Mesh Network Radio Hardware
Hardware for "prepared civilians"
Mesh radio networks are an electronic network where the connection medium is radio.
For this article, we will take a look at the RAK wireless hardware (https://rakwireless.com/en-us). Hardware manufactured by other companies will be different but will provide the functional components required for a mesh radio network.
For the discussion below, refer to the above picture.
There is a base board. In the picture above, the base board is barely visible because it is mostly covered by several other modules. In other technologies, this board might be called a backplane or a mother board. It provides mounting and interconnection for all the modules that make up a mesh radio network transmitter/receiver (transceiver or radio). RAK calls their base board a “WisBlock Base board.” This base board can be used to build lots of different configurations of radios. One important thing to note is that the base board has the USB-C connection port.
The Meshtastic mesh radio network functionality is provided by the RAK4631 module. This module has the radio, and a computer module. In the RAK Wireless Meshtastic starter kit that I bought, this module came mounted to the WisBlock base board.
The radio module is a SEMTECH transceiver (SEMTECH SX1262). The radio is specifically designed for LoRa (Long Range) radio communications. The radio module provides connections between radios so that the computers can communicate. The radio connections replace the wires used in other networks.
The computer module is the brain of the mesh radio. It does the heavy lifting for the mesh radios that I built. The computer is a Nordic nRF52840.
( https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fkeyfeatures_html5.html )
The core of the computer module is a 32-bit ARM processor. The computer module has a built-in Bluetooth radio for wireless app connections to the computer. The computer module has 1 MB of flash memory and 256 kB of RAM. The module has power management functions, security functions, a temperature sensor, audio interfaces, a USB interface, and Near Field Communications (NFC). It is a full function computer that can be used for a lot of different purposes.
Combining the computer module with the SEMTECH radio, antennas, and software creates a mesh radio. For my build, I added a GPS module and receiver. The GPS module plugs into the WisBlock base board. The base board connects the GPS module to the computer module.
I added an 850 mAh (milliamp hour) battery and a blade antenna. Then I mounted it all inside a case with a solar panel. I bought the case from RAK Wireless along with the Meshtastic starter kit. There is a battery connector and a solar panel connector on the WisBlock base board. The computer module manages battery charging. The battery charges when the USB-C connector is connected to either a computer or a power block. It also charges from the solar panel. If you look closely, you can see that I had to re-wire my battery connector. The battery connector polarity was reversed from the board polarity. The simple fix was to switch (cut and reconnect) the wires to the correct polarity.
I also added an OLED display. The display is necessary for the first Bluetooth pairing. On the first Bluetooth pairing, the radio displays a security code for pairing. I turned off the security code and I’m working through whether I need the display. I think I will remove it before I deploy the packaged radio. Everything else is mounted securely but I could not figure out a secure and rugged mounting method for the display. After I turned off the Bluetooth pairing security code, I can get by without the display. I’m pondering adding a cable connection so that I can connect a display when needed and remove the display for normal operations.
I built three of these radios because one radio in a mesh network is not very useful. So far, I’ve only been able to test them in a tabletop setting. The next step is to take the radios out for some field testing. These radios are capable of communicating at quite long distances. The record is 254 Km[i].
There are a lot of Meshtastic nodes online. Using the iOS Meshtastic application, I can see eight nodes from my house near Greenville, SC. I see nodes online almost everywhere I go.
Of course, the hardware is inert without software. In the next article I’ll look at the Meshtastic software. That will be a few weeks away. I leave next week to walk the Camino Primitivo[ii] in Spain and I won’t be doing any radio testing during that walk.
[i] https://meshtastic.org/docs/introduction/
[ii] https://www.pilgrimagetraveler.com/camino-primitivo.html
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