For years, if you wanted to set up a serious APRS (Automatic Packet Reporting System) node—be it an iGate, a Digipeater, or a Tracker—you usually had two choices. You could buy an expensive, proprietary TNC (Terminal Node Controller), or you could wrestle with a soundcard modem and a dedicated PC.

But the game has changed.

Today, we are diving deep into a project that is making waves in the community, developed by Thai amateur radio operator Somkiat Nakhonthai (HS5TQA). It is called ESP32APRS_Audio, and it might just be the most versatile, cost-effective APRS solution available today.

What is ESP32APRS_Audio?

At its core, ESP32APRS_Audio is a firmware that turns a standard ESP32 microcontroller into a fully functional Software TNC.

Unlike other ESP32 projects that require specific LoRa modules or complex digital interfaces, this project utilizes the ESP32’s internal DAC (Digital to Analog Converter) and ADC (Analog to Digital Converter) to generate AFSK (Audio Frequency Shift Keying) tones directly.

In plain English: You can plug this $5 chip directly into the microphone and speaker jack of any analog radio—from a Baofeng UV-5R to a 25-year-old Yaesu mobile—and turn it into a modern, internet-connected APRS station.

Why This Project is a Game Changer

1. It’s a True “Soft-Modem”

Most modern APRS projects rely on external hardware modems. HS5TQA’s code implements the modem entirely in software.

• VHF: Standard 1200bps AFSK (Bell 202) for 2m operations.
• HF: 300bps AFSK (Bell 103) for long-range HF packet.
• UHF High Speed: 9600bps GFSK (supported on ESP32-S3).

2. The “Swiss Army Knife” of Modes

One firmware flash gives you every mode you could possibly need. You don’t need different code for different jobs; you just change the settings in the web interface.

• iGate (Internet Gateway): Listens to RF traffic and pipes it to the APRS-IS internet servers via WiFi.
• Digipeater: Listens for packets and re-transmits them to extend network range.
• Tracker: Connects to a GPS and beacons your location.
• Weather Station: Interfaces with weather sensors to report telemetry.

3. FX.25 Support

This is a huge technical win. The firmware supports FX.25, which is an upgrade to the standard AX.25 protocol. It wraps the standard packet in “Forward Error Correction” (FEC) data.

• The Benefit: If a packet gets slightly corrupted by static, FX.25 can mathematically repair it.
• Compatibility: It is fully backward compatible. Standard TNCs will just see a normal packet, but FX.25-enabled stations (like Direwolf or this ESP32) will enjoy much better decoding in noisy environments.

The Hardware: Simplicity Itself

You don’t need a degree in electrical engineering to build the interface. The repository provides the schematic for the ESP32DR Simple Circuit.

To connect the ESP32 to a radio, you essentially need three things:

1. Isolation: A simple 600:600 Ohm audio transformer prevents ground loops (hum) between your radio power and ESP32 power.
2. Level Adjustment: A voltage divider (potentiometer) to drop the radio’s loud speaker audio down to the 3.3V range the ESP32 can handle.
3. PTT Control: A simple NPN transistor (like a 2N3904) to trigger the Push-To-Talk on the radio.

Supported Boards:

• Standard ESP32 (DevKit V1)
• ESP32-C3
• ESP32-S3

The Software Experience: No Coding Required

One of the biggest barriers to entry for Ham projects is the “Compile Error.” You download a project, try to upload it, and spend 4 hours debugging library conflicts.

ESP32APRS_Audio solves this by focusing on a Web-Based User Interface.

1. Flash Once: You use the Espressif download tool to flash the binary files one time.
2. Config via WiFi: The ESP32 creates a WiFi Hotspot (ESP32APRS_Audio). You connect to it with your phone or laptop.
3. Browser Control: You navigate to 192.168.4.1 and are greeted with a full dashboard. You can set your Callsign, SSID, Latitude/Longitude, Digipeat paths, and Volume levels visually.

Advanced Features for the Power User

For those who want to push the envelope, HS5TQA has packed in enterprise-level features:

• VPN (WireGuard): Secure your connection if you are placing this on a remote mountain top.
• MQTT: Integrate your radio data into Home Assistant or other IoT dashboards.
• Bluetooth TNC: It enables the Bluetooth SPP (Serial Port Profile). You can pair your Android phone running APRSdroid to the ESP32, using it as a wireless TNC for your mobile operations.

How to Get Started

1. Visit the Repo: Go to GitHub – nakhonthai/ESP32APRS_Audio.
2. Order the BOM: An ESP32 DevKit, a few resistors, capacitors, and an RJ11 or TRRS jack for your radio.
3. Build the Cable: Follow the “ESP32DR Simple” schematic.
4. Flash & Deploy: Get your station on the air for under $20 USD.

Conclusion

The ESP32APRS_Audio project is a testament to the spirit of amateur radio. It takes accessible, inexpensive modern technology and bridges it with the legacy RF hardware we all love. Whether you are looking to fill a coverage gap in your area with a cheap Digipeater or build the ultimate mobile tracker, this project deserves a spot on your workbench.

https://github.com/nakhonthai/ESP32APRS_Audio