Introduction

The MAVLink Long-Range System (mLRS) is an open-source, bidirectional telemetry link designed for UAVs, drones, and autonomous vehicles. It uses LoRa modulation to achieve robust, long-distance, low-bandwidth communication between a ground station and a vehicle using the MAVLink protocol.

The E77-900M22S module is based on the STM32WLE5CCU6, is an ideal core for this system because it combines:

• A Cortex-M4 MCU,
• A LoRa transceiver (sub-GHz),
• Ultra-low power consumption,
• Integrated UART and GPIO interfaces.

For full project :

https://electronicsworkshops.com/2025/06/14/mav-link-long-range-system-using-e77-900m22s/

Why E77-900M22S for MAV link Long Range?

Features

• Under ideal conditions, using transparent transmission protocol , the communication distance can reach 5.6 km;
• Under ideal conditions, using Lo Ra W AN standard firmware, the communication distance can reach 3.5 km;
• The maximum transmit power is 21.5dBm , multi-level software adjustable;

• E77-400M22S supports the global license-free ISM 433/470MHz frequency band;
• E77-900M22S supports the global license – free ISM 868/915 MHz frequency band;
• E77-400M22S supports Lo Ra W AN 1.0.3 EU433/CN470 standard;
• E77-900M22S supports Lo Ra W AN 1.0.4 EU868/US915/AU915/AS923/IN865/KR920/RU864 standard;
• E77-400/900M22S supports two device types: Class A and Class C;
• ~12SF spreading factors launched to support dense networks ;
• 1.8 ~ 3.6 V power supply, and any power supply greater than 3.3 V can ensure the best performance;
• External crystal uses 32.768KHz high precision industrial crystal and 32MHz high precision industrial active temperature compensation crystal;
• 14.0*20.0*2.7mm small size patch package, conducive to system integration development;
• Industrial grade standard design, supports long-term use at -40~+85℃;
• Optional dual antennas (IPEX/stamp hole) facilitate user secondary development and integration;

Recommended connection diagram

Use Cases

Smart agriculture & irrigation

Environmental monitoring

Industrial automation

Remote metering (gas/water/electric)

Drone telemetry

Smart cities

Schematic Diagram

This circuit diagram represents a dual-band long-range wireless communication system based on the Ebyte E77-900M22S (sub-GHz LoRa) and E28-2G4M27S (2.4 GHz) modules. The E77 module is the primary LoRa transceiver, connected to UART2 and SPI interfaces of a host microcontroller, and is powered by a regulated 3.3 V supply from an AMS1117 voltage regulator. It includes support for LEDs to indicate transmission, reception, and network status, along with a reset and bind button for configuration or firmware upgrade. The E28 module is controlled via SPI and provides a secondary communication link, possibly used for higher-speed short-range data. Debugging and programming access are available through SWD pins, and the overall system is designed for low-power, long-range telemetry applications such as MAVLink communication in drones or remote sensing.

PCB Files

3D Files

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Conclusion

In conclusion, this project presents a robust and efficient dual-band telemetry communication system built around the E77-900M22S and ...