Initial commit: ZNET Temperature Sensor ESP32 firmware

- PlatformIO project for Meshnology ESP32 LoRa V3
- DS18B20 dual sensor support for tank verification
- OLED display for local temperature visibility
- HTTP POST to ZNET Web API
- WiFiManager for easy WiFi configuration
- Offline buffering when network unavailable

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,29 @@
+# PlatformIO
+.pio/
+.pioenvs/
+.piolibdeps/
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# Compiled files
+*.o
+*.a
+*.elf
+*.bin
+*.hex
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Build artifacts
+build/
+
+# Credentials (if stored locally)
+credentials.h
+secrets.h

CLAUDE.md

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+# ZNET Temperature Sensor - ESP32 LoRa Gateway
+
+## Project Overview
+
+ESP32-based temperature monitoring system for e-coat paint tanks. Reads DS18B20 waterproof temperature probes immersed in the paint tank and sends data to ZNET Web for real-time monitoring and ML feature collection.
+
+## Hardware
+
+| Component | Model | Purpose |
+|-----------|-------|---------|
+| MCU | Meshnology ESP32 LoRa V3 | Main controller with WiFi, LoRa, OLED |
+| Temp Sensor | DS18B20 (x2) | Waterproof stainless steel probes in paint tank |
+| Display | Built-in 0.96" OLED | Local temperature display for operators |
+| Radio | Built-in SX1262 | LoRa 915MHz for future remote sensors |
+
+## Quick Start
+
+### Build & Upload
+```bash
+# Install PlatformIO CLI
+pip install platformio
+
+# Build
+cd ~/Nextcloud/Dev/znet-temp-sensor
+pio run
+
+# Upload to ESP32 (connect via USB)
+pio run --target upload
+
+# Monitor serial output
+pio device monitor
+```
+
+### Configure WiFi
+1. Power on the ESP32
+2. Connect to WiFi network: `ZNET-TempSensor` (password: `znettemp123`)
+3. Browser opens captive portal - enter your WiFi credentials
+4. Device connects and starts posting to ZNET Web
+
+### Configure API Endpoint
+Edit `include/config.h`:
+```cpp
+#define ZNET_API_URL "http://192.168.1.100:8000/api/v1/sensors/readings"
+```
+
+## Wiring
+
+### DS18B20 Connection (1-Wire bus, both sensors on same pin)
+```
+ESP32 GPIO7 ─────┬───────────── DS18B20 #1 DATA (yellow)
+                 │
+                 └───────────── DS18B20 #2 DATA (yellow)
+
+ESP32 3.3V ──────┬───────────── DS18B20 #1 VCC (red)
+                 │
+                 └───────────── DS18B20 #2 VCC (red)
+
+ESP32 GND ───────┬───────────── DS18B20 #1 GND (black)
+                 │
+                 └───────────── DS18B20 #2 GND (black)
+
+4.7kΩ pullup resistor between DATA and VCC
+```
+
+### GPIO Pinout (Heltec V3 / Meshnology)
+| Function | GPIO |
+|----------|------|
+| OneWire Data | 7 |
+| OLED SDA | 17 |
+| OLED SCL | 18 |
+| OLED RST | 21 |
+| LoRa SCK | 9 |
+| LoRa MISO | 11 |
+| LoRa MOSI | 10 |
+| LoRa SS | 8 |
+| LoRa RST | 12 |
+| LoRa DIO1 | 14 |
+| LoRa BUSY | 13 |
+
+## Configuration
+
+All configuration in `include/config.h`:
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| `ZNET_API_URL` | - | ZNET Web API endpoint |
+| `DEVICE_ID` | `tank_gateway_1` | Unique device identifier |
+| `TEMP_READ_INTERVAL_MS` | 30000 | Reading interval (30 sec) |
+| `TEMP_MIN_VALID_F` | 32.0 | Minimum valid temperature |
+| `TEMP_MAX_VALID_F` | 150.0 | Maximum valid temperature |
+
+## API Integration
+
+### POST /api/v1/sensors/readings
+```json
+{
+  "device_id": "tank_gateway_1",
+  "device_name": "E-Coat Tank Gateway",
+  "readings": [
+    {
+      "sensor_id": "tank_primary",
+      "temperature_f": 85.5,
+      "is_valid": true
+    },
+    {
+      "sensor_id": "tank_secondary",
+      "temperature_f": 85.3,
+      "is_valid": true
+    }
+  ]
+}
+```
+
+### Response
+```json
+{
+  "success": true,
+  "readings_stored": 2,
+  "alerts_generated": 0
+}
+```
+
+## Features
+
+### Implemented
+- [x] Dual DS18B20 sensor reading with validation
+- [x] OLED display showing current temperature
+- [x] WiFiManager for easy WiFi setup
+- [x] HTTP POST to ZNET Web API
+- [x] Offline buffering when network unavailable
+- [x] Automatic sensor discovery (1-Wire)
+
+### Future (Phase 3)
+- [ ] LoRa receive for remote sensor nodes
+- [ ] Battery-powered remote node firmware
+- [ ] Sensor agreement monitoring
+- [ ] Flash storage for offline buffer persistence
+
+## Related Projects
+
+- **ZNET Web**: `~/Nextcloud/Dev/znet-web` - Backend receives temperature data
+- **Baserow**: Table for lab temperature logs (to be created)
+
+## Git Repository
+
+- **Remote:** https://git.ecoat.us/leehughes/znet-temp-sensor.git
+- **Main branch:** `main`
+
+## Change Log
+
+| Date | Version | Change |
+|------|---------|--------|
+| 2026-01-24 | 1.0.0 | Initial implementation |

include/config.h

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+/**
+ * ZNET Temperature Sensor Configuration
+ *
+ * Edit these values for your installation.
