D1 mini + SCD30 CO₂ Monitor (ESP8266) — OLED + Web + UDP

A tiny CO₂ monitor for Wemos/LOLIN D1 mini (ESP8266) + Sensirion SCD30 with a 128×64 SSD1309 OLED.
It provides a dark-mode web UI (with WiFiManager captive portal), a live brightness slider, and UDP telemetry/controls.

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Used hardware

• Wemos/LOLIN D1 mini (ESP8266)
• Sensirion SCD30 CO₂ / Temperature / Humidity sensor (I²C)
• 128×64 OLED, monochrome, SSD1309 controller (I²C)
• Optional: LM2596 buck/step-down converter (if powering from >3.3 V)

Input voltage: 3.3 V (logic).

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Wiring

docs/wiring.png

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Required libraries (Arduino Library Manager)

• WiFiManager (tzapu)
• SparkFun SCD30 Arduino Library
• U8g2 (olikraus)
• ArduinoJson v6+ (Benoit Blanchon)
• LittleFS (bundled with ESP8266 core) for config storage

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ESP8266 board support (Boards Manager URL)

In Arduino IDE → Preferences → Additional Boards Manager URLs, add:

https://arduino.esp8266.com/stable/package_esp8266com_index.json

Then open Tools → Board → Boards Manager…, search for ESP8266 by ESP8266 Community, and install.

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Functionality breakdown

• Wi-Fi setup: WiFiManager captive portal (AP D1Mini-Setup) for first-time configuration; then auto-reconnect.
• Web UI (dark mode):
  • Status card (IP, configured UDP target and ports).
  • Brightness slider (0–100) — RAM-only; 0 turns the OLED off (power-save). Resets to 0 on reboot.
  • Settings to set:
    • UDP target IP & port (telemetry)
    • UDP listen port (brightness control)
• UDP telemetry (sender): three small packets:
  • T + temperature (°C)
  //disabled, enable by uncommenting it
  • H + humidity (%RH)
  //disabled, enable by uncommenting it
  • C + CO₂ (ppm)
• UDP brightness (receiver): listens on the configured port; accepts either:
  • ASCII integers 0..100 (e.g., "42")
  • single-byte binary values 0..100
• OLED display: large numeric CO₂ readout (ppm) for readability at distance.
• Config persistence: UDP target + ports saved in LittleFS (/config.json).
  Brightness is RAM-only to avoid flash wear; not persisted across resets.

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Build & flash

1. Install ESP8266 board support (see Boards Manager URL above).
2. Install the Required libraries via Library Manager.
3. Select Board: LOLIN(WEMOS) D1 R2 & mini.
4. Open the sketch, verify the U8g2 constructor matches your OLED.
   (SSD1309 is enabled by default; if you use SSD1306, switch the constructor.)
5. Upload.

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First run

1. On boot, the device starts an AP EagleDisplay (password config123) if it can’t join Wi-Fi.
2. Visit http://192.168.4.1/ to configure Wi-Fi (captive portal).
3. After connecting to your network, open the device’s IP to access the web UI.

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UDP details

• Telemetry target: configurable via web UI (IP + port).
• Packets: three separate UDP packets labeled T, H, and C (ASCII payload).
• Brightness control: send UDP to the listen port with value 0..100:
  • ASCII: "0", "25", "100"
  • Binary: single byte 0..100
  • 0 turns the display OFF (power-save); >0 maps to OLED contrast.

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Credits

• ESP8266 Arduino Core (ESP8266 Community)
• WiFiManager (tzapu)
• U8g2 (olikraus)
• ArduinoJson (B. Blanchon)
• SparkFun SCD30 library