Building a Smart Fertigation System
A practical system design for controlled nutrient injection, flow measurement, pump control, and future automation.
Overview
This guide covers the design and implementation of a smart fertigation system suitable for small commercial greenhouse operations. The system integrates injector pumps, inline flow sensors, EC/pH monitoring, solenoid valve control, and a Raspberry Pi gateway for scheduling and automation.
System Architecture
The fertigation system operates on a simple loop:
- Schedule trigger — A cron-based scheduler on the Pi initiates a fertigation cycle
- Valve open — Zone solenoid valves open to pressurize the target irrigation line
- Injection start — Peristaltic injector pumps dose concentrated stock solution into the mainline
- Flow monitoring — Inline flow sensors track total volume delivered
- EC/pH sampling — Downstream sensors verify nutrient concentration and pH
- Cycle complete — Pumps stop, valves close, data is logged
Hardware Selection
Injector Pumps
For small greenhouse operations (under 1 acre), peristaltic dosing pumps offer the best balance of accuracy, chemical resistance, and cost. Key specifications:
- Flow rate: 0.5–5 L/min adjustable
- Tubing: Silicone or Norprene for chemical compatibility
- Drive: Stepper motor for precise volume control
- Interface: PWM speed control via Teensy/ESP32
Flow Sensors
Inline turbine flow sensors work well for irrigation monitoring. The YF-S201 is a common starting point, but consider upgrading to a brass-body sensor for longevity:
- Range: 1–30 L/min
- Output: Hall-effect pulse (frequency proportional to flow)
- Connection: 1/2” or 3/4” NPT
- Accuracy: ±5–10% (adequate for irrigation, not lab-grade)
EC/pH Probes
Analog probe modules from Atlas Scientific provide reliable readings with I2C or UART interfaces. Budget for calibration solutions and plan for probe replacement every 12–18 months in continuous-use applications.
Software Stack
The control software runs on a Raspberry Pi 4/5:
- OS: Raspberry Pi OS Lite (headless)
- Control service: Python with FastAPI for HTTP API and scheduling
- MQTT: Mosquitto broker for sensor telemetry
- Database: SQLite for local logging (upgrade to PostgreSQL for multi-zone systems)
- Dashboard: Lightweight web UI for monitoring and manual overrides
Wiring Considerations
- Use shielded cable for EC/pH probe connections to minimize noise
- Keep high-voltage relay wiring (solenoid valves, pump motors) physically separated from signal wiring
- Use DIN rail terminal blocks for clean, serviceable connections
- Label every wire — future you will thank present you
Cost Estimate
| Component | Approximate Cost |
|---|---|
| Raspberry Pi 5 + case + PSU | $80–100 |
| Peristaltic pump (x2) | $60–120 |
| Flow sensor (x2) | $15–30 |
| EC probe + interface | $80–120 |
| pH probe + interface | $80–120 |
| Solenoid valves (x4) | $60–100 |
| Relay board | $15–25 |
| Wiring, connectors, enclosure | $50–80 |
| Total | $440–695 |
Next Steps
- Set up the Raspberry Pi with the control service
- Wire the first zone with a single pump and flow sensor
- Implement basic scheduling with volume-based cutoff
- Add EC monitoring for closed-loop concentration control
This system is designed to grow incrementally. Start with one zone and manual stock mixing, then add automation as you validate each component.