Two Antennas, One Accurate Heading: Building a Dual GNSS Guidance System with W5500 and AgOpenGPS

Build a precision agriculture guidance system using ESP32, dual ZED-F9P GNSS receivers, and WIZnet W5500 Ethernet for accurate RTK heading and reliable AgOpenGP

COMPONENTS Hardware components

Espressif - ESP32S

x 1

WIZnet - W5500

x 1

PROJECT DESCRIPTION

Quick Facts

Item	Description
Category	Precision Agriculture
Platform	ESP32
Ethernet	WIZnet W5500
GNSS	Dual u-blox ZED-F9P
Communication	UDP, NTRIP
Software	AgOpenGPS
Difficulty	⭐⭐⭐⭐☆ Advanced
Primary Function	Absolute Heading Generation

Intuitive explanation

Modern precision agriculture depends on accurate vehicle heading as much as precise positioning. By combining two GNSS receivers, the system calculates the tractor's orientation even at low speeds or while stationary, enabling smooth automated steering. The W5500 provides reliable wired Ethernet communication with AgOpenGPS, ensuring stable delivery of RTK positioning and heading data. This approach is commonly used in autonomous tractors, precision farming equipment, field mapping, and other agricultural guidance systems where consistent navigation is essential.

Why This Project Matters

Most GNSS-based guidance systems estimate heading from vehicle movement.

That approach works while driving forward at speed, but becomes unreliable when the vehicle slows down, stops, or reverses. During these situations, steering accuracy decreases because the calculated heading no longer represents the vehicle's actual orientation.

A dual-antenna GNSS system eliminates this limitation by measuring the baseline between two antennas instead of estimating heading from motion.

The result is a stable heading that remains accurate even while stationary, allowing automatic steering systems to maintain reliable positioning throughout field operations.

Real-World Applications

This architecture is well suited for applications such as:

Precision agriculture guidance systems
Autonomous tractors
RTK-based field navigation
Agricultural robotics
Automated outdoor vehicles

System Overview

The ESP32 receives GNSS data from two ZED-F9P receivers, calculates the vehicle heading, and transmits navigation information to AgOpenGPS.

RTK Corrections
        │
        ▼
Dual ZED-F9P Receivers
        │
        ▼
ESP32 Heading Processor
        │
        ▼
W5500 Ethernet
        │
        ▼
AgOpenGPS
        │
        ▼
Auto Steering

Unlike conventional heading estimation, the vehicle orientation is calculated directly from the measured antenna baseline.

Where WIZnet Fits

The W5500 provides the project's wired Ethernet interface.

Rather than relying on Wi-Fi for continuous communication, the W5500 delivers deterministic Ethernet connectivity between the controller and AgOpenGPS.

Within this architecture, the W5500 is responsible for:

UDP communication
NTRIP data forwarding
AgIO discovery messages
Reliable Ethernet transport
DHCP or Static IP networking

Meanwhile, the ESP32 remains dedicated to GNSS parsing, heading calculation, and application logic.

Separating networking from navigation processing improves system reliability while simplifying software design.

Technical Highlights

Absolute Heading from Dual GNSS

Heading is computed from the relative position between two RTK GNSS receivers rather than vehicle movement.

Advantages include:

Accurate heading while stationary
Stable heading during turns
Reverse driving support
Reduced magnetic interference

Multiple Communication Modes

The firmware supports multiple transport methods, including:

USB
Ethernet (W5500)
Wi-Fi via router
Direct Wi-Fi

This allows the same navigation firmware to be deployed across different installation environments.

Robust Ethernet Communication

The Ethernet implementation includes:

Automatic DHCP with Static IP fallback
Link-status monitoring
Hardware detection
Multiple UDP channels
Automatic recovery after network failure

These features make the system suitable for outdoor operation where network interruptions may occur.

Practical Tips

Install both GNSS antennas symmetrically across the vehicle.
Maintain a rigid antenna baseline for accurate heading calculation.
Assign unique MAC addresses if multiple controllers share the same network.
Verify RTK corrections before testing steering performance.
Use wired Ethernet when maximum communication stability is required.

Difficulty

⭐⭐⭐⭐☆ Advanced

Recommended for developers with experience in:

ESP32 firmware
RTK GNSS
UDP networking
Precision agriculture
Embedded Ethernet

Similar WIZnet Maker Projects

Project	Focus	Difference
STM32 Modbus TCP Controller	Industrial Ethernet	Focuses on factory communication rather than navigation.
OpenPLC with W5500	Industrial Automation	PLC-based control instead of vehicle guidance.
MQTT Dashboard with W5500	IoT Monitoring	Cloud telemetry rather than real-time positioning.

FAQ

Why use two GNSS receivers?

A dual-antenna system calculates heading from the measured antenna baseline, providing accurate orientation even when the vehicle is stationary.

Why use W5500 instead of Wi-Fi?

W5500 provides stable wired Ethernet communication with hardware TCP/IP offloading, reducing communication variability during continuous field operation.

What role does the ESP32 play?

The ESP32 processes GNSS data, computes heading, manages communication, and interfaces with AgOpenGPS.

Can this system operate without Ethernet?

Yes. The firmware also supports USB and Wi-Fi communication, although Ethernet provides the most stable wired connection.

Who is this project suitable for?

It is intended for advanced makers, agricultural automation developers, and engineers building RTK guidance systems.

Source

Repository: https://github.com/Jeep1945/Dualheading-2022

Primary hardware:

ESP32
WIZnet W5500
u-blox ZED-F9P GNSS Receivers
AgOpenGPS

Wiznet makers