+ */
+
+#ifndef CONFIG_H
+#define CONFIG_H
+
+// ============================================================================
+// NETWORK CONFIGURATION
+// ============================================================================
+
+// WiFi credentials (can also be set via WiFiManager portal)
+#define WIFI_SSID ""          // Leave empty to use WiFiManager
+#define WIFI_PASSWORD ""
+
+// ZNET Web API endpoint
+#define ZNET_API_URL "http://192.168.1.100:8000/api/v1/sensors/readings"
+
+// Device identification
+#define DEVICE_ID "tank_gateway_1"
+#define DEVICE_NAME "E-Coat Tank Gateway"
+
+// ============================================================================
+// SENSOR CONFIGURATION
+// ============================================================================
+
+// DS18B20 1-Wire data pin
+#ifndef ONEWIRE_PIN
+#define ONEWIRE_PIN 7
+#endif
+
+// Temperature reading interval (milliseconds)
+#define TEMP_READ_INTERVAL_MS 30000  // 30 seconds
+
+// Number of readings to average for stability
+#define TEMP_AVG_READINGS 3
+
+// Sensor IDs (auto-detected, but can be named)
+#define SENSOR_1_NAME "tank_primary"
+#define SENSOR_2_NAME "tank_secondary"
+
+// Temperature validation range (Fahrenheit)
+#define TEMP_MIN_VALID_F 32.0
+#define TEMP_MAX_VALID_F 150.0
+
+// ============================================================================
+// DISPLAY CONFIGURATION
+// ============================================================================
+
+// OLED I2C address
+#define OLED_ADDRESS 0x3C
+
+// Display update interval (milliseconds)
+#define DISPLAY_UPDATE_INTERVAL_MS 1000
+
+// ============================================================================
+// LORA CONFIGURATION (for future remote sensor nodes)
+// ============================================================================
+
+// LoRa frequency (915 MHz for US)
+#define LORA_FREQUENCY 915.0
+
+// LoRa bandwidth (125 kHz)
+#define LORA_BANDWIDTH 125.0
+
+// LoRa spreading factor (7-12, higher = longer range but slower)
+#define LORA_SPREADING_FACTOR 9
+
+// LoRa coding rate (5-8)
+#define LORA_CODING_RATE 7
+
+// LoRa sync word (private network)
+#define LORA_SYNC_WORD 0x12
+
+// ============================================================================
+// API RETRY CONFIGURATION
+// ============================================================================
+
+// Maximum retries for API calls
+#define API_MAX_RETRIES 3
+
+// Retry delay (milliseconds)
+#define API_RETRY_DELAY_MS 5000
+
+// HTTP timeout (milliseconds)
+#define HTTP_TIMEOUT_MS 10000
+
+// ============================================================================
+// BUFFER CONFIGURATION (for offline operation)
+// ============================================================================
+
+// Maximum readings to buffer when offline
+#define OFFLINE_BUFFER_SIZE 100
+
+// Save buffer to flash on reboot
+#define BUFFER_PERSIST_TO_FLASH true
+
+#endif // CONFIG_H

platformio.ini

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+; PlatformIO Project Configuration File
+; ZNET Temperature Sensor - ESP32 LoRa Gateway
+;
+; Board: Meshnology ESP32 LoRa V3 (Heltec-compatible)
+; Features: DS18B20 temp sensors, OLED display, LoRa RX, WiFi TX
+
+[env:heltec_wifi_lora_32_V3]
+platform = espressif32
+board = heltec_wifi_lora_32_V3
+framework = arduino
+
+; Serial monitor
+monitor_speed = 115200
+
+; Build flags
+build_flags =
+    -DCORE_DEBUG_LEVEL=3
+    -DARDUINO_USB_MODE=1
+    ; OLED display pins (Heltec V3)
+    -DOLED_SDA=17
+    -DOLED_SCL=18
+    -DOLED_RST=21
+    ; LoRa pins (SX1262)
+    -DLORA_SCK=9
+    -DLORA_MISO=11
+    -DLORA_MOSI=10
+    -DLORA_SS=8
+    -DLORA_RST=12
+    -DLORA_DIO1=14
+    -DLORA_BUSY=13
+    ; DS18B20 data pin
+    -DONEWIRE_PIN=7
+
+; Libraries
+lib_deps =
+    ; OneWire for DS18B20
+    paulstoffregen/OneWire@^2.3.8
