RFID Music Assistant Controller

#include <Arduino.h>
#include <WiFi.h>
#include <PubSubClient.h>
#include <SPI.h>
#include <MFRC522.h>

// Replace these three values with the Wi-Fi and MQTT details used by Home Assistant.

// Forward declarations
void connectWiFi();
void connectMqtt();
String tagUid();

const char *WIFI_SSID = "YOUR_WIFI_NAME";
const char *WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";
const char *MQTT_HOST = "192.168.1.50";
const uint16_t MQTT_PORT = 1883;
const char *MQTT_USER = "";
const char *MQTT_PASSWORD = "";

const char *TAG_TOPIC = "home/rfid_reader/tag";
const char *STATUS_TOPIC = "home/rfid_reader/status";

constexpr uint8_t RC522_SCK_PIN = 4;
constexpr uint8_t RC522_MISO_PIN = 5;
constexpr uint8_t RC522_MOSI_PIN = 6;
constexpr uint8_t RC522_CS_PIN = 7;
constexpr uint8_t RC522_RST_PIN = 3;

WiFiClient wifiClient;
PubSubClient mqttClient(wifiClient);
MFRC522 rfid(RC522_CS_PIN, RC522_RST_PIN);

String lastTag = "";
unsigned long lastTagMillis = 0;
constexpr unsigned long RESCAN_DELAY_MS = 2000;

void connectWiFi() {
  if (WiFi.status() == WL_CONNECTED) return;

  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to Wi-Fi");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print('.');
  }
  Serial.println(" connected");
}

void connectMqtt() {
  while (!mqttClient.connected()) {
    String clientId = "rfid-reader-" + String((uint32_t)(ESP.getEfuseMac() & 0xFFFFFF), HEX);
    Serial.print("Connecting to MQTT");

    bool connected;
    if (strlen(MQTT_USER) > 0) {
      connected = mqttClient.connect(clientId.c_str(), MQTT_USER, MQTT_PASSWORD,
                                     STATUS_TOPIC, 0, true, "offline");
    } else {
      connected = mqttClient.connect(clientId.c_str(), STATUS_TOPIC, 0, true, "offline");
    }

    if (connected) {
      mqttClient.publish(STATUS_TOPIC, "online", true);
      Serial.println(" connected");
    } else {
      Serial.print(" failed, code ");
      Serial.println(mqttClient.state());
      delay(3000);
    }
  }
}

String tagUid() {
  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 setup() {
  Serial.begin(115200);
  SPI.begin(RC522_SCK_PIN, RC522_MISO_PIN, RC522_MOSI_PIN, RC522_CS_PIN);
  rfid.PCD_Init();
  delay(50);
  connectWiFi();
  mqttClient.setServer(MQTT_HOST, MQTT_PORT);
  Serial.println("Present an RFID card or key fob.");
}

void loop() {
  connectWiFi();
  if (!mqttClient.connected()) connectMqtt();
  mqttClient.loop();

  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;

  String uid = tagUid();
  const unsigned long now = millis();
  if (uid != lastTag || now - lastTagMillis >= RESCAN_DELAY_MS) {
    mqttClient.publish(TAG_TOPIC, uid.c_str(), false);
    Serial.print("Published RFID tag: ");
    Serial.println(uid);
    lastTag = uid;
    lastTagMillis = now;
  }

  rfid.PICC_HaltA();
  rfid.PCD_StopCrypto1();
  delay(100);
}