Project Overview
System Architecture
An Arduino Nano acts as a sensor hub, reading zone-level soil health data via RS485 multi-sensors and plant-level moisture data via capacitive sensors. The Nano reports to the FarmBot Raspberry Pi over USB serial. The Pi uses the data to trigger automated watering sequences and publishes all readings live to nahsfarmbot.org.
Soil Sensors
โ
Arduino Nano
โ
FarmBot Pi
USB Serial
USB Serial
โ
Auto Watering
REST API
REST API
โ
Web Dashboard
Flask
Flask
Sensor Tiers
Zone Sensors RS485 ยท 7-in-1
One per growing zone. Provides a full soil health picture for maintenance decisions and long-term trend monitoring.
- Moisture ยท Temperature ยท EC
- pH ยท Nitrogen ยท Phosphorus ยท Potassium
- Modbus RTU over RS485 via MAX485
- 12V DC โ powered from bed supply
- 120ฮฉ termination resistor at far end
Plant Sensors Capacitive
One per plant location. Measures soil moisture only. Drives individual automated watering decisions via FarmBot REST API.
- Analog moisture reading per plant
- Mapped to FarmBot XY coordinates
- Calibrated dry/wet threshold per soil type
- Up to 6 sensors per Arduino Nano (A0โA5)
- Expand with second Nano for more plants
Bill of Materials
Component
Qty
Purpose
RS485 7-in-1 Soil SensorALOUTSNOC TH-EC-PH-NPK โ amazon.com/dp/B0CXLHMYZX
2
Zone soil health โ moisture, temp, EC, pH, NPK
Capacitive Soil Moisture SensorsAITRIP 10-pack โ amazon.com/dp/B094J8XD83
1 pack
Plant-level moisture โ 8โ12 plants + spares
MAX485 TTL to RS485 ModulesDORHEA 12-pack โ amazon.com/dp/B094MKRTRC
1 pack
RS485 interface for Nano โ use 2, 10 spares
Arduino Nano
1
Sensor hub โ already on hand
Cat5 Cable
As needed
Sensor wiring loom โ already on hand
12V Power Supply
1
Zone sensor power โ already at bed
Weatherproof Enclosure
1
Houses Nano + MAX485 โ 3D printed at school
โ Wiring Notes
- Cat5 cable used as sensor loom โ 4 twisted pairs, 8 conductors total.
- RS485 zone sensors use one twisted pair per sensor (A/B differential) + one pair for 12V/GND.
- Capacitive sensors use 3 conductors each (VCC, GND, Signal) routed along remaining Cat5 pairs.
- Add 120ฮฉ resistor between A and B lines at the far end for runs over 1 meter.
- Zone sensors require 12V DC โ share GND with Nano but power separately from bed 12V supply.
- Use outdoor-rated Cat5 if possible โ indoor jacket degrades in sunlight and moisture.
- Nano powered via USB from FarmBot Pi.
Build Phases
1
Single capacitive sensor read
Nano reads one capacitive sensor and prints to Serial Monitor โ basic analog read confirmed.
2
Multi-sensor JSON output
Nano reads all capacitive sensors and formats labeled JSON output โ multi-sensor read working.
3
RS485 zone sensor via Modbus
Nano reads RS485 zone sensor through MAX485 module using Modbus RTU protocol via ModbusMaster library.
4
Pi reads Nano over serial
Python script on FarmBot Pi requests and parses all sensor readings from Nano via USB serial.
5
Automated watering
Pi compares readings to calibrated thresholds and triggers FarmBot watering sequences via REST API, moving to saved XY coordinates per plant.
6
Live web dashboard
Flask endpoints added to nahsfarmbot.org โ live moisture per plant, zone NPK/pH/EC readings, and watering history displayed on a public dashboard.
Calibration Notes
- Insert sensor in completely dry soil โ record raw value as DRY baseline.
- Water thoroughly, wait for drainage โ record raw value as WET baseline.
- Set watering trigger threshold at approximately 40โ50% between dry and wet values.
- Allow 1โ5 minutes for sensor to stabilize after insertion or soil disturbance.
- Recalibrate if soil composition changes significantly.
- RS485 NPK readings are relative reference only โ use for trend monitoring, not precise nutrient calculation.
3D Printed Enclosure
The junction box housing the Nano and MAX485 modules is a good candidate for the school 3D printer. Design it to mount cleanly on the FarmBot bed frame with neat cable management.
๐ฉ Mounting bosses for Nano + 2x MAX485
๐ Strain relief holes for Cat5 jacket
๐ป Cutout for USB cable to Pi
๐ Lid with overlap lip for moisture resistance
๐ Mounting tabs for bed frame attachment
๐ Cable management channel along frame