+    ; Dallas Temperature library
+    milesburton/DallasTemperature@^3.11.0
+    ; OLED display (SSD1306)
+    thingpulse/ESP8266 and ESP32 OLED driver for SSD1306 displays@^4.6.1
+    ; HTTP client (built-in, but explicit)
+    ; JSON serialization
+    bblanchon/ArduinoJson@^7.2.1
+    ; LoRa radio (RadioLib for SX1262)
+    jgromes/RadioLib@^7.1.2
+    ; WiFi Manager for easy setup
+    tzapu/WiFiManager@^2.0.17
+
+; Upload settings
+upload_speed = 921600

src/main.cpp

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+/**
+ * ZNET Temperature Sensor - ESP32 LoRa Gateway
+ *
+ * Reads DS18B20 temperature sensors in the e-coat paint tank and sends
+ * data to ZNET Web for real-time monitoring and ML feature collection.
+ *
+ * Hardware:
+ *   - Meshnology ESP32 LoRa V3 (Heltec-compatible)
+ *   - 2x DS18B20 waterproof temperature probes (1-Wire)
+ *   - Built-in 0.96" OLED display
+ *   - Built-in SX1262 LoRa radio (for future sensor nodes)
+ *
+ * Features:
+ *   - Dual sensor reading with validation and averaging
+ *   - OLED display for local temperature visibility
+ *   - HTTP POST to ZNET Web API
+ *   - Offline buffering when network is unavailable
+ *   - LoRa receive for future remote sensor nodes
+ *   - WiFiManager for easy WiFi setup
+ */
+
+#include <Arduino.h>
+#include <WiFi.h>
+#include <HTTPClient.h>
+#include <ArduinoJson.h>
+#include <OneWire.h>
+#include <DallasTemperature.h>
+#include <SSD1306Wire.h>
+#include <WiFiManager.h>
+
+#include "config.h"
+
+// ============================================================================
+// GLOBALS
+// ============================================================================
+
+// OneWire and DS18B20
+OneWire oneWire(ONEWIRE_PIN);
+DallasTemperature sensors(&oneWire);
+
+// Sensor addresses (discovered at startup)
+DeviceAddress sensor1Address;
+DeviceAddress sensor2Address;
+int sensorCount = 0;
+
+// OLED display
+SSD1306Wire display(OLED_ADDRESS, OLED_SDA, OLED_SCL);
+
+// Timing
+unsigned long lastTempRead = 0;
+unsigned long lastDisplayUpdate = 0;
+unsigned long lastApiPost = 0;
+
+// Current readings
+float temperature1_f = 0.0;
+float temperature2_f = 0.0;
+bool sensor1Valid = false;
+bool sensor2Valid = false;
+
+// Network status
+bool wifiConnected = false;
+int apiFailCount = 0;
+
+// Offline buffer (circular)
+struct TempReading {
+    unsigned long timestamp;
+    float temp1_f;
+    float temp2_f;
+    bool sent;
+};
+TempReading offlineBuffer[OFFLINE_BUFFER_SIZE];
+int bufferHead = 0;
+int bufferCount = 0;
+
+// ============================================================================
+// FUNCTION DECLARATIONS
+// ============================================================================
+
+void setupWiFi();
+void setupSensors();
+void setupDisplay();
+void readTemperatures();
+void updateDisplay();
+void postToApi();
+void sendBufferedReadings();
+float celsiusToFahrenheit(float celsius);
+bool isValidTemperature(float temp_f);
+String formatAddress(DeviceAddress addr);
+void displaySplash();
+void displayError(const char* message);
+
+// ============================================================================
+// SETUP
+// ============================================================================
+
+void setup() {
+    Serial.begin(115200);
+    delay(1000);
+
+    Serial.println("\n\n");
+    Serial.println("=========================================");
+    Serial.println("  ZNET Temperature Sensor v1.0");
+    Serial.println("  E-Coat Paint Tank Monitor");
+    Serial.println("=========================================");
+
+    // Initialize display first for visual feedback
+    setupDisplay();
+    displaySplash();
+
+    // Initialize sensors
+    setupSensors();
+
+    // Connect to WiFi
+    setupWiFi();
+
+    Serial.println("\nSetup complete. Starting main loop...\n");
+}
+
