feat: implement DHT22 sensor driver (#2)

examples/dht22_example/dht22_example.ino

@@ -0,0 +1,97 @@
+/**
+ * DHT22 Example - Basic Temperature and Humidity Reading
+ * 
+ * Demonstrates basic usage of DHT22Driver with error handling.
+ */
+#include <Arduino.h>
+#include <DHT22Driver.h>
+
+// Initialize DHT22 on GPIO 4
+// Default: 3 retries with 2-second delay
+DHT22Driver sensor(4);
+
+void setup() {
+    Serial.begin(115200);
+    delay(100);
+
+    Serial.println("========================================");
+    Serial.println("🌡️  DHT22 Example - MicroClaw");
+    Serial.println("========================================");
+
+    // Initialize sensor
+    sensor.begin();
+
+    Serial.println("✅ Sensor initialized");
+    Serial.println("⏳ Waiting 2 seconds for sensor warmup...");
+    delay(2000);
+}
+
+void loop() {
+    Serial.println("\n--- Reading DHT22 ---");
+
+    // Method 1: Read temperature and humidity separately
+    float temp = sensor.readTemperature();
+    float humidity = sensor.readHumidity();
+
+    if (sensor.isOK()) {
+        Serial.printf("🌡️  Temperature: %.1f°C (%.1f°F)\n", temp, temp * 9.0/5.0 + 32.0);
+        Serial.printf("💧 Humidity: %.1f%%\n", humidity);
+
+        // Calculate heat index (feels-like temperature)
+        float heatIndex = computeHeatIndex(temp, humidity);
+        Serial.printf("🔥 Heat Index: %.1f°C\n", heatIndex);
+
+        // Comfort level
+        String comfort = getComfortLevel(temp, humidity);
+        Serial.printf("😊 Comfort: %s\n", comfort.c_str());
+    } else {
+        Serial.println("❌ Error: " + sensor.getError());
+    }
+
+    // Method 2: Read as JSON (for MQTT/HTTP reporting)
+    Serial.println("\n--- JSON Output ---");
+    String json = sensor.readJSON();
+    Serial.println(json);
+
+    // Wait 5 seconds before next reading
+    // DHT22 sensor needs 2+ seconds between reads
+    delay(5000);
+}
+
+/**
+ * Compute heat index (feels-like temperature)
+ * Simplified Steadman formula
+ */
+float computeHeatIndex(float temp, float humidity) {
+    float T = temp;
+    float RH = humidity;
+
+    float HI = -8.78469475556 + 
+               1.61139411 * T + 
+               2.33854883889 * RH + 
+               -0.14611605 * T * RH + 
+               -0.012308094 * T * T + 
+               -0.0164248277778 * RH * RH + 
+               0.002211732 * T * T * RH + 
+               0.00072546 * T * RH * RH + 
+               -0.000003582 * T * T * RH * RH;
+
+    return HI;
+}
+
+/**
+ * Get comfort level based on temperature and humidity
+ */
+String getComfortLevel(float temp, float humidity) {
+    if (temp < 15.0) {
+        return "Cold";
+    } else if (temp > 30.0) {
+        return "Hot";
+    } else if (humidity < 30.0) {
+        return "Dry";
+    } else if (humidity > 70.0) {
+        return "Humid";
+    } else {
+        return "Comfortable";
+    }
+}

