Attendance tracking is an essential task in schools, organizations, and workplaces, yet traditional methods such as paper-based sign-in sheets or manual entry are time-consuming and prone to errors. With the advancement of Internet of Things (IoT) technology, automated attendance systems have become more efficient, accurate, and easy to manage.
This project presents a simple attendance system using RFID cards, an ESP32 microcontroller, and Google Sheets as a cloud-based database. Each user is assigned a unique RFID card, and when the card is scanned, the ESP32 reads the card’s ID and sends the attendance data to Google Sheets via Wi-Fi. This allows attendance records to be stored automatically, securely, and accessed in real time from anywhere.
The system aims to demonstrate a low-cost, reliable, and scalable solution for attendance management while introducing basic concepts of embedded systems, wireless communication, and cloud integration.
Connections guide:
Code:
In attendance.ino :
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 16
#define RST_PIN 17
MFRC522 rfid(SS_PIN, RST_PIN);
String uidString;
#include "WiFi.h"
#include <HTTPClient.h>
const char* ssid = "DTM E-SMART"; //--> Your wifi name
const char* password = "0919890938";
// Google script Web_App_URL.
String Web_App_URL = "Replace with URL";
#define On_Board_LED_PIN 2
#define MAX_STUDENTS 10 // Max students
struct Student {
String id;
char code[10];
char name[30];
};
Student students[MAX_STUDENTS];
int studentCount = 0;
int runMode=2;
const int btnIO = 15;
bool btnIOState = HIGH;
unsigned long timeDelay=millis();
unsigned long timeDelay2=millis();
bool InOutState=0; //0: vào, 1:ra
const int ledIO = 4;
const int buzzer = 5;
void setup() {
Serial.begin(115200);
pinMode(buzzer,OUTPUT);
digitalWrite(buzzer,LOW);
pinMode(btnIO,INPUT_PULLUP);
pinMode(ledIO,OUTPUT);
pinMode(On_Board_LED_PIN,OUTPUT);
Serial.println();
Serial.println("-------------");
Serial.println("WIFI mode : STA");
Serial.println("-------------");
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while(WiFi.status() != WL_CONNECTED) {
Serial.print(".");
delay(1000);
}
if(!readDataSheet()) Serial.println("Can't read data from google sheet!");
SPI.begin(); // Init SPI bus
rfid.PCD_Init(); // Init MFRC522
}
void loop() {
if(millis()-timeDelay2>500){
readUID();
timeDelay2=millis();
}
if(digitalRead(btnIO)==LOW){
if(btnIOState==HIGH){
if(millis()-timeDelay>500){
//Thực hiện lệnh
InOutState = !InOutState;
digitalWrite(ledIO,InOutState);
timeDelay=millis();
}
btnIOState=LOW;
}
}else{
btnIOState=HIGH;
}
}
void beep(int n, int d){
for(int i=0;i<n;i++){
digitalWrite(buzzer,HIGH);
delay(d);
digitalWrite(buzzer,LOW);
delay(d);
}
}
void readUID(){
// Prepare key - all keys are set to FFFFFFFFFFFFh at chip delivery from the factory.
MFRC522::MIFARE_Key key;
for (byte i = 0; i < 6; i++) {
key.keyByte[i] = 0xFF;
}
// Look for new cards
if ( ! rfid.PICC_IsNewCardPresent()) {
return;
}
// Select one of the cards
if ( ! rfid.PICC_ReadCardSerial()) {
return;
}
// Now a card is selected. The UID and SAK is in mfrc522.uid.
uidString="";
for (byte i = 0; i < rfid.uid.size; i++) {
uidString.concat(String(rfid.uid.uidByte[i] < 0x10 ? "0" : ""));
uidString.concat(String(rfid.uid.uidByte[i], HEX));
}
uidString.toUpperCase();
Serial.println("Card UID: "+uidString);
beep(1,200);
if(runMode==1) writeUIDSheet();
else if(runMode==2) writeLogSheet();
// Dump PICC type
byte piccType = rfid.PICC_GetType(rfid.uid.sak);
// Serial.print("PICC type: ");
//Serial.println(mfrc522.PICC_GetTypeName(piccType));
if ( piccType != MFRC522::PICC_TYPE_MIFARE_MINI
&& piccType != MFRC522::PICC_TYPE_MIFARE_1K
&& piccType != MFRC522::PICC_TYPE_MIFARE_4K) {
//Serial.println("This sample only works with MIFARE Classic cards.");
return;
}
}
bool readDataSheet(){
if (WiFi.status() == WL_CONNECTED) {
digitalWrite(On_Board_LED_PIN, HIGH);
// Create a URL for reading or getting data from Google Sheets.
String Read_Data_URL = Web_App_URL + "?sts=read";
Serial.println();
Serial.println("-------------");
Serial.println("Read data from Google Spreadsheet...");
Serial.print("URL : ");
Serial.println(Read_Data_URL);
//::::::::::::::::::The process of reading or getting data from Google Sheets.