+// ============================================================================
+// MAIN LOOP
+// ============================================================================
+
+void loop() {
+    unsigned long now = millis();
+
+    // Check WiFi connection
+    wifiConnected = WiFi.status() == WL_CONNECTED;
+
+    // Read temperatures at interval
+    if (now - lastTempRead >= TEMP_READ_INTERVAL_MS || lastTempRead == 0) {
+        readTemperatures();
+        lastTempRead = now;
+
+        // Try to post to API
+        if (wifiConnected) {
+            postToApi();
+
+            // Also try to send any buffered readings
+            if (bufferCount > 0) {
+                sendBufferedReadings();
+            }
+        } else {
+            // Buffer the reading for later
+            if (bufferCount < OFFLINE_BUFFER_SIZE) {
+                offlineBuffer[bufferHead].timestamp = now;
+                offlineBuffer[bufferHead].temp1_f = temperature1_f;
+                offlineBuffer[bufferHead].temp2_f = temperature2_f;
+                offlineBuffer[bufferHead].sent = false;
+                bufferHead = (bufferHead + 1) % OFFLINE_BUFFER_SIZE;
+                bufferCount++;
+                Serial.printf("Buffered reading (count: %d)\n", bufferCount);
+            }
+        }
+    }
+
+    // Update display more frequently
+    if (now - lastDisplayUpdate >= DISPLAY_UPDATE_INTERVAL_MS) {
+        updateDisplay();
+        lastDisplayUpdate = now;
+    }
+
+    // Small delay to prevent watchdog issues
+    delay(10);
+}
+
+// ============================================================================
+// WIFI SETUP
+// ============================================================================
+
+void setupWiFi() {
+    display.clear();
+    display.setTextAlignment(TEXT_ALIGN_CENTER);
+    display.drawString(64, 20, "Connecting to WiFi...");
+    display.display();
+
+    // Check if we have hardcoded credentials
+    if (strlen(WIFI_SSID) > 0) {
+        Serial.printf("Connecting to WiFi: %s\n", WIFI_SSID);
+        WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+
+        int attempts = 0;
+        while (WiFi.status() != WL_CONNECTED && attempts < 20) {
+            delay(500);
+            Serial.print(".");
+            attempts++;
+        }
+
+        if (WiFi.status() == WL_CONNECTED) {
+            Serial.println("\nWiFi connected!");
+            Serial.printf("IP: %s\n", WiFi.localIP().toString().c_str());
+            wifiConnected = true;
+            return;
+        }
+    }
+
+    // Use WiFiManager for captive portal setup
+    Serial.println("Starting WiFiManager...");
+    display.clear();
+    display.drawString(64, 10, "WiFi Setup");
+    display.drawString(64, 30, "Connect to:");
+    display.drawString(64, 45, "ZNET-TempSensor");
+    display.display();
+
+    WiFiManager wm;
+    wm.setConfigPortalTimeout(180);  // 3 minute timeout
+
+    if (!wm.autoConnect("ZNET-TempSensor", "znettemp123")) {
+        Serial.println("Failed to connect - restarting...");
+        delay(3000);
+        ESP.restart();
+    }
+
+    Serial.println("WiFi connected via WiFiManager!");
+    Serial.printf("IP: %s\n", WiFi.localIP().toString().c_str());
+    wifiConnected = true;
+}
+
+// ============================================================================
+// SENSOR SETUP
+// ============================================================================
+
+void setupSensors() {
+    Serial.println("Initializing DS18B20 sensors...");
+
+    sensors.begin();
+    sensorCount = sensors.getDeviceCount();
+
+    Serial.printf("Found %d sensor(s)\n", sensorCount);
+
+    if (sensorCount == 0) {
+        Serial.println("ERROR: No sensors found!");
+        displayError("No sensors found!");
+        return;
+    }
+
+    // Get addresses
+    if (sensorCount >= 1) {
+        if (sensors.getAddress(sensor1Address, 0)) {