lib/DHT22Driver/DHT22Driver.cpp

@@ -0,0 +1,125 @@
+#include "DHT22Driver.h"
+
+DHT22Driver::DHT22Driver(uint8_t pin, uint8_t retries, uint16_t retryDelay)
+    : dht(pin, DHT22), pin(pin), maxRetries(retries), retryDelay(retryDelay), lastReadOK(false), lastError("") {
+}
+
+void DHT22Driver::begin() {
+    dht.begin();
+    lastReadOK = false;
+    lastError = "";
+}
+
+float DHT22Driver::readTemperature() {
+    float temp, humidity;
+    if (readWithRetry(temp, humidity)) {
+        return temp;
+    }
+    return NAN;
+}
+
+float DHT22Driver::readTemperatureF() {
+    float temp = readTemperature();
+    if (!isnan(temp)) {
+        return temp * 9.0 / 5.0 + 32.0;
+    }
+    return NAN;
+}
+
+float DHT22Driver::readHumidity() {
+    float temp, humidity;
+    if (readWithRetry(temp, humidity)) {
+        return humidity;
+    }
+    return NAN;
+}
+
+bool DHT22Driver::read(float &temp, float &humidity) {
+    return readWithRetry(temp, humidity);
+}
+
+String DHT22Driver::readJSON() {
+    float temp, humidity;
+
+    if (readWithRetry(temp, humidity)) {
+        String json = "{";
+        json += "\"temperature\":" + String(temp, 1) + ",";
+        json += "\"humidity\":" + String(humidity, 1) + ",";
+        json += "\"status\":\"ok\"";
+        json += "}";
+        return json;
+    } else {
+        String json = "{";
+        json += "\"error\":\"" + lastError + "\",";
+        json += "\"status\":\"error\"";
+        json += "}";
+        return json;
+    }
+}
+
+bool DHT22Driver::isOK() {
+    return lastReadOK;
+}
+
+String DHT22Driver::getError() {
+    return lastError;
+}
+
+bool DHT22Driver::readWithRetry(float &temp, float &humidity) {
+    for (uint8_t attempt = 0; attempt < maxRetries; attempt++) {
+        // Read from sensor
+        humidity = dht.readHumidity();
+        temp = dht.readTemperature();
+
+        // Check if read succeeded
+        if (!isnan(humidity) && !isnan(temp)) {
+            // Validate reasonable ranges
+            if (temp < -40.0 || temp > 80.0) {
+                lastError = "Temperature out of range: " + String(temp, 1) + "C";
+                lastReadOK = false;
+
+                if (attempt < maxRetries - 1) {
+                    delay(retryDelay);
+                    continue;
+                }
+                return false;
+            }
+
+            if (humidity < 0.0 || humidity > 100.0) {
+                lastError = "Humidity out of range: " + String(humidity, 1) + "%";
+                lastReadOK = false;
+
+                if (attempt < maxRetries - 1) {
+                    delay(retryDelay);
+                    continue;
+                }
+                return false;
+            }
+
+            // Success!
+            lastReadOK = true;
+            lastError = "";
+            return true;
+        }
+
+        // Read failed, set error message
+        if (isnan(humidity) && isnan(temp)) {
+            lastError = "Sensor read failed (both values NaN)";
+        } else if (isnan(humidity)) {
+            lastError = "Humidity read failed (NaN)";
+        } else {
+            lastError = "Temperature read failed (NaN)";
+        }
+
+        lastReadOK = false;
+
+        // Retry if not last attempt
+        if (attempt < maxRetries - 1) {
+            delay(retryDelay);
+        }
+    }
+
+    // All retries exhausted
+    lastError += " after " + String(maxRetries) + " attempts";
+    return false;
+}

lib/DHT22Driver/DHT22Driver.h

@@ -0,0 +1,101 @@
+#ifndef DHT22DRIVER_H
+#define DHT22DRIVER_H
+
+#include <Arduino.h>
+#include <DHT.h>
+
+/**
+ * DHT22Driver - Temperature and Humidity Sensor Driver
+ * 
+ * Wrapper around Adafruit DHT library with error handling,
+ * JSON output, and configurable retry logic.
+ * 
+ * Usage:
+ *   DHT22Driver sensor(4);  // GPIO 4
+ *   sensor.begin();
+ *   
+ *   float temp = sensor.readTemperature();
+ *   float humidity = sensor.readHumidity();
+ *   
+ *   String json = sensor.readJSON();
+ */
+class DHT22Driver {
+public:
+    /**
+     * Constructor
+     * @param pin GPIO pin connected to DHT22 DATA pin
+     * @param retries Number of read retries on failure (default: 3)
+     * @param retryDelay Delay between retries in ms (default: 2000)
+     */
+    DHT22Driver(uint8_t pin, uint8_t retries = 3, uint16_t retryDelay = 2000);
+
+    /**
+     * Initialize the sensor
+     * Call this in setup()
+     */
+    void begin();
+
+    /**
+     * Read temperature in Celsius
+     * @return Temperature or NaN on error
+     */
+    float readTemperature();
+
+    /**
+     * Read temperature in Fahrenheit
+     * @return Temperature or NaN on error
+     */
+    float readTemperatureF();
+
+    /**
+     * Read relative humidity (%)
+     * @return Humidity or NaN on error
+     */
+    float readHumidity();
+
+    /**
+     * Read temperature and humidity together (more efficient)
+     * @param temp Output parameter for temperature (C)
+     * @param humidity Output parameter for humidity (%)
+     * @return true on success, false on error
+     */
+    bool read(float &temp, float &humidity);
+
+    /**
+     * Read temperature and humidity and return as JSON
+     * Format: {"temperature":25.0,"humidity":60.0,"status":"ok"}
+     * or: {"error":"Sensor read failed","status":"error"}
+     * @return JSON string
+     */
+    String readJSON();
+
+    /**
+     * Check if last read was successful
+     * @return true if last read succeeded
+     */
+    bool isOK();
+
+    /**
+     * Get error message from last failed read
+     * @return Error message or empty string if no error
+     */
+    String getError();
+
+private:
+    DHT dht;
+    uint8_t pin;
+    uint8_t maxRetries;
+    uint16_t retryDelay;
+    bool lastReadOK;
+    String lastError;
+
+    /**
+     * Internal read with retry logic
+     * @param temp Output parameter for temperature
+     * @param humidity Output parameter for humidity
+     * @return true on success, false after all retries exhausted
+     */
+    bool readWithRetry(float &temp, float &humidity);
+};
+
+#endif // DHT22DRIVER_H