Ingredient
Modbus / RS-485
Also known as: Modbus RTU, RS-485, Modbus TCP
Industrial serial communication protocol (Modbus) running over a differential-pair physical layer (RS-485) — the lingua franca of industrial control equipment, weather stations, soil-moisture probes, and commercial-grade farm sensors. RS-485 supports 32 devices on a single bus, runs at 9600–115200 baud, reaches up to 1200 meters (4000 ft) per segment. Modbus defines the message format on top: holding registers, input registers, coils, discrete inputs. The right ingredient when interfacing with industrial equipment that won't speak I²C or HTTP — most commercial weather stations, NPK-EC-pH soil probes, VFDs, and PLCs.
Inputs / outputs
- Physical: RS-485 differential pair (A, B), with optional ground reference
- Topology: linear bus, 32 devices per segment without repeaters
- Distance: up to 1200 m at 9600 baud; reduces with higher baud rates
- Speed: 9600, 19200, 38400, 57600, 115200 baud common
- Protocol: Modbus RTU (serial framing) or Modbus TCP (Ethernet wrapping)
Solves / unlocks
- Reading commercial weather stations (Davis Vantage Pro, Campbell Scientific)
- Industrial NPK / pH / EC / temperature soil probes (the proper agronomy-grade sensors)
- Variable-frequency drive (VFD) control for pump motors
- Long cable runs without repeaters or gateways
- Reading existing PLC infrastructure on legacy farm equipment
- Weighing scales and load cells
Constraints
- Polarity matters — A/B (or D+/D−) must be wired consistently across the bus.
- Termination resistors at each end of long buses (120 Ω); skipping these causes reflections.
- Bias resistors on the bus when no master is transmitting.
- One master, many slaves — Modbus is request/response; only the master initiates.
- Slow compared to modern IP protocols — high-frequency control is not Modbus’s job.
Source
- MAX485 transceiver: ubiquitous, ~$1 per IC
- Library (Arduino): https://github.com/4-20ma/ModbusMaster
- Python (Pi/server): https://github.com/pymodbus-dev/pymodbus
- Spec: https://modbus.org/specs.php (free)
See also
Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.
- Member of: [[ingredient]]
- Combines with: [[arduino-uno]] · [[esp32]] · [[raspberry-pi]] · [[node-red]] · [[home-assistant]]
What links here, and how
Inbound connections from across the wiki, grouped by lens and by relationship. These appear automatically — every entity page declares what it links to, and that data populates here on the targets.
Practical
contains
- Farm-tech toolkit comms / industrial serial protocol for commercial equipment
combines with
- Home Assistant HA Modbus integration ingests industrial sensor data into the home/farm automation graph
- Node-RED Node-RED Modbus nodes integrate industrial equipment into IoT flows
- NPK soil probe (RS-485) the probe speaks Modbus-RTU; the standard ingestion path
4 inbound links · 6 outbound