Chlora 🌿

Chlora is an open-source, closed-loop domestic photobioreactor designed to purify indoor air, sequester $CO_2$, and produce oxygen. Fully replicable and 3D-printable, the system is automated via a Raspberry Pi 5 to bring industrial-grade bioreaction into the home.

The biological core of Chlora relies on the microalgae Chlorella vulgaris. With just 10 liters of culture, this compact system matches the daily photosynthetic efficiency of 1 to 2 medium-sized indoor trees.

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How It Works

1. Turbidity: The Pi 5 reads an optical turbidity probe over I2C. The probe is analog; an ADS1115 on bus 1 (address 0x48) is what the Pi actually talks to.
2. Filtration: A relay board on GPIO 17 switches the aquarium pump. The pump starts when turbidity crosses 280 NTU and stops below 90 NTU, so the relay does not chatter. A missing sensor forces the pump off.
3. Algae cycle: The same reading places the culture in lag, growth, peak, harvest, or recovery.
4. Oxygen: The panel reports oxygen production from turbidity and the 10 L culture. The yield is in firmware/chlora/config.py.
5. Screen: The touch display, or any HDMI panel, opens a local kiosk page with cycle phase, turbidity, filter controls, and oxygen production.

The 5 µm filter sits on the harvest line. The controller reads turbidity and drives the pump relay.

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Hardware & Components

• Brain: Raspberry Pi 5
• Screen: Raspberry Pi Touch Display 2 (DSI) or an HDMI display
• Culture: Chlorella vulgaris, 10 L
• Turbidity: analog optical probe, digitized by an ADS1115 on I2C
• Pump board: active-low relay module, GPIO 17, switching the pump's own supply
• Filter: 5 µm mesh on the harvest line

Wiring: electronics/README.md. Mechanical notes: hardware/README.md.

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Run

cd firmware
python3 -m chlora

The panel is at http://127.0.0.1:8080/. On the Pi 5 the same process owns the ADS1115 and the pump relay.

Install the system packages, enable I2C, and let the service own the GPIO:

sudo apt install python3-gpiozero python3-lgpio python3-smbus2 chromium
sudo mkdir -p /opt/chlora
sudo cp -a firmware display /opt/chlora/
sudo cp /opt/chlora/firmware/chlora.service /etc/systemd/system/chlora.service
sudo systemctl enable --now chlora.service

Edit User= in the unit if the login is not pi. The desktop session should autologin and launch firmware/kiosk.sh (see electronics/README.md).

cd firmware
python3 -m unittest discover -s tests -v

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Repository Structure

├── hardware/          # vessel, pump, filter, screen (mechanical notes)
├── electronics/       # Pi 5 pinout, ADS1115, relay board, kiosk
├── firmware/          # control loop, I2C turbidity, pump relay, tests
│   └── chlora/
│       ├── hardware/  # ADS1115 probe, pump relay, vessel balance
│       └── control/   # algae cycle, filter hysteresis, oxygen estimate
├── display/           # kiosk page served on the Pi screen
└── LICENSE            # MIT License