feat: integrate DHT22, OLED, WiFi/MQTT with 5-level temp-driven PWM fan

Fan speed is now auto-selected from a temperature table (levels 1-5 at
28/30/32/34/36C mapping to PWM duties 230/236/242/249/255) with 1C
hysteresis. State and level are published to MQTT for Home Assistant.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -39,3 +39,4 @@ obj/
 # Dependencies and libraries
 node_modules/
 dist/
+main/secrets.h

main/main.ino

@@ -0,0 +1,183 @@
+// fan4life main
+// ESP32-C3 | Arduino core 3.x
+// 2-pin 5V fan via IRLZ44N MOSFET (PWM)
+// DHT22 temp/humidity, SSD1306 OLED, WiFi + MQTT (state publish only)
+
+#include <U8g2lib.h>
+#include <DHT.h>
+#include <WiFi.h>
+#include <PubSubClient.h>
+#include "secrets.h"
+
+// --- MQTT topics (publish only) ---
+#define TOPIC_TEMP      "esp32c3_fan/temperature"
+#define TOPIC_HUMIDITY  "esp32c3_fan/humidity"
+#define TOPIC_FAN_STATE "esp32c3_fan/fan/state"
+#define TOPIC_FAN_SPEED "esp32c3_fan/fan/speed"
+
+// --- Pins ---
+#define DHTPIN    2
+#define DHTTYPE   DHT22
+#define FAN_PIN   3
+#define OLED_SDA  5
+#define OLED_SCL  6
+
+// --- PWM ---
+#define PWM_FREQ  20000
+#define PWM_RES   8
+
+// --- Temperature -> fan level table ---
+// Level 0 = off. Higher temp -> higher level. Hysteresis: drop a level
+// only after temp falls TEMP_HYST below the level's threshold.
+#define TEMP_HYST 1.0
+struct FanLevel { const char* label; float tempOn; uint8_t duty; };
+const FanLevel LEVELS[] = {
+  { "1", 28.0, 230 },
+  { "2", 30.0, 236 },
+  { "3", 32.0, 242 },
+  { "4", 34.0, 249 },
+  { "5", 36.0, 255 },
+};
+const uint8_t NUM_LEVELS = sizeof(LEVELS) / sizeof(LEVELS[0]);
+#define TEMP_OFF (LEVELS[0].tempOn - TEMP_HYST)
+
+// --- OLED ---
+#define OLED_RESET U8X8_PIN_NONE
+U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, OLED_RESET, OLED_SCL, OLED_SDA);
+
+DHT dht(DHTPIN, DHTTYPE);
+WiFiClient wifiClient;
+PubSubClient mqtt(wifiClient);
+
+int xOffset = 30;
+int yOffset = 30;
+
+uint8_t fanLevel = 0;  // 0 = off, 1..NUM_LEVELS
+
+void applyFan() {
+  if (fanLevel == 0) {
+    ledcWrite(FAN_PIN, 0);
+    return;
+  }
+  uint8_t duty = LEVELS[fanLevel - 1].duty;
+  if (duty > 0 && duty < 200) {
+    ledcWrite(FAN_PIN, 255);  // kick-start
+    delay(300);
+  }
+  ledcWrite(FAN_PIN, duty);
+}
+
+void publishFan() {
+  mqtt.publish(TOPIC_FAN_STATE, fanLevel > 0 ? "ON" : "OFF", true);
+  const char* label = fanLevel > 0 ? LEVELS[fanLevel - 1].label : "0";
+  mqtt.publish(TOPIC_FAN_SPEED, label, true);
+}
+
+void setFanLevel(uint8_t level) {
+  if (level == fanLevel) return;
+  fanLevel = level;
+  applyFan();
+  publishFan();
+}
+
+// Pick the level for a given temperature, with hysteresis from current level.
+uint8_t levelForTemp(float tempC) {
+  uint8_t target = 0;
+  for (uint8_t i = 0; i < NUM_LEVELS; i++) {
+    if (tempC >= LEVELS[i].tempOn) target = i + 1;
+  }
+  // Hysteresis: only drop if temp is clearly below the current level's on-point.
+  if (target < fanLevel) {
+    float dropBelow = LEVELS[fanLevel - 1].tempOn - TEMP_HYST;
+    if (tempC > dropBelow) target = fanLevel;
+  }
+  return target;
+}
+
+void connectWiFi() {
+  Serial.printf("Connecting to %s", WIFI_SSID);
+  WiFi.begin(WIFI_SSID, WIFI_PASS);
+  while (WiFi.status() != WL_CONNECTED) {
+    delay(500); Serial.print(".");
+  }
+  Serial.printf("\nWiFi connected: %s\n", WiFi.localIP().toString().c_str());
+}
+
+void connectMQTT() {
+  while (!mqtt.connected()) {
+    Serial.print("Connecting MQTT...");
+    if (mqtt.connect(MQTT_CLIENT, MQTT_USER, MQTT_PASS)) {
+      Serial.println("connected!");
+      publishFan();
+    } else {
+      Serial.printf("failed rc=%d, retry in 5s\n", mqtt.state());
+      delay(5000);
+    }
+  }
+}
+
+void handle_oled(float tempC, float humidity) {
+  char line1[20], line2[20], line3[20];
+  snprintf(line1, sizeof(line1), "T: %.1f C", tempC);
+  snprintf(line2, sizeof(line2), "H: %.0f %%", humidity);
+  const char* lvl = fanLevel > 0 ? LEVELS[fanLevel - 1].label : "0";
+  snprintf(line3, sizeof(line3), "Fan: %s L%s",
+           fanLevel > 0 ? "ON" : "OFF", lvl);
+
+  u8g2.clearBuffer();
+  u8g2.setFont(u8g2_font_4x6_tr);
+  u8g2.drawStr(xOffset, yOffset,      line1);
+  u8g2.drawStr(xOffset, yOffset + 10, line2);
+  u8g2.drawStr(xOffset, yOffset + 20, line3);
+  u8g2.sendBuffer();
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(500);
+
+  ledcAttach(FAN_PIN, PWM_FREQ, PWM_RES);
+  ledcWrite(FAN_PIN, 0);
+
+  dht.begin();
+
+  u8g2.begin();
+  u8g2.setContrast(255);
+  u8g2.setBusClock(400000);
+  u8g2.clearDisplay();
+
+  connectWiFi();
+  mqtt.setServer(MQTT_HOST, MQTT_PORT);
+  connectMQTT();
+
+  Serial.println("Ready.");
+}
+
+void loop() {
+  if (WiFi.status() != WL_CONNECTED) connectWiFi();
+  if (!mqtt.connected()) connectMQTT();
+  mqtt.loop();
+
+  float tempC    = dht.readTemperature();
+  float humidity = dht.readHumidity();
+
+  if (isnan(tempC) || isnan(humidity)) {
+    Serial.println("DHT22 read failed");
+    delay(2000);
+    return;
+  }
+
+  // Auto fan control: temperature -> level (with hysteresis)
+  setFanLevel(levelForTemp(tempC));
+
+  // Publish telemetry
+  char buf[10];
+  dtostrf(tempC,    4, 1, buf); mqtt.publish(TOPIC_TEMP,     buf);
+  dtostrf(humidity, 4, 0, buf); mqtt.publish(TOPIC_HUMIDITY, buf);
+
+  Serial.printf("T:%.1fC  H:%.0f%%  Fan:%s L%u\n",
+                tempC, humidity, fanLevel > 0 ? "ON" : "OFF", fanLevel);
+  handle_oled(tempC, humidity);
+
+  delay(3000);
+}