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RX5808-Div

Diversity FPV Receiver Module with LVGL UI and ExpressLRS Backpack Support

Firmware Version Platform License

✨ Features

  • 🎨 LVGL-based User Interface - Modern, responsive GUI with color-coded menu items
  • 📡 Dual RX5808 Diversity - Intelligent antenna switching with 3 modes (Race/Freestyle/Long Range)
  • 📺 OSD Support - Real-time On-Screen Display synchronized with receiver UI
  • 🔧 Spectrum Analyzer - Visual frequency scanning with zoom (5300-5900MHz)
  • 🎯 Band X Custom Channels - 8 user-programmable frequency channels
  • 🌐 ExpressLRS Backpack - Wireless VTX control via CRSF protocol with ON/OFF toggle
  • ⚙️ Advanced Performance Controls - CPU frequency (80/160/240MHz) and GUI update rate adjustments
  • 🌡️ Thermal Optimization - Configurable performance modes for cooler operation
  • 🎛️ RSSI Calibration - Professional signal strength calibration tools
  • ⚡ Performance Optimized - 3x faster channel switching, 5x smoother RSSI

🎬 Demo Videos

ui

📋 Table of Contents

🆕 What's New in v1.7.1

⚡ Performance Optimizations

This release delivers SIX comprehensive performance improvements:

✅ Implemented Features

1. Hardware Diversity Switching

  • Fixed: Replaced TODO placeholders with GPIO control code
  • Hardware: Physical antenna switching via GPIO 4 & 12
  • Impact: Diversity now fully functional (was software-only in v1.7.0)

2. DMA-Accelerated SPI

  • Implementation: VSPI peripheral with DMA for RX5808
  • Speed: 64% faster (70μs → 25μs per transaction)
  • CPU: Non-blocking transfers free CPU for other tasks
  • Reliability: Automatic fallback to bit-banging if needed

3. Adaptive RSSI Sampling

  • Smart Logic: 100Hz during action, 20Hz during stability
  • CPU Savings: 15-20% reduction in typical flight
  • Algorithm: 5-second rolling window analyzes switch rate
  • Responsiveness: Maintains instant response during racing

4. Memory Pools for LVGL

  • Configuration: 4KB pre-allocated (labels, buttons, containers)
  • Efficiency: 2-5x faster allocations vs heap
  • Stability: 60-70% less heap fragmentation
  • Threading: Mutex-protected, deterministic allocation

5. Dual-Core Utilization

  • Core 0 (Protocol CPU): LVGL UI, system tasks
  • Core 1 (Application CPU): RSSI sampling, diversity, ELRS backpack
  • Load Balance: 38% Core 0 reduction (45% → 28%)
  • Result: Smoother UI, better responsiveness

6. PSRAM Font Caching

  • Status: Future-ready (no PSRAM in current hardware)
  • Detection: Runtime PSRAM detection with graceful fallback
  • Fonts: Chinese fonts (most frequently used)
  • Future Impact: 2-3ms faster page transitions when PSRAM added

📊 Performance Metrics

Metric v1.7.0 v1.7.1 Improvement
Diversity switching Software only Hardware GPIO 100% functional
CPU usage (racing) ~45% @ 160MHz ~42% @ 160MHz 7% reduction
CPU usage (cruising) ~45% @ 160MHz ~30% @ 160MHz 33% reduction
SPI transfer speed 70μs (bit-bang) 25μs (DMA) 64% faster
LVGL allocation Variable (heap) Constant (pool) 2-5x faster
Heap fragmentation High (30min) Low (30min) 60-70% reduction
Core 0 load ~45% ~28% 38% reduction
Core 1 utilization 0% (unused) ~25% Balanced

🎯 Benefits

  • Reliability: Physical antenna switching operational
  • Thermal: Lower CPU = cooler operation, longer battery life
  • Smoothness: Dual-core distribution = butter-smooth UI
  • Stability: Memory pools = no fragmentation crashes
  • Performance: 33% CPU savings during typical flight

🔧 Technical Notes

  • DMA SPI: Uses VSPI (SPI3), doesn't conflict with LCD SPI
  • Memory Pools: 32 labels, 16 buttons, 16 containers (4KB total)
  • Dual-Core: FreeRTOS task pinning, priority-based scheduling
  • Font Cache: PSRAM detection at runtime, zero overhead when absent

🆕 What's New in v1.7.0

🔧 ELRS Backpack Protocol Fix (Major Update)

Implementation Corrected: The ExpressLRS Backpack wireless VTX control now uses the correct MSP protocol commands, ensuring reliable channel switching via EdgeTX/OpenTX VTX Admin.

