Use HamMessenger to easily send text messages via Very High Frequency.
I first encountered radio communication when I was about five or six years old. My father was an electrician at the airport, and he often brought home a walkie-talkie, which my brothers and I would play with in the garden. This was my only experience with radio until a friend and I decided to get our amateur radio licenses. A few months after making that decision, the lockdowns due to the COVID-19 pandemic provided a great opportunity to learn about communication using amateur radio equipment.
However, I found that communicating solely with amateur radio equipment was a bit boring. Then I remembered a police radio signal scanner my father had, which occasionally emitted strange sounds like those from a dial-up modem. At that moment, I had a flash of inspiration and thought of HamMessenger. What if I could find a simple way to do digital communication using handheld radio equipment?
I began learning about the various models people use for digital communication with amateur radio equipment and stumbled upon the Automatic Packet Reporting System (APRS). APRS is a store-and-forward wireless networking protocol developed 25 years ago by U.S. Navy researcher Robert Bruninga for real-time tracking of tactical information. APRS operates in the 2-meter band of Very High Frequency (VHF) and is widely used in position beacons or weather stations. Now we can check APRS activity in our area via www.aprs.fi.
APRS supports sending text messages, and if you’re within range of an internet gateway node, you can even exchange SMS text messages with mobile phones and send emails containing a line of information. Traditionally, sending text involved connecting a personal computer to a Terminal Node Controller (TNC) packet radio modem and then connecting to the radio equipment (the signal transmitted as audio tones, just like an old dial-up modem). Recently, TNC modems that can interact with smartphones have emerged. These projects are amazing! However, the core of HamMessenger was influenced by my simple childhood experiences. I wanted to create a portable device that could connect to handheld radio equipment, which would be a standalone and complete device with a built-in keyboard, screen, and GPS receiver.
First, I needed to determine the hardware and software required. I found MicroAPRS, an open-source firmware package compatible with Arduino for DIY packet radio modems. With MicroAPRS, you can quickly build a fully functional APRS modem that can automatically switch between receiving and transmitting radio signals.
This is fantastic! Now I can focus on the remaining parts of HamMessenger. I had considered using a Raspberry Pi. That would be cool, but the Raspberry Pi is a bit overkill. The Raspberry Pi has high power requirements, and if it doesn’t perform a controlled shutdown, there is a risk of corrupting the file system, which can happen when the battery runs out.
So I decided to use a dual Arduino approach. One Arduino Pro Mini ($10) as the modem to run MicroAPRS and communicate with the rest of the system via serial connection; and one Arduino Mega 2560 ($40) as the central controller, connecting the modem, keyboard, display, and GPS. The system is powered by a rechargeable battery and a battery management board.
The GPS can provide location data, integrated into most APRS transmissions. I chose a NEO 6M GPS receiver ($10), which is popular among DIY drone enthusiasts. The NEO has a serial interface like my modem.
In my initial design, the manual input setup was very simple, with only three buttons. The first button enters the display menu and modifies parameters, the second button selects submenus or sets parameters, and the third button cancels parameter entry or navigates to the upper menu.
Finally, since using buttons to input text was too difficult, I replaced them with a CardKB QWERTY mini keyboard ($8.5). However, due to the limitations of the three-button system, I had to simplify the user interface of HamMessenger as much as possible. I am now very grateful for this, as it means that you can easily operate HamMessenger with basic APRS knowledge.
For the display, I chose an OLED screen because of its power efficiency. The only downside of amateur OLEDs is their small size. The most common is the 0.96-inch display, but I found a 1.3-inch display for $9 that can communicate via
I2C serial bus.
The final module component needed for HamMessenger is non-volatile memory to store received messages. I decided to use a micro SD card reader, as it is suitable for the SPI interface protocol.
All components are connected to the Arduino Mega. I chose the Mega as the central controller because it requires low power and has sufficient resources to manage multiple different module connections—two serial ports, two serial peripheral interfaces, and one
I2C connection. (Then I added a third serial port so it could be controlled by a personal computer or other devices based on an ASCII-coded API.)
I designed a shield using Autodesk’s Eagle (a printed circuit board that can accommodate these modules and some supporting circuits that plug directly into the top of the Mega), and then 3D printed a casing in Fusion 360 using the shield design files (details can be found on the HamMessenger page on GitHub).
Although HamMessenger is currently still in the prototype stage, it runs well. I installed a HamMessenger in my truck, also serving as a positioning beacon. Of course, it will never replace the mobile phones most people use, but it can be very useful in areas without signal coverage. Moreover, I primarily made it to enhance a type of electronic product, replacing the use of amateur radio equipment. If you need an easy way to learn and integrate these amateur hobbies, I think HamMessenger is a great way to do so.
Author: Dale Thomas
IEEE Spectrum
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