A Repeater Monitoring System using PLC Computers (Ongoing)

 

 

Every year, our small-town amateur radio club volunteers for the local Fourth of July parade. We coordinate floats, manage logistics, and keep everyone connected using 2-meter radios. At the heart of that communication is something most people never see: a repeater, a system that listens for weak radio signals and rebroadcasts them so they can travel much farther than a handheld radio ever could.

 

 

In 2025, that system almost let us down.

Cloud cover rolled in and lingered over the mountain where our repeater lives, slowly starving its solar panels of power. As battery voltage dipped, the repeater began cutting out at the worst possible time. Unfortunately, “just go check it” isn’t an option when the equipment sits on a mountaintop hours away. By the time we realized what was happening, we were already reacting instead of planning.

That moment planted a simple but important question: what if we could monitor the repeater remotely, before it fails?

Because this repeater also serves as a backup communication asset for Ventura County, reliability isn’t optional. The core monitoring system is built around industrial process logic controllers (PLCs)—hardware designed to survive extreme temperature swings, electrical noise, and long duty cycles. All components are RoHS-compliant and selected with the assumption that they may be ignored for months at a time… and still need to work.

Alongside the industrial hardware, an Arduino Uno with a LAN/SD shield handles local data logging. It records voltages, environmental conditions, and system states so that even if the network goes down, the data isn’t lost.

For non-critical tasks, a different approach makes more sense. An Arduino Uno Q, a Linux-based micro-controller with significantly more processing power, is used for higher-level functions like handling webcam data and pushing media to the cloud. If it fails, the repeater still works—but if it succeeds, we gain visibility we’ve never had before.

 

Everything ties together over Ethernet, connected through an industrial network switch. From there, data exits the site through a mesh network node—a decentralized network of transceivers that can reroute traffic dynamically if a link goes down. It’s slower than fiber and less glamorous than cellular, but in emergency scenarios, it’s resilient—and that’s what matters.

Once off the mountain, data is sent to both Arduino Cloud and Cloudflare R2. Redundancy is intentional. Arduino Cloud stores lightweight telemetry and logs, while Cloudflare R2 hosts larger data streams. A Cloudflare Pages site, backed by a Worker, pulls everything together into a single web interface where operators can see system status in real time.  If one service goes down, the other keeps running.

 

Now, yes, it’s a lot. That’s why I built a flowchart to show how everything connects and where each system fits into the bigger picture.

 

With the communication architecture finalized, I’ve moved into CAD modeling and enclosure design. Device-to-device protocols are actively being tested, and the system is slowly transitioning from “idea” to “something that can live on a mountain.”  Stay tuned for more updates!