Arduino Uno R4 Wi-Fi Based RFID Attendance System

1* Beginner-friendly RFID Attendance (RC522 + 20x4 I2C LCD)
2   For Arduino Uno R4 Wi-Fi (pinout same as UNO-compatible boards)
3   Wiring (Arduino UNO/R4):
4     RC522: SDA(SS)=D10, SCK=D13, MOSI=D11, MISO=D12, RST=D9, 3.3V, GND
5     I2C LCD: SDA=A4, SCL=A5, VCC=5V, GND=GND
6
7   Changes in this version:
8    - Removed duplicate UID entry.
9    - Updated student names list to new names.
10*/
11
12#include <Wire.h>
13#include <SPI.h>
14#include <MFRC522.h>
15#include <LiquidCrystal_I2C.h>
16
17#define SS_PIN 10   // SDA/SS for RC522
18#define RST_PIN 9   // RST for RC522
19
20#define LCD_ADDR 0x27
21#define LCD_COLS 20
22#define LCD_ROWS 4
23
24MFRC522 rfid(SS_PIN, RST_PIN);
25LiquidCrystal_I2C lcd(LCD_ADDR, LCD_COLS, LCD_ROWS);
26
27// teacher UID (uppercase, no spaces)
28const char TEACHER_UID[] = "2A7E17B1";
29
30// 10 minutes = 10 * 60 * 1000 milliseconds
31const unsigned long ATTENDANCE_LENGTH = 10UL * 60UL * 1000UL;
32
33// debounce time to avoid reading same card many times quickly
34const unsigned long DEBOUNCE = 1000UL;
35
36// how long to show a student's info (ms)
37const unsigned long SHOW_MS = 1500UL;
38
39// small refresh rate for live timer (ms)
40const unsigned long REFRESH_MS = 500UL;
41
42// --- Student UID list and matching names ---
43// Duplicate UID removed — ensure all UIDs here are unique (uppercase, no spaces)
44const char* uids[] = {
45  "E2D2D500",
46  "49F1DF00",
47  "5C55D500",
48  "827ED600",
49  "310AF400",
50  "D7CFE000",
51  "23370EAA",
52  "7EB6F300",
53  "D784D500"
54};
55
56const char* names[] = {
57  "Amanjeet Kaur",
58  "Siddharth Verma",
59  "Meera Patel",
60  "Arjun Khanna",
61  "Neha Rathi",
62  "Vikram Singh",
63  "Simran Kaur",
64  "Ritik Sharma",
65  "Kavya Menon"
66};
67
68const int NUM = sizeof(uids) / sizeof(uids[0]);
69
70// attendance state: 0=absent, 1=on time, 2=late
71uint8_t attendance[NUM];
72
73// timing vars
74unsigned long startTime = 0;
75bool windowStarted = false;
76
77// helpers for debounce and display refresh
78String lastUID = "";
79unsigned long lastUIDTime = 0;
80unsigned long lastRefresh = 0;
81
82void setup() {
83  Serial.begin(9600);
84  while (!Serial) { } // waits for Serial on some boards, harmless on UNO/R4
85
86  SPI.begin();
87  rfid.PCD_Init();
88
89  lcd.init();
90  lcd.backlight();
91  lcd.clear();
92
93  // welcome message
94  lcd.setCursor(0, 0);
95  lcd.print("Welcome to the");
96  lcd.setCursor(0, 1);
97  lcd.print("RFID attendance");
98  lcd.setCursor(0, 2);
99  lcd.print("system");
100  delay(2000);
101
102  // start attendance window now
103  lcd.clear();
104  lcd.setCursor(0,0);
105  lcd.print("Ready for attendance");
106  startTime = millis();
107  windowStarted = true;
108
109  // mark everyone absent initially
110  for (int i = 0; i < NUM; i++) attendance[i] = 0;
111
112  // show initial timer immediately
113  updateTimerOnLCD();
114  Serial.println("Attendance started.");
115}
116
117void loop() {
118  unsigned long now = millis();
119
120  // update the live countdown at intervals
121  if (now - lastRefresh >= REFRESH_MS) {
122    updateTimerOnLCD();
123    lastRefresh = now;
124  }
125
126  // check for a new card
127  if (!rfid.PICC_IsNewCardPresent()) return;
128  if (!rfid.PICC_ReadCardSerial()) return;
129
130  // build UID string (HEX uppercase, no spaces)
131  String uid = "";
132  for (byte i = 0; i < rfid.uid.size; i++) {
133    if (rfid.uid.uidByte[i] < 0x10) uid += "0";
134    uid += String(rfid.uid.uidByte[i], HEX);
135  }
136  uid.toUpperCase();
137
138  // simple debounce: ignore if same card scanned within DEBOUNCE ms
139  if (uid == lastUID && (now - lastUIDTime) < DEBOUNCE) {
140    rfid.PICC_HaltA();
141    rfid.PCD_StopCrypto1();
142    return;
143  }
144  lastUID = uid;
145  lastUIDTime = now;
146
147  Serial.print("Card scanned: ");
148  Serial.println(uid);
149
150  // teacher card -> show summary of all students