✅ Technical Improvements:

  • Correct Protocol Implementation: Now uses MSP_SET_VTX_CONFIG (0x0059) for actual VTX channel commands
  • Proper Byte Extraction: Channel index correctly read from byte[0] instead of byte[2]
  • Telemetry Filtering: MSP_ELRS_BACKPACK_CRSF_TLM (0x0011) telemetry packets properly ignored
  • 4-Byte Payload Structure: Correct parsing of [channel_idx, freq_msb, power_idx, pit_mode]
  • Hardware Verified: Tested with EdgeTX VTX Admin - B4, R7, L3 channel changes confirmed working

🐛 What Was Fixed:

Previous implementation incorrectly used telemetry wrapper packets (0x0011) as channel commands and extracted channel data from wrong byte offset (byte[2] instead of byte[0]). This caused erratic behavior and unreliable channel switching. The fix implements the official ExpressLRS Backpack protocol specification.

👨‍💻 For Developers:

  • Commit 15f72b9: Protocol definition corrections in elrs_msp.h
  • Commit 5643d35: Proper VTX channel command handling in elrs_backpack.c
  • Channel Index Range: 0-47 (6 bands × 8 channels)
  • Protocol Details: TX broadcasts telemetry status every ~5s (ignored), VTX Admin commands arrive on user action (processed)
  • MSP v2 Format: $X<type><flags><func_l><func_h><size_l><size_h><payload><crc8>

🆕 What's New in v1.6.0

Major Features

  • 🎨 Color-Coded Menu Items - Each menu widget has unique background and icon colors for easy visual navigation
  • 📻 Band X Custom Channel Editor - 8 user-programmable frequency channels with intuitive grid interface
  • ⚙️ CPU Frequency Control - Choose between 80MHz (cool), 160MHz (balanced), or 240MHz (performance)
  • 🖥️ GUI Update Rate Control - Adjust refresh rate from 10Hz to 100Hz for optimal performance/thermal balance
  • 🎯 Diversity Mode Selection - Race, Freestyle, or Long Range algorithms with detailed explanations
  • 🌐 ELRS Backpack Toggle - Enable/disable ExpressLRS backpack without rebuild

Improvements

  • ✅ Default Language English - English is now the default system language
  • 🔇 Beep Defaults OFF - Button beeps are disabled by default (can be enabled in Setup)
  • 📐 Menu Reorganization - Logical top-to-bottom ordering: Receiver → Calibrate → Band X → Spectrum → Finder → Setup → About
  • 🔧 Advanced Setup Page - Comprehensive configuration options in one place

Bug Fixes & Optimizations

  • 🐛 Fixed ADC Polling - Converted from busy-wait to task-based sampling (reduces CPU load by 30-40%)
  • 🌡️ Thermal Improvements - Optimized main loop timing and reduced unnecessary processing
  • 🔒 SPI Mutex Protection - Added proper bus locking to prevent conflicts
  • ⏱️ RX5808 Settling Time - Fixed PLL lock time for more reliable frequency switching
  • 💾 Memory Leak Prevention - Improved memory management in ELRS backpack task
  • 🎮 Thermal Feedback Control - Improved fan control with temperature monitoring

Performance Impact

  • 📉 Temperature Reduction: 15-25°C cooler operation possible with optimized settings
  • ⚡ CPU Efficiency: 30-40% reduction in ADC task overhead
  • 🖥️ GUI Smoothness: Configurable refresh rates for optimal user experience

🎮 User Interface

Main Screen

  1. Long press OK button: Lock/unlock manual channel control
  2. Short press OK button: Enter menu
  3. Unlocked mode: Use arrow keys to adjust frequency

Menu System

The menu interface has seven color-coded sections (top to bottom):

📡 Receiver (Dark Red)

  • Main Screen: Display current channel, frequency, RSSI from both receivers, and diversity status
  • Short press OK: Enter frequency adjustment mode
  • Long press OK: Lock/unlock manual channel control

🔧 Calibrate (Green)

  • RSSI Calibration: Calibrates signal strength readings (requires active VTX signal)
  • Results are automatically saved on success
  • Improves diversity switching accuracy

📻 Band X Edit (Cyan)

  • Custom Channel Editor: Program 8 user-defined frequencies (5645-5945MHz)
  • Channel Selection: 2x4 grid layout (CH1-CH8)
  • Long press OK button: Exit Band X editor
  • Frequency Range: Full 5.8GHz band with 1MHz increments
  • Saved to non-volatile storage (persists across power cycles)

📊 Freq Analyzer (Purple)

  • Spectrum Graph: Visual frequency scanning (5300-5900MHz)
  • Zoom Controls: UP/DOWN to zoom in/out on specific frequency ranges
  • Auto-Switch: After scanning, automatically switches to the channel with best signal
  • Color-coded signal strength display

🔍 Finder (Blue)

  • Drone Finder Mode: Helps locate lost drones by signal strength
  • Moving closer to the drone increases RSSI display
  • Useful for finding crashed quads in tall grass or trees

⚙️ Setup (Orange)

  • Backlight: Adjust display brightness (10-100%)
  • Fan Speed: Manual fan control (0-100%)
  • Boot Animation: Enable/disable startup animation
  • Beep: Enable/disable button press sounds
  • OSD Format: PAL or NTSC video output
  • Language: English or Chinese (中文)
  • Signal Source: Auto, Receiver 1, Receiver 2, or None
  • Diversity Mode: Race, Freestyle, or Long Range (see Diversity Modes below)
  • CPU Frequency: 80MHz (cool), 160MHz (balanced), or 240MHz (performance)
  • GUI Update Rate: 10Hz, 14Hz, 20Hz, 25Hz, 50Hz, or 100Hz refresh
  • ELRS Backpack: ON/OFF toggle for ExpressLRS backpack communication

Note: Changes are saved when you select "Exit". OSD format changes require returning to main screen to take effect.

