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.

Why E77-900M22S for MAV link Long Range?

Feature Benefit Integrated MCU + LoRaAll-in-one chip reduces component count and wiring868–930 MHz ISM bandLong range (up to 5.6 km line-of-sight)AT Command UARTEasy to interface with flight controllers or host MCUsUltra-low power sleep modeIdeal for airborne or solar-powered systemsCompact 14 × 20 mm sizeSuits small drone builds and remote sensors

E77-900M22S Feature

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

conne

Lora

LoRa (short for Long Range Radio) is a type of Low-Power Wide-Area Network (LPWAN) communication technology. It is designed for long-distance wireless transmission with minimal power consumption and low operational cost. The technology is primarily developed and promoted by the international company Semtech. LoRa operates in unlicensed ISM frequency bands worldwide, including 433 MHz, 470 MHz, 868 MHz, and 915 MHz, making it suitable for a wide range of global applications.

LoRaWAN

The LoRa Alliance is a global, non-profit organization established in March 2015 under the leadership of Semtech. It introduced the LoRaWAN protocol, a low-power wide-area network (LPWAN) standard based on an open-source MAC layer.

Network Architecture:

Topology: Star network

Components:

LoRa nodes/modules

Gateways or base stations

Network server, which includes:

Network control

Application server

Device Classes in LoRaWAN:

LoRaWAN defines three types of end devices based on their receive/transmit behavior:

???? Class A – Basic Bidirectional Devices

Opens two short receive windows after each uplink transmission.

Uses ALOHA-like protocol with randomized time slots.

Most power-efficient, ideal for battery-powered devices.

The server can only send downlink messages immediately after the device’s uplink.

???? Class B – Scheduled Receive Windows

Inherits Class A features but adds scheduled receive slots.

Devices sync with gateway beacons to open receive windows at predefined times.

Allows the server to predictably send downlink messages.

???? Class C – Continuous Reception

Keeps the receive window open nearly all the time, closing it only during transmission.

Consumes more power, but provides minimal downlink latency from server to device.

Note: The E77-400M22S and E77-900M22S modules support Class A and Class C operation modes.

Use Cases

Smart agriculture & irrigation

Environmental monitoring

Industrial automation

Remote metering (gas/water/electric)

Drone telemetry

Smart cities

Schematic Diagram

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

PCB Files

3D Files

Conclusion

In conclusion, this project presents a robust and efficient dual-band telemetry communication system built around the E77-900M22S and E28-2G4M27S LoRa modules. It is specifically designed to support long-range, low-power wireless data transmission, making it highly suitable for applications like MAVLink-based drone telemetry, remote sensing, or IoT deployments. The integration of both sub-GHz and 2.4 GHz bands offers flexibility—balancing range and data rate—while onboard UART, SPI, and SWD interfaces ensure easy development, debugging, and system integration. Overall, the design demonstrates a scalable and adaptable solution for reliable, real-time communication in embedded wireless systems.

For Full Project :

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