2026-10-15 22:42:46 +02:00
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# How it works
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[← Back to the README](../README.md)
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1. **ESP32 boot.** The ESP32 connects to WiFi and starts ArduinoOTA. After a crash it
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runs only OTA for 15 seconds, and after repeated crashes it goes to safe mode. Bad OTA
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firmware is rolled back automatically, see
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[Keeping OTA alive](../src/esp32/README.md#keeping-ota-alive). It then switches the display relay on, waits for
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the Nano's `READY` message (at most 3 s), shows "Connecting...", starts NTP and
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connects to MQTT.
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2. **Clock.** Once the time is synced, the ESP32 sends a new frame whenever the screen
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changes, mostly once a minute:
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- **08:00–22:00:** the page: the chosen page (by default the built-in Clock page,
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Pikachu with a thought bubble showing `HH:MM`, yawning from 17:00), or what the
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[schedule and rules](web-ui.md#schedule) pick.
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- **22:00–23:30:** the clock is only shown during the minutes :00, :15, :30 and :45.
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30 seconds after each of those minutes, the relay turns the display off.
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- **23:31–08:00:** the screen is cleared (or shows the off image chosen in the web UI)
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and power is cut after 30 seconds.
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3. **Home Assistant**: switches, dropdowns and sensors over MQTT, see
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[Home Assistant](home-assistant.md).
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4. **Nano.** The Nano reads commands from the serial line and updates its frame buffer.
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2026-10-16 15:20:26 +02:00
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On `D` it flips only the dots that changed, in small steps so it never stops reading
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the serial port. Every 2 minutes (Settings, "Dot refresh") it flips every dot once
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more to fix dots that did not flip.
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5. **Frame check.** After a frame the ESP asks the Nano for a checksum of its image and
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compares it with what it sent. When they differ (lost bytes can shift the picture),
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the Nano doesn't answer, or it restarted, the ESP sends the whole image again. It also
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does that every 10 minutes (Settings, "Image resync"); only dots that differ flip, so
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normally nothing changes. The counts are on the System tab.
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2026-10-15 22:42:46 +02:00
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The serial protocol is described in [src/nano/README.md](../src/nano/README.md).
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