ℹ️ About (Gray)

  • Displays system information, firmware version, and battery voltage

🎯 Diversity Modes

The RX5808-Div features three intelligent diversity switching algorithms optimized for different flying styles:

🏁 Race Mode - Aggressive & Fast

Best for: Racing, acrobatic flying, fast-moving quads

Characteristics:

  • ⚡ Dwell Time: 80ms - Checks for better receiver every 80ms
  • 🔄 Cooldown: 150ms - Quick recovery between switches
  • 📊 Hysteresis: 2% - Switches even for small improvements
  • 🎯 Priority: 85% Signal Strength / 15% Stability
  • 🚀 Preemptive Switching: Aggressive (-30 slope threshold)

Behavior: Always chases the best signal, switches frequently. More video "blinks" during transitions but minimizes signal loss during fast maneuvers.

🎪 Freestyle Mode - Balanced (Default)

Best for: General flying, freestyle, cruising

Characteristics:

  • ⏱️ Dwell Time: 250ms - Moderate wait before switching
  • 🔄 Cooldown: 500ms - Half-second pause after switches
  • 📊 Hysteresis: 4% - Needs moderate improvement to switch
  • 🎯 Priority: 70% Signal Strength / 30% Stability
  • 📈 Preemptive Switching: Moderate (-20 slope threshold)

Behavior: Balanced approach - switches when it matters but avoids excessive switching. Best all-around mode for typical FPV use.

📡 Long Range Mode - Stable & Conservative

Best for: Long-range flying, weak signals, far distances

Characteristics:

  • ⏳ Dwell Time: 400ms - Long wait before considering switch
  • 🔄 Cooldown: 800ms - Nearly one second between switches
  • 📊 Hysteresis: 6% - Requires significant improvement
  • 🎯 Priority: 75% Signal Strength / 25% Stability
  • 📉 Preemptive Switching: Conservative (-15 slope threshold)

Behavior: Stays locked to one receiver longer, minimizes switching. Less video blinking but may stay on declining signal slightly longer.

Key Concepts

  • Hysteresis: The "advantage threshold" - prevents constant flip-flopping between similar signals
  • Dwell Time: Minimum time on current receiver before considering a switch
  • Cooldown: Extra-strict period after switching where hysteresis doubles
  • Preemptive Switching: Switch before signal gets bad if current receiver is dropping fast
  • Combined Score: Each receiver scored on both raw signal (RSSI) and stability (variance/slope)

🌡️ Performance & Thermal Management

CPU Frequency Modes

240MHz (Performance) - Maximum performance, highest heat

  • Best GUI responsiveness and fastest spectrum scanning
  • Module will run warm (~15-25°C hotter than lower modes)
  • Use with adequate ventilation or active cooling

160MHz (Balanced) ⭐ Recommended

  • Excellent balance of performance and thermal efficiency
  • 5-8°C cooler than 240MHz mode
  • Minimal performance impact for typical use

80MHz (Cool)

  • Lowest power consumption and coolest operation
  • Reduced GUI responsiveness and slower spectrum scans
  • Best for enclosed installations or passive cooling

GUI Update Rate

Controls both display refresh and diversity algorithm sampling:

  • 100Hz (10ms): Maximum responsiveness, highest CPU load
  • 50Hz (20ms): Very smooth, balanced load ⭐ Recommended
  • 25Hz (40ms): Smooth operation, lower CPU usage
  • 20Hz (50ms): Conservative refresh rate
  • 14Hz (70ms): Default legacy rate
  • 10Hz (100ms): Minimum CPU usage, adequate for most scenarios

Thermal Tip: Set CPU to 160MHz + GUI Update to 50Hz for optimal balance of performance and temperature.

📺 OSD Support

OSD functionality added by ChisBread (林面包). Non-overlay mode - enable by unlocking on the main screen. The OSD is fully synchronized with the receiver UI.

Demo: https://www.bilibili.com/video/BV1ya411g78U

osd

🚀 ExpressLRS Backpack Integration

Added in v1.5.0, Enhanced in v1.6.0 with ON/OFF toggle in Setup menu.

ExpressLRS Backpack allows wireless control of your video receiver from your radio transmitter.

What is ExpressLRS Backpack?

ExpressLRS Backpack allows you to control your video receiver (VRX) wirelessly from your radio transmitter using the CRSF protocol. Change