Recipe: closed-loop hydroponic doser

Problem statement

A hydroponic reservoir (DWC, NFT, ebb-and-flow) needs:

• pH held in 5.5–6.5 range
• EC held at the crop’s setpoint (typically 1.2–2.4 mS/cm depending on crop and stage)
• Logged continuously
• Auto-corrections without human intervention for at least 7 days at a time
• No catastrophic over-dose if a sensor or pump fails

Architecture (split control + observability)

[Arduino Uno — deterministic control MCU]
  pH probe (via Atlas signal-conditioning)        4× peristaltic pumps
  EC probe (via Atlas signal-conditioning)  ───►   pH-up · pH-down · A · B
  temperature probe (DS18B20, for compensation)    via L298N driver
       │
       │ Serial bridge (UART)
       ▼
[ESP32 — observability node]
  publishes pH, EC, temp, last dose volume, dose-count, error states via MQTT
       │
       ▼
[Home Assistant on Raspberry Pi]
  dashboard, history, alerts

The Arduino runs a pure control loop:

1. Read pH, EC, temperature.
2. Apply temperature compensation to EC.
3. If pH out of range, dose 1 mL of pH-up or pH-down. Wait 5 min. Re-read. Repeat up to N times per hour (anti-runaway).
4. If EC below setpoint, dose 2 mL of nutrient-A and 2 mL of nutrient-B together. Wait 10 min. Re-read.
5. Send state to ESP32 over UART.

The ESP32 only publishes — it never directly drives a pump. This isolates the safety-critical dosing logic from the WiFi-stack instability domain.

Anti-runaway constraints

• Max doses per hour per chemical (e.g. pH-up: 5 doses/hour cap)
• Total dose-volume cap per day per chemical (alert and refuse to dose past it)
• Sensor-out-of-range triggers stop-doser — better to let the reservoir drift than to dose blindly into a broken-sensor reading
• Watchdog reset if the Arduino main loop stalls

Sourcing notes

• pH probes are consumables; budget replacement every 12–24 months
• Atlas Scientific signal-conditioning circuits are worth the cost over generic — orders-of-magnitude better noise floor
• Mark each pump line clearly; mixing nutrient-A into the pH-down line ruins the reservoir

Cost

• [[arduino-uno|Arduino Uno]]: $25
• ESP32: $10
• Atlas Scientific pH + EC kits: $200
• 4× peristaltic pumps + driver: $80
• Reservoir, lines, tank fittings: $50
• Total: ~$365

See also

Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.

• Combines: [[arduino-uno]] · [[esp32]] · [[ph-sensor]] · [[ec-tds-sensor]] · [[peristaltic-pump]] · [[mqtt]] · [[home-assistant]]