151  if (uid == String(TEACHER_UID)) {
152    showSummary();
153    rfid.PICC_HaltA();
154    rfid.PCD_StopCrypto1();
155    updateTimerOnLCD();
156    return;
157  }
158
159  // find student index
160  int idx = findIndex(uid.c_str());
161  if (idx < 0) {
162    // unknown card
163    lcd.clear();
164    lcd.setCursor(0,0);
165    lcd.print("Unknown card:");
166    lcd.setCursor(0,1);
167    lcd.print(uid);
168    lcd.setCursor(0,3);
169    lcd.print("Not registered");
170    Serial.println("Unknown UID - not registered.");
171    delay(SHOW_MS);
172    updateTimerOnLCD();
173    rfid.PICC_HaltA();
174    rfid.PCD_StopCrypto1();
175    return;
176  }
177
178  // if already marked, just display status again
179  if (attendance[idx] != 0) {
180    showStudent(idx);
181    delay(SHOW_MS);
182    updateTimerOnLCD();
183    rfid.PICC_HaltA();
184    rfid.PCD_StopCrypto1();
185    return;
186  }
187
188  // determine if scan is inside the attendance window
189  bool onTime = windowStarted && ((now - startTime) <= ATTENDANCE_LENGTH);
190  if (onTime) attendance[idx] = 1; // on time
191  else attendance[idx] = 2;        // late
192
193  // show student info
194  showStudent(idx);
195  delay(SHOW_MS);
196  updateTimerOnLCD();
197
198  rfid.PICC_HaltA();
199  rfid.PCD_StopCrypto1();
200}
201
202// find index of uid in uids[]; return -1 if not found
203int findIndex(const char* uid) {
204  for (int i = 0; i < NUM; i++) {
205    if (strcmp(uids[i], uid) == 0) return i;
206  }
207  return -1;
208}
209
210// show ready screen and live remaining time
211void updateTimerOnLCD() {
212  lcd.clear();
213  lcd.setCursor(0,0);
214  lcd.print("Ready for attendance");
215
216  if (windowStarted) {
217    long elapsed = (long)(millis() - startTime);
218    long remaining = (long)ATTENDANCE_LENGTH - elapsed;
219    if (remaining > 0) {
220      unsigned long seconds = remaining / 1000UL;
221      unsigned int mins = seconds / 60UL;
222      unsigned int secs = seconds % 60UL;
223
224      lcd.setCursor(0,1);
225      // print "Time left: mm:ss" with leading zero for seconds
226      lcd.print("Time left: ");
227      if (mins < 10) lcd.print('0');
228      lcd.print(mins);
229      lcd.print(':');
230      if (secs < 10) lcd.print('0');
231      lcd.print(secs);
232    } else {
233      lcd.setCursor(0,1);
234      lcd.print("Attendance closed");
235    }
236  } else {
237    lcd.setCursor(0,1);
238    lcd.print("Window not set");
239  }
240
241  // clear lower lines for neatness
242  lcd.setCursor(0,2); lcd.print("                    ");
243  lcd.setCursor(0,3); lcd.print("                    ");
244}
245
246// show one student's info on LCD
247void showStudent(int i) {
248  lcd.clear();
249  lcd.setCursor(0,0);
250  lcd.print(names[i]);    // name
251  lcd.setCursor(0,1);
252  lcd.print("Present");
253  lcd.setCursor(0,2);
254  if (attendance[i] == 1) {
255    lcd.print("ON time");
256    Serial.print(names[i]); Serial.println(" -> ON time");
257  } else {
258    lcd.print("Came late");
259    Serial.print(names[i]); Serial.println(" -> Came late");
260  }
261}
262
263// show one-by-one summary for teacher (Name + Present/Absent + On time/ Late)
264void showSummary() {
265  for (int i = 0; i < NUM; i++) {
266    lcd.clear();
267    lcd.setCursor(0,0);
268    lcd.print(names[i]);
269    if (attendance[i] == 0) {
270      lcd.setCursor(0,1);
271      lcd.print("Absent");
272      Serial.print(names[i]); Serial.println(": Absent");
273    } else if (attendance[i] == 1) {
274      lcd.setCursor(0,1);
275      lcd.print("Present");
276      lcd.setCursor(0,2);
277      lcd.print("ON time");
278      Serial.print(names[i]); Serial.println(": Present (ON time)");
279    } else {
280      lcd.setCursor(0,1);
281      lcd.print("Present");
282      lcd.setCursor(0,2);
283      lcd.print("Late");
284      Serial.print(names[i]); Serial.println(": Present (Late)");
285    }
286
287    delay(2500); // pause 2.5 seconds per student
288  }
289}