// Initialize HTTPClient as "http".
HTTPClient http;
// HTTP GET Request.
http.begin(Read_Data_URL.c_str());
http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
// Gets the HTTP status code.
int httpCode = http.GET();
Serial.print("HTTP Status Code : ");
Serial.println(httpCode);
// Getting response from google sheet.
String payload;
studentCount=0;
if (httpCode > 0) {
payload = http.getString();
Serial.println("Payload : " + payload);
// split
char charArray[payload.length() + 1];
payload.toCharArray(charArray, payload.length() + 1);
// Count
int numberOfElements = countElements(charArray, ',');
Serial.println("Number of elements: "+String(numberOfElements));
char *token = strtok(charArray, ",");
while (token != NULL && studentCount < numberOfElements/3) {
students[studentCount].id = atoi(token); // ID change
token = strtok(NULL, ",");
strcpy(students[studentCount].code, token); // Copy ID
token = strtok(NULL, ",");
strcpy(students[studentCount].name, token); // Copy name
studentCount++;
token = strtok(NULL, ",");
}
// print student list
for (int i = 0; i < studentCount; i++) {
Serial.print("ID: ");
Serial.println(students[i].id);
Serial.print("Code: ");
Serial.println(students[i].code);
Serial.print("Name: ");
Serial.println(students[i].name);
}
}
http.end();
//::::::::::::::::::
digitalWrite(On_Board_LED_PIN, LOW);
Serial.println("-------------");
if(studentCount>0) return true;
else return false;
}
}
void writeUIDSheet(){
String Send_Data_URL = Web_App_URL + "?sts=writeuid";
Send_Data_URL += "&uid=" + uidString;
Serial.println();
Serial.println("-------------");
Serial.println("Send data to Google Spreadsheet...");
Serial.print("URL : ");
Serial.println(Send_Data_URL);
// Initialize HTTPClient as "http".
HTTPClient http;
// HTTP GET Request.
http.begin(Send_Data_URL.c_str());
http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
// Gets the HTTP status code.
int httpCode = http.GET();
Serial.print("HTTP Status Code : ");
Serial.println(httpCode);
// Getting response from google sheets.
String payload;
if (httpCode > 0) {
payload = http.getString();
Serial.println("Payload : " + payload);
}
http.end();
}
void writeLogSheet(){
char charArray[uidString.length() + 1];
uidString.toCharArray(charArray, uidString.length() + 1);
char* studentName = getStudentNameById(charArray);
if (studentName != nullptr) {
Serial.print("Student name with ID ");
Serial.print(uidString);
Serial.print(" is: ");
Serial.println(studentName);
String Send_Data_URL = Web_App_URL + "?sts=writelog";
Send_Data_URL += "&uid=" + uidString;
Send_Data_URL += "&name=" + urlencode(String(studentName));
if(InOutState==0){
Send_Data_URL += "&inout="+urlencode("VÀO");
}else{
Send_Data_URL += "&inout="+urlencode("RA");
}
Serial.println();
Serial.println("-------------");
Serial.println("Send data to Google Spreadsheet...");
Serial.print("URL : ");
Serial.println(Send_Data_URL);
// Initialize HTTPClient as "http".
HTTPClient http;
// HTTP GET Request.
http.begin(Send_Data_URL.c_str());
http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
// Gets the HTTP status code.
int httpCode = http.GET();
Serial.print("HTTP Status Code : ");
Serial.println(httpCode);
// Getting response from google sheets.
String payload;
if (httpCode > 0) {
payload = http.getString();
Serial.println("Payload : " + payload);
}
http.end();
} else {
Serial.print("No student with that ID ");
Serial.println(uidString);
beep(3,500);
}
}
String urlencode(String str) {
String encodedString = "";
char c;
char code0;
char code1;
char code2;
for (int i = 0; i < str.length(); i++) {
c = str.charAt(i);
if (c == ' ') {
encodedString += '+';
} else if (isalnum(c)) {
encodedString += c;
} else {
code1 = (c & 0xf) + '0';
if ((c & 0xf) > 9) {
code1 = (c & 0xf) - 10 + 'A';
}
c = (c >> 4) & 0xf;
code0 = c + '0';
if (c > 9) {
code0 = c - 10 + 'A';
}
code2 = '\\0';
encodedString += '%';
encodedString += code0;
encodedString += code1;
}
yield();
}
return encodedString;
}
char* getStudentNameById(char* uid) {
for (int i = 0; i < studentCount; i++) {
if (strcmp(students[i].code, uid) == 0) {
return students[i].name;
}
}
return nullptr;
}
int countElements(const char* data, char delimiter) {
char dataCopy[strlen(data) + 1];
strcpy(dataCopy, data);
int count = 0;
char* token = strtok(dataCopy, &delimiter);
while (token != NULL) {
count++;
token = strtok(NULL, &delimiter);
}
return count;
}
You should also downloaded MFRC522 library on Arduino IDE
Go to Google Sheet and create new file, with two tabs within in it:
tab1: Students information