Deploying a Wireless Sensor Network at an 18th‑Century Gristmill

Monitoring century‑old industrial processes is challenging, but a network of nRF24L01 RF transmitters makes it safer, faster, and more reliable.

Story

Modern factories rely on digital monitoring to enhance safety, productivity, and ease of operation. In contrast, an 18th‑century gristmill—powered primarily by line shafts and wooden pulleys—still operates with minimal electricity. When tasked with designing a sensor network for this historic site, I saw an opportunity to blend heritage with cutting‑edge technology.

The mill functions as one large machine with numerous concurrent processes. To manage this complexity, we installed a variety of sensors that monitor grain levels, motor output, temperature, humidity, and, in future phases, grain flow and bearing temperatures. The resulting data stream eliminates the need for manual walk‑through inspections across the building’s four floors and supplies quantitative metrics for statistical analysis.

The network comprises standard Arduino‑powered nodes, a central base node, and a Raspberry Pi that serves as the server and data interpreter.

Hardware Overview

Each node uses an Arduino Nano paired with an nRF24L01 (RF24) module. The RF24 module can operate at 3.3 V for optimal performance; I added a 10 µF electrolytic capacitor close to its power pins to prevent sporadic power loss.

I designed a custom PCB that integrates the Arduino Nano, RF24 module, capacitor, two indicator LEDs, and a micro‑USB port. The assembled board is housed in a 3D‑printed case for easy wall or surface mounting.

To extend range beyond the standard 5–10 ft, I soldered a 7‑inch 18‑gauge wire onto the RF24’s antenna trace, achieving 20–30 ft. A generous amount of hot glue secures the antenna, preventing trace deformation.

Node and Base Programming

The RF24Network library (by Tmrh20) structures the mesh as a tree. Each node’s address is octal; a node can branch to no more than five children. For example, nodes 011 and 022 both branch from node 02. Repeater nodes (e.g., 01, 011, 0111, 01111) forward data, while sensor nodes (e.g., 03, 0211, 0311) generate measurements for the base node (00).

Both node and base programs share identical C structs for message payloads, ensuring seamless serialization and deserialization across the network.

Attaching Sensors to a Node

Grain Bin Sensing

Ultrasonic sensors positioned on the top of grain bins measure depth. Three sensors share a single trigger pin but use separate echo pins for clear timing isolation.

Temperature and Humidity Sensing

DHT11 modules provide temperature and humidity data throughout the building. Maintaining stable environmental conditions is critical for consistent flour fineness.

Read More Detail : Building a Sensor Network for an 18th Century Gristmill