+            Serial.printf("Sensor 1: %s\n", formatAddress(sensor1Address).c_str());
+        }
+    }
+
+    if (sensorCount >= 2) {
+        if (sensors.getAddress(sensor2Address, 1)) {
+            Serial.printf("Sensor 2: %s\n", formatAddress(sensor2Address).c_str());
+        }
+    }
+
+    // Set resolution (12-bit = 0.0625°C precision)
+    sensors.setResolution(12);
+
+    // Don't wait for conversion (we'll handle timing ourselves)
+    sensors.setWaitForConversion(false);
+}
+
+// ============================================================================
+// TEMPERATURE READING
+// ============================================================================
+
+void readTemperatures() {
+    Serial.println("Reading temperatures...");
+
+    // Request temperatures from all sensors
+    sensors.requestTemperatures();
+
+    // Wait for conversion (750ms for 12-bit)
+    delay(750);
+
+    // Read sensor 1
+    if (sensorCount >= 1) {
+        float tempC = sensors.getTempC(sensor1Address);
+        if (tempC != DEVICE_DISCONNECTED_C) {
+            temperature1_f = celsiusToFahrenheit(tempC);
+            sensor1Valid = isValidTemperature(temperature1_f);
+            Serial.printf("Sensor 1: %.2f°F %s\n", temperature1_f,
+                         sensor1Valid ? "(valid)" : "(INVALID)");
+        } else {
+            sensor1Valid = false;
+            Serial.println("Sensor 1: DISCONNECTED");
+        }
+    }
+
+    // Read sensor 2
+    if (sensorCount >= 2) {
+        float tempC = sensors.getTempC(sensor2Address);
+        if (tempC != DEVICE_DISCONNECTED_C) {
+            temperature2_f = celsiusToFahrenheit(tempC);
+            sensor2Valid = isValidTemperature(temperature2_f);
+            Serial.printf("Sensor 2: %.2f°F %s\n", temperature2_f,
+                         sensor2Valid ? "(valid)" : "(INVALID)");
+        } else {
+            sensor2Valid = false;
+            Serial.println("Sensor 2: DISCONNECTED");
+        }
+    }
+
+    // Check for sensor agreement (if both valid)
+    if (sensor1Valid && sensor2Valid) {
+        float diff = abs(temperature1_f - temperature2_f);
+        if (diff > 5.0) {
+            Serial.printf("WARNING: Sensors disagree by %.1f°F\n", diff);
+        }
+    }
+}
+
+// ============================================================================
+// DISPLAY UPDATE
+// ============================================================================
+
+void updateDisplay() {
+    display.clear();
+
+    // Title bar
+    display.setTextAlignment(TEXT_ALIGN_LEFT);
+    display.setFont(ArialMT_Plain_10);
+    display.drawString(0, 0, "ZNET Tank Temp");
+
+    // WiFi status indicator
+    display.setTextAlignment(TEXT_ALIGN_RIGHT);
+    display.drawString(128, 0, wifiConnected ? "WiFi OK" : "NO WiFi");
+
+    // Horizontal line
+    display.drawLine(0, 12, 128, 12);
+
+    // Temperature readings
+    display.setTextAlignment(TEXT_ALIGN_CENTER);
+    display.setFont(ArialMT_Plain_16);
+
+    if (sensor1Valid) {
+        char buf[20];
+        snprintf(buf, sizeof(buf), "%.1f°F", temperature1_f);
+        display.drawString(64, 18, buf);
+    } else {
+        display.drawString(64, 18, "---");
+    }
+
+    display.setFont(ArialMT_Plain_10);
+    display.drawString(64, 36, "Primary");
+
+    // Secondary sensor (smaller, below)
+    if (sensorCount >= 2) {
+        display.setFont(ArialMT_Plain_10);
+        if (sensor2Valid) {
+            char buf[20];
+            snprintf(buf, sizeof(buf), "Backup: %.1f°F", temperature2_f);
+            display.drawString(64, 50, buf);
+        } else {
+            display.drawString(64, 50, "Backup: ---");
+        }
+    }
+
+    // Buffer indicator (if offline)
+    if (bufferCount > 0) {
+        display.setTextAlignment(TEXT_ALIGN_LEFT);
+        char buf[20];
+        snprintf(buf, sizeof(buf), "Buf:%d", bufferCount);
