Build Long-Range IoT Applications Fast With Meshtastic

Oh me, oh mesh! Many journalists in this business have at least one pet technology that’s never taken off in the way they think it should. Hypersonic passenger planes, deep-sea thermal-energy power plants, chording keyboards—all have their adherents, eager to jump at the chance of covering their infatuation. For me, it’s mesh radio systems, which first captivated me while I was zipping around downtown Las Vegas back in 2004. In that pre-smartphone, practically pre-3G era, I was testing a mesh network deployed by a local startup, downloading files at what was then a mind-boggling rate of 1.5 megabits per second in a moving car. Clearly, mesh and its ad hoc decentralized digital architecture were the future of wireless comms!

Alas, in the two decades since, mesh networking has been slow to displace conventional radio systems. It’s popped up on a small scale in things like theZigbee wireless protocol for the Internet of Things, and in recent years it’s become common to see Wi-Fi networks extended using mesh-based products such as the Eero. But it’s still a technology that I think has yet to fulfill its potential. So I’ve been excited to see the emergence of the open-source Meshtastic protocol, and the proliferation of maker-friendly hardware around it. I had to try it out myself.

Meshtastic is built on top of the increasingly popular LoRa (long-range) technology, which relies on spread-spectrum methods to send low-power, low-bandwidth signals over distances up to about 16 kilometers (in perfect conditions) using unlicensed radio bands. Precise frequencies vary by region, but they’re in the 863- to 928-megahertz range. You’re not going to use a Meshtastic network for 1.5-Mb/s downloads, or even voice communications. But you can use it to exchange text messages, location data, and the like in the absence of any other communications infrastructure.

The stand-alone communicator [bottom of illustration] can be ordered assembled, or you can build your own from open-source design files. The RAKwireless Meshtastic development board is based around plug-in modules, including the carrier board, an environmental sensor, I/O expander board, radio module, OLED screen, and LoRa and Bluetooth modules.James Provost

To test out text messaging, I bought three HelTXT handheld communicators for US $85 each on Tindie. These are essentially just a battery, keyboard, small screen, ESP32-based microcontroller, and a LoRa radio in a 3D-printed enclosure. My original plan was to coerce a couple of my fellow IEEESpectrum editors to spread out around Manhattan to get a sense of the range of the handhelds in a dense urban environment. By turning an intermediate device on and off, we would demonstrate the relaying of signals between handhelds that would otherwise be out of range of each other.

This plan was rendered moot within a few minutes of turning the handhelds on. A test “hello” transmission was greeted by an unexpected “hey.” The handhelds’ default setting is to operate on a public channel, and my test message had been received by somebody with a Meshtastic setup about 4 kilometers away, across the East River. Then I noticed my handheld had detected a bunch of other Meshtastic nodes, including one 5 km away at the southern tip of Manhattan. Clearly, range was not going to be an issue, even with a forest of skyscrapers blocking the horizon. Indeed, given the evident popularity of Meshtastic, it was going to be impossible to test the communicators in isolation! (Two Spectrum editors live in Minnesota, so I hope to persuade them to try the range tests with fewer Meshtastic users per square kilometer.)

I turned to my next test idea—exchanging real-time data and commands via the network. I bought a $25 WisBlock meshtastic starter kit from RAKwireless, which marries a LoRA radio/microcontroller and an expansion board. This board can accommodate a selection of cleverly designed and inexpensive plug-in hardware modules, including sensors and displays. The radio has both LoRa and Bluetooth antennas, and there’s a nice smartphone app that uses the Bluetooth connection to relay text messages through the radio and configure many settings. You can also configure the radios via a USB cable and a Python command-line-interface program.

In addition to basic things like establishing private encrypted channels, you can enable a number of software modules in the firmware. These modules are designed to accomplish common tasks, such as periodically reading and transmitting data from an attached environmental sensor plug-in. Probably the most useful software module is the serial module, which lets the Meshtastic hardware act as a gateway between the radio network and a second microcontroller running your own custom IoT application, communicating via a two- or three-wire connection.

The Meshtastic protocol has seen significant evolution. In the initial system, any node that heard a broadcast would rebroadcast it, leading to local congestion [top row]. But now, signal strength is used as a proxy for distance, with more-distant nodes broadcasting first. Nodes that hear a broadcast twice will not rebroadcast it, reducing congestion [bottom row].James Provost

For my demo, I wired up a button and an LED to an Adafruit Grand Central board running CircuitPython. (I chose this board because its 3.3-volt levels are compatible with the RAKwireless hardware.) I programmed the Grand Central to send an ASCII-encoded message to the RAKwireless radio over a serial connection when I pressed the button, and to illuminate the LED if it received an ASCII string containing the word “btn.”

On the radio side, I used a plug-in I/O expander to connect the serial transmit and receive wires. The tricky part was mapping the pin names as labeled on the adapter with the corresponding microcontroller pins. You need to know the microcontroller pins when setting up the receive and transmit pins with the serial module, as it doesn’t know how the adapter is set up. But after some paging through the documentation, I eventually found the mapping.

I pressed the button connected to my Grand Central microcontroller, and “button down” instantly popped up on my handheld communicators. Then I sent “btn,” and the LED lit up. Success! With that proof of concept done, pretty much anything else is doable as well.

Will makers building applications on top of Meshtastic lead to the mesh renaissance I’ve been waiting for? With more hands on deck, I hope to see some surprising uses emerge that will make the case for mesh better than any starry-eyed argument from me.