4(RST), D5(SS), D18,19,23
OLED blank	Nothing displays	Check D21(SDA), D22(SCK), 3.3V power
“Firebase: -1”	Normal (no config yet)	Setup Firebase later
Random chars	Garbage in Serial Monitor	Wrong baud rate → Set 115200

Quick fixes:

❌ No Serial output → Tools → Serial Monitor → 115200 baud
❌ OLED shows garbage → Power cycle ESP32
❌ Multiple card reads → Increase delay(3000) to delay(5000)

❌ No Serial output → Tools → Serial Monitor → 115200 baud
❌ OLED shows garbage → Power cycle ESP32
❌ Multiple card reads → Increase delay(3000) to delay(5000)

Test checklist:

Upload successful
WiFi connects (IP in Serial Monitor)
OLED shows “Attendance Ready”
RFID card detected on scan
“ERROR” message appears (expected)

Enhancing the System

Making a web dashboard

Firebase Console = Your INSTANT Live Dashboard! (No extra hosting needed)

Step 1: Access Firebase Live Dashboard

1. Go to console.firebase.google.com
2. Select your project
3. Click "Realtime Database" → "Data" tab
4. LIVE attendance appears instantly!

1. Go to console.firebase.google.com
2. Select your project
3. Click "Realtime Database" → "Data" tab
4. LIVE attendance appears instantly!

Your data shows LIVE:

yourproject.firebaseio.com/attendance/
├── -N123abc: { "uid": "A1B2C3D4", "time": "123456" }
├── -N456def: { "uid": "B2C3D4E5", "time": "123789" }
└── Updates every card scan! 👇

yourproject.firebaseio.com/attendance/
├── -N123abc: { "uid": "A1B2C3D4", "time": "123456" }
├── -N456def: { "uid": "B2C3D4E5", "time": "123789" }
└── Updates every card scan! 👇

Step 2: Shareable Mobile Dashboard

Direct link: https://yourproject.firebaseio.com/attendance.json

✅ Phone browser → Live JSON data
✅ Bookmark for teachers
✅ No app install needed
✅ Works offline (cached)

Direct link: https://yourproject.firebaseio.com/attendance.json

✅ Phone browser → Live JSON data
✅ Bookmark for teachers
✅ No app install needed
✅ Works offline (cached)

Step 3: Google Sheets Dashboard (Automatic Reports)

Your Sheet auto-updates:
| UID       | Time     | Date        |
|-----------|----------|-------------|
| A1B2C3D4  | 23:14:23 | 27-Nov-2025 |
| B2C3D4E5  | 23:15:01 | 27-Nov-2025 |

Share: sheets.google.com → "Anyone with link"

Your Sheet auto-updates:
| UID       | Time     | Date        |
|-----------|----------|-------------|
| A1B2C3D4  | 23:14:23 | 27-Nov-2025 |
| B2C3D4E5  | 23:15:01 | 27-Nov-2025 |

Share: sheets.google.com → "Anyone with link"

Complete Dashboard System:

ESP32 → Firebase (Live JSON) + Google Sheets (Excel)
         ↓                           ↓
Firebase Console (Live)     Google Sheets (Reports)

ESP32 → Firebase (Live JSON) + Google Sheets (Excel)
         ↓                           ↓
Firebase Console (Live)     Google Sheets (Reports)

Dashboard URLs ready to share:

🔴 Live: yourproject.firebaseio.com/attendance.json
📊 Reports: docs.google.com/spreadsheets/YOUR_SHEET_ID

🔴 Live: yourproject.firebaseio.com/attendance.json
📊 Reports: docs.google.com/spreadsheets/YOUR_SHEET_ID

Real Project Experience & Troubleshooting

Wiring mistakes I actually made

❌ RFID VCC to 5V → Module fried instantly (use 3.3V only)
❌ MISO/MOSI swapped → No card detection
❌ Forgot common GND → Random resets
❌ OLED SDA to D20 → Blank screen (use D21)

❌ RFID VCC to 5V → Module fried instantly (use 3.3V only)
❌ MISO/MOSI swapped → No card detection
❌ Forgot common GND → Random resets
❌ OLED SDA to D20 → Blank screen (use D21)

RFID reader troubles & solutions

❌ "No card detected" → Check D4(RST), D5(SS), 3.3V wiring
❌ "Card read failed" → Add 10kΩ pullup on RST pin
❌ Multiple reads → Increase delay(3000) → delay(5000)
❌ Weak range → Add 100uF capacitor across RFID VCC/GND

❌ "No card detected" → Check D4(RST), D5(SS), 3.3V wiring
❌ "Card read failed" → Add 10kΩ pullup on RST pin
❌ Multiple reads → Increase delay(3000) → delay(5000)
❌ Weak range → Add 100uF capacitor across RFID VCC/GND

Preventing WiFi dropouts

unsigned long lastCheck = 0;
void loop() {
  if(millis() - lastCheck > 30000) {  // Check every 30s
    if(WiFi.status() != WL_CONNECTED) connectWiFi();
    lastCheck = millis();
  }
}

unsigned long lastCheck = 0;
void loop() {
  if(millis() - lastCheck > 30000) {  // Check every 30s
    if(WiFi.status() != WL_CONNECTED) connectWiFi();
    lastCheck = millis();
  }
}

Frequently Asked Questions

What is the maximum number of cards supported?

The ESP32 can handle over 65,000 unique RFID card UIDs—ideal for classrooms or offices.

Will it work if the WiFi goes down?

The card scan data appears on the Serial Monitor, so you don’t lose local records. For true offline storage, code could be extended to save to SD card.

Can NFC phones act as RFID cards?

Yes, using NFC stickers or compatible apps, you can register phones as valid RFID tags.

How do I add another ESP32 scanner at a different door?

Use the same Firebase and Google Sheets URLs—multiple devices will sync attendance records.

What wiring problems are most common?

Mistakes like swapping MISO/MOSI, using 5V instead of 3.3V for the RFID module, or leaving out a common ground.