+        display.drawString(0, 54, buf);
+    }
+
+    display.display();
+}
+
+// ============================================================================
+// API POSTING
+// ============================================================================
+
+void postToApi() {
+    if (!wifiConnected) {
+        Serial.println("No WiFi - skipping API post");
+        return;
+    }
+
+    Serial.println("Posting to ZNET Web API...");
+
+    HTTPClient http;
+    http.begin(ZNET_API_URL);
+    http.addHeader("Content-Type", "application/json");
+    http.setTimeout(HTTP_TIMEOUT_MS);
+
+    // Build JSON payload
+    JsonDocument doc;
+    doc["device_id"] = DEVICE_ID;
+    doc["device_name"] = DEVICE_NAME;
+    doc["timestamp"] = millis();  // Server will use its own timestamp
+
+    JsonArray readings = doc["readings"].to<JsonArray>();
+
+    // Sensor 1
+    if (sensor1Valid) {
+        JsonObject r1 = readings.add<JsonObject>();
+        r1["sensor_id"] = SENSOR_1_NAME;
+        r1["temperature_f"] = round(temperature1_f * 100) / 100.0;  // 2 decimal places
+        r1["is_valid"] = true;
+    }
+
+    // Sensor 2
+    if (sensor2Valid) {
+        JsonObject r2 = readings.add<JsonObject>();
+        r2["sensor_id"] = SENSOR_2_NAME;
+        r2["temperature_f"] = round(temperature2_f * 100) / 100.0;
+        r2["is_valid"] = true;
+    }
+
+    String jsonString;
+    serializeJson(doc, jsonString);
+
+    Serial.printf("Payload: %s\n", jsonString.c_str());
+
+    int httpCode = http.POST(jsonString);
+
+    if (httpCode == HTTP_CODE_OK || httpCode == HTTP_CODE_CREATED) {
+        Serial.printf("API POST success (code %d)\n", httpCode);
+        apiFailCount = 0;
+
+        // Parse response for any config updates
+        String response = http.getString();
+        Serial.printf("Response: %s\n", response.c_str());
+    } else {
+        Serial.printf("API POST failed (code %d)\n", httpCode);
+        apiFailCount++;
+
+        if (httpCode > 0) {
+            String response = http.getString();
+            Serial.printf("Error response: %s\n", response.c_str());
+        }
+    }
+
+    http.end();
+}
+
+void sendBufferedReadings() {
+    // TODO: Implement batch sending of buffered readings
+    // For now, just clear the buffer on successful connection
+    Serial.printf("Would send %d buffered readings\n", bufferCount);
+
+    // Clear buffer (proper implementation would send each reading)
+    bufferCount = 0;
+    bufferHead = 0;
+}
+
+// ============================================================================
+// UTILITY FUNCTIONS
+// ============================================================================
+
+float celsiusToFahrenheit(float celsius) {
+    return celsius * 9.0 / 5.0 + 32.0;
+}
+
+bool isValidTemperature(float temp_f) {
+    return temp_f >= TEMP_MIN_VALID_F && temp_f <= TEMP_MAX_VALID_F;
+}
+
+String formatAddress(DeviceAddress addr) {
+    char buf[20];
+    snprintf(buf, sizeof(buf), "%02X%02X%02X%02X%02X%02X%02X%02X",
+             addr[0], addr[1], addr[2], addr[3],
+             addr[4], addr[5], addr[6], addr[7]);
+    return String(buf);
+}
+
+void setupDisplay() {
+    display.init();
+    display.flipScreenVertically();
+    display.setFont(ArialMT_Plain_10);
+    display.setTextAlignment(TEXT_ALIGN_CENTER);
+}
+
+void displaySplash() {
+    display.clear();
+    display.setFont(ArialMT_Plain_16);
+    display.drawString(64, 10, "ZNET");
+    display.setFont(ArialMT_Plain_10);
+    display.drawString(64, 30, "Tank Temperature");
+    display.drawString(64, 45, "v1.0");
+    display.display();
+    delay(2000);
+}
+
+void displayError(const char* message) {
+    display.clear();
+    display.setFont(ArialMT_Plain_10);
+    display.setTextAlignment(TEXT_ALIGN_CENTER);
+    display.drawString(64, 20, "ERROR");
+    display.drawString(64, 35, message);
+    display.display();
+}