Tx rf

LoRa Telemetry Node

An end-to-end telemetry link that reads MAVLink 2 data from a Pixhawk over UART, packs it into a compact binary frame, encrypts it, and relays it over a long-range 868 MHz LoRa link to a ground station running QGroundControl.

[Pixhawk TELEM2] --UART MAVLink2--> [ESP32-S3 TX Node] --LoRa 868MHz--> [ESP32-S3 RX Node] --USB--> [QGroundControl]

The ESP32 does not read any sensors itself — Pixhawk is the only data source. The TX node parses MAVLink, serializes + encrypts a fixed-size packet, and transmits it over LoRa; the RX node decrypts and re-emits it as MAVLink 2 over USB so QGroundControl sees a normal telemetry stream.

LoRa Module

Both nodes use an EBYTE E22-900T30D (SX1262, 868 MHz, up to 30 dBm) LoRa transceiver module, talking to the ESP32 over UART in the module's Normal (transparent) mode.

Power warning: the E22-900T30D draws up to ~500 mA while transmitting. Do not power it from the ESP32's own 3.3 V regulator — use a dedicated AMS1117-3.3 LDO (1 A rated), with a shared ground between the ESP32 and the E22.

Bridge Mode + Air Data Rate

Each node can run in one of two modes, selected (along with the LoRa air data rate) from a web configuration panel rather than a physical switch:

• BRIDGE_TRANSPARENT — the node becomes a transparent UART bridge so Mission Planner can reach the Pixhawk directly through the LoRa link for parameter/calibration/waypoint work.
• BRIDGE_COMPRESSED — normal telemetry mode: TX parses → packs → encrypts → transmits; RX receives → decrypts → unpacks → re-emits MAVLink.

Holding the config button (GPIO9) for 3 seconds opens a WPA2-protected Wi-Fi access point (TUAV-TX-Config / TUAV-RX-Config) with a captive portal for selecting bridge mode, air rate, and Wi-Fi password. Changing the mode/rate from the RX node automatically re-synchronizes the TX node over the RF link itself — no need to configure both ends by hand. See CLAUDE.md for the full protocol details.

PCB

A complete KiCad 10 PCB design lives under hardware/pcb/, covering both nodes as a two-board stack:

• main — ESP32-S3-DevKitC-1 socket + power section (UBEC input → PTC fuse → reverse-polarity protection → a dedicated buck regulator that isolates the E22's transmit current pulses from the ESP32 rail). Identical design for both TX and RX; fabricate two copies.
• tx_rf / rx_rf — the E22-900T30D module plus node-specific connectors (TX: Pixhawk TELEM2 JST-GH; RX: SSD1306 OLED header), on a small board that plugs directly onto main via a 16-pin header/socket (J4), stacked so the assembly stays compact.

Each project folder includes the schematic, PCB layout, custom footprint/ symbol libraries, and ready-to-fabricate Gerber + drill files (gerbers/). Signal-net routing is left for completion in the KiCad GUI; net assignments are DRC-verified and the ratsnest will guide it.

Hardware Overview

Pin Mapping

TX Node (air)

RX Node (ground)

E22 M0=LOW, M1=LOW selects Normal TX/RX mode (set automatically at boot). The E22↔ESP32 UART baud follows the selected air data rate (see table above); the Pixhawk and ground-station links stay fixed at 57600 baud regardless of LoRa mode.

Packet Format (40 bytes, plaintext)

Encryption

Telemetry is encrypted with AES-128-CTR (ESP32 hardware AES accelerator via mbedTLS) before transmission: 40-byte plaintext → 40-byte ciphertext, plus an 8-byte nonce (seq_id + low bytes of millis()) sent alongside it. The key lives in common/aes_config.h as AES_KEY — the checked-in value is a placeholder, change it before any real deployment, and flash both nodes with the same key.

Separately, copy common/secrets.h.example to common/secrets.h and fill in your own WEB_CONFIG_SALT (generate one with openssl rand -hex 32). This salt authenticates the HMAC on the RX→TX mode/rate sync command over the RF link; secrets.h is gitignored and must never be committed.

Build & Flash

pip install platformio

# TX node
cd tx-node && pio run --target upload

# RX node
cd rx-node && pio run --target upload

QGroundControl Setup

Application Settings → Comm Links → Add:

• Type: Serial
• Port: the RX node's COM / ttyACM port
• Baud rate: 57600

See docs/qgc_setup.md for details and docs/breadboard_wiring.md for a breadboard wiring guide (or use the PCB design above instead).

License

MIT