Smart NFC Attendance Terminal

#include <Arduino.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <SPI.h>
#include <MFRC522.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <ArduinoJson.h>

// Replace these three values with the school network and central API details.

// Forward declarations
void printLine(uint8_t row, const String &text);
void setIndicators(bool green, bool red);
void beep(uint8_t times);
void showReady();
void showResult(const String &line1, const String &line2, bool accepted);
String cardUidHex();
void startWifiConnection();
void maintainWifi();
void sendCardEvent(const String &uid);

const char *WIFI_SSID = "YOUR_SCHOOL_WIFI";
const char *WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";
const char *API_URL = "http://YOUR_SERVER_OR_APPS_SCRIPT_ENDPOINT";
const char *TERMINAL_ID = "GATE_01";

constexpr uint8_t RFID_SS_PIN = 5;
constexpr uint8_t RFID_RST_PIN = 4;
constexpr uint8_t RFID_SCK_PIN = 18;
constexpr uint8_t RFID_MISO_PIN = 19;
constexpr uint8_t RFID_MOSI_PIN = 23;
constexpr uint8_t I2C_SDA_PIN = 21;
constexpr uint8_t I2C_SCL_PIN = 22;
constexpr uint8_t BUZZER_PIN = 25;
constexpr uint8_t GREEN_LED_PIN = 26;
constexpr uint8_t RED_LED_PIN = 32;

constexpr unsigned long SCAN_DEBOUNCE_MS = 2000;
constexpr unsigned long RESULT_SCREEN_MS = 3000;
constexpr unsigned long WIFI_RETRY_MS = 10000;

MFRC522 rfid(RFID_SS_PIN, RFID_RST_PIN);
LiquidCrystal_I2C lcd(0x27, 16, 2);

unsigned long lastScanMs = 0;
unsigned long resultUntilMs = 0;
unsigned long lastWifiAttemptMs = 0;
bool showingResult = false;

void printLine(uint8_t row, const String &text) {
  String line = text;
  if (line.length() > 16) line = line.substring(0, 16);
  while (line.length() < 16) line += ' ';
  lcd.setCursor(0, row);
  lcd.print(line);
}

void setIndicators(bool green, bool red) {
  digitalWrite(GREEN_LED_PIN, green ? HIGH : LOW);
  digitalWrite(RED_LED_PIN, red ? HIGH : LOW);
}

void beep(uint8_t times) {
  for (uint8_t i = 0; i < times; i++) {
    digitalWrite(BUZZER_PIN, HIGH);
    delay(120);
    digitalWrite(BUZZER_PIN, LOW);
    if (i + 1 < times) delay(120);
  }
}

void showReady() {
  showingResult = false;
  setIndicators(false, false);
  printLine(0, "School System");
  if (WiFi.status() == WL_CONNECTED) {
    printLine(1, "Ready: Tap Card");
  } else {
    printLine(1, "WiFi reconnecting");
  }
}

void showResult(const String &line1, const String &line2, bool accepted) {
  printLine(0, line1);
  printLine(1, line2);
  setIndicators(accepted, !accepted);
  beep(accepted ? 1 : 2);
  showingResult = true;
  resultUntilMs = millis() + RESULT_SCREEN_MS;
}

String cardUidHex() {
  String uid;
  for (byte i = 0; i < rfid.uid.size; i++) {
    if (rfid.uid.uidByte[i] < 0x10) uid += '0';
    uid += String(rfid.uid.uidByte[i], HEX);
  }
  uid.toUpperCase();
  return uid;
}

void startWifiConnection() {
  if (strlen(WIFI_SSID) == 0 || String(WIFI_SSID).startsWith("YOUR_")) return;
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  lastWifiAttemptMs = millis();
}

void maintainWifi() {
  if (WiFi.status() == WL_CONNECTED) return;
  if (millis() - lastWifiAttemptMs >= WIFI_RETRY_MS) {
    WiFi.disconnect();
    startWifiConnection();
  }
}

void sendCardEvent(const String &uid) {
  if (WiFi.status() != WL_CONNECTED) {
    showResult("Network Offline", "Try again soon", false);
    return;
  }
  if (String(API_URL).startsWith("http://YOUR_")) {
    showResult("API not set", "Set API_URL", false);
    return;
  }

  JsonDocument request;
  request["uid"] = uid;
  request["terminal_id"] = TERMINAL_ID;
  String payload;
  serializeJson(request, payload);

  HTTPClient http;
  http.setTimeout(8000);
  http.begin(API_URL);
  http.addHeader("Content-Type", "application/json");
  const int httpCode = http.POST(payload);
  const String response = (httpCode > 0) ? http.getString() : "";
  http.end();

  if (httpCode != HTTP_CODE_OK) {
    showResult("Server Error", httpCode > 0 ? "HTTP " + String(httpCode) : "Request failed", false);
    return;
  }

  JsonDocument reply;
  DeserializationError error = deserializeJson(reply, response);
  if (error) {
    showResult("Server Error", "Bad JSON reply", false);
    return;
  }

  const String status = reply["status"] | "error";
  const String name = reply["name"] | "";
  const String message = reply["message"] | "";
  const bool accepted = (status == "success");

  if (!accepted) {
    showResult("Access Denied", message.length() ? message : "Request rejected", false);
    return;
  }

  String top = name.length() ? name + " (OK)" : "Accepted";
  String bottom = message;
  if (!reply["balance"].isNull()) {
    bottom = "Bal: " + String(reply["balance"].as<float>(), 0) + " THB";
  }
  if (!bottom.length()) bottom = "Checked In";
  showResult(top, bottom, true);
}

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(RED_LED_PIN, OUTPUT);
  setIndicators(false, false);
  digitalWrite(BUZZER_PIN, LOW);

  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  lcd.init();
  lcd.backlight();
  printLine(0, "School System");
  printLine(1, "Connecting WiFi");

  SPI.begin(RFID_SCK_PIN, RFID_MISO_PIN, RFID_MOSI_PIN, RFID_SS_PIN);
  rfid.PCD_Init();
  startWifiConnection();
}

void loop() {
  maintainWifi();

  if (showingResult && millis() >= resultUntilMs) showReady();
  if (showingResult) return;

  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;
  if (millis() - lastScanMs < SCAN_DEBOUNCE_MS) {
    rfid.PICC_HaltA();
    rfid.PCD_StopCrypto1();
    return;
  }

  lastScanMs = millis();
  const String uid = cardUidHex();
  rfid.PICC_HaltA();
  rfid.PCD_StopCrypto1();
  printLine(0, "Card detected");
  printLine(1, "Contacting server");
  sendCardEvent(uid);
}