Air Quality Sensor

Air Quality Sensor

A compact, open-hardware indoor air quality monitor built around the ESP32-S3. Measures CO₂, temperature, humidity and pressure, and shows the room's air quality on a ring of RGB LEDs.

Features

• True CO₂ measurement. Sensirion SCD41 photoacoustic NDIR sensor, not an estimated eCO₂ value.
• Temperature & humidity. Sensirion SHT4x, placed on a thermally isolated PCB island (milled slot) to keep it away from heat from the MCU and regulator.
• Barometric pressure. Goertek SPA06-003.
• Wi-Fi + Bluetooth LE. ESP32-S3-WROOM-1U with an external antenna connector (U.FL).
• 16× WS2812 LED ring on the bottom side, shining through a translucent diffuser. The 5 V data line goes through a 74AHCT1G125 level shifter.
• USB-C power with ESD protection (USBLC6-2) and fuses, plus a TPS54302 buck regulator for the 3.3 V rail.
• Expansion port. JST-PH 4-pin connector with 3.3 V, GND and two free GPIOs.
• Debug UART header and test points on every important net.
• Round Ø70 mm PCB in a 3D-printable enclosure with angled ventilation slots.

Gallery

USB-C side

Bottom with LED diffuser

PCB

Top side

Bottom side – LED ring

📄 Schematic (PDF)

Hardware overview

 USB-C ──► ESD + fuse ──► TPS54302 ──► 3.3 V ─┬─► ESP32-S3 ──I²C──┬─► SCD41  (CO₂)
   │                                          │       │           ├─► SHT4x  (T / RH)
   └──────────── 5 V ─────────────────────────┼───────┼──────┐    └─► SPA06  (pressure)
                                              │       │      ▼
                                              │       └──► 74AHCT1G125 ──► 16× WS2812 ring
                                              └─► JST-PH expansion (2× GPIO)

Repository structure

.
├── 01_Hardware/
│   ├── 02_KiCad/
│   │   ├── air-quality-sensor/    # KiCad project (schematic + PCB)
│   │   │   └── production/        # Gerbers, BOM, pick & place (JLCPCB)
│   │   └── lib/                   # Custom symbols, footprints, 3D models
│   └── 03_3D_Model/
│       ├── 3D-Printing/           # Enclosure STL / 3MF files
│       └── test.blend             # Blender scene used for the renders
├── 02_Software/                   # Firmware (coming soon)
└── docs/                          # Images and schematic PDF for this README

Roadmap

• Schematic
• PCB layout v0.1 (Ø70 mm)
• Enclosure design & renders
• Order and assemble the first prototype
• Hardware bring-up & validation
• Firmware: sensor readout, LED air-quality indication
• Home Assistant integration (ESPHome / MQTT)
• Hardware v1.0 release

Building one

[!WARNING] This project is work in progress. Hardware v0.1 has not been manufactured and tested yet, so order boards at your own risk.

1. Open 01_Hardware/02_KiCad/air-quality-sensor/air-quality-sensor.kicad_pro in KiCad 10.
2. The fabrication files (Gerbers, BOM, CPL) for JLCPCB are in production/.
3. Print the enclosure from 01_Hardware/03_3D_Model/3D-Printing/.

License

Hardware (schematics, PCB, enclosure, renders): CC BY-NC-SA 4.0. You may build, study and modify this design for non-commercial purposes, as long as you credit the author and share your changes under the same license. Selling boards, kits or devices based on this design is not allowed without the author's written permission.

Firmware (02_Software/): GPL-3.0.

For commercial licensing, please get in touch.