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firmware/esp32c3-arduino/README.md

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+# Arduino variant for ESP32C3
+
+This firmware is designed to run on the [LilyGO T-01C3](https://lilygo.cc/products/t-01c3?srsltid=AfmBOopddAvO0gTIFNYZyTcoF1PxQjxZ0YAxuhoQviz9i5j4B0WOdg4l) board and serves as a drop-in replacement for the original ESP8266-based Nixie clock firmware.
+
+**Compared to the ESP8266, the ESP32C3 provides much better clock accuracy and reliability, thanks to its advanced hardware and improved timekeeping features.**
+If you received a Nixie clock from me, you are eligible for a free hardware upgrade - just contact me!
+
+This firmware features a high refresh rate display with advanced dimming and blending effects, leveraging the ESP32's RMT (Remote Control) peripheral for precise timing and smooth transitions.
+
+## Highlights
+
+- **High Refresh Rate:** Achieves smooth digit transitions and flicker-free display using RMT hardware
+- **Dimming & Blending:** Configurable dimming and blending for night mode and digit transitions
+- **WiFiManager Configuration:** Easily configure all clock options via a web portal
+- **Prometheus Metrics:** Exposes runtime and system metrics for monitoring
+
+## Configuration Options via WiFiManager
+
+- **NTP Time Server:** Set the network time server for clock synchronization
+- **City:** Select your city for timezone presets
+- **Timezone:** Manually specify the POSIX timezone string
+- **Display Mode:** Choose between time, date, or alternating time/date display
+- **Dimming Duty Cycle:** Adjust brightness for night mode
+- **Dimming Start/End:** Set hours for automatic dimming
+- **Blending Duration:** Control the duration of digit blending transitions
+- **Hour Format:** Select 12-hour or 24-hour display
+
+## Prometheus Metrics
+
+The firmware exposes the following metrics for monitoring:
+
+- `nixie_boot_timestamp_seconds`: Boot time of the device
+- `nixie_last_ntp_sync_timestamp_seconds`: Last successful NTP synchronization
+- `nixie_littlefs_total_bytes`: Total LittleFS storage size
+- `nixie_littlefs_used_bytes`: Used LittleFS storage
+- `nixie_uptime_seconds`: Device uptime
+- `nixie_display_task_iterations_total`: Number of display task iterations
+- `nixie_ntp_sync_count_total`: Number of NTP sync events
+- `nixie_wifi_manager_process_count_total`: Number of WiFiManager process events
+
+## Advanced Features
+
+- **Automatic NTP Sync:** Periodically synchronizes time with the configured NTP server
+- **Stale NTP Detection:** Blinks all digits and colons if NTP sync is stale
+- **Critical Section Display Updates:** Uses FreeRTOS and portMUX for safe, high-speed display updates
+
+## Getting Started
+
+1. Flash the firmware to your ESP32-C3
+2. Connect to the WiFiManager AP (SSID is based on device MAC)
+3. Configure your clock settings via the web portal
+4. Monitor metrics via Prometheus-compatible tools
+
+---
+
+For more details, see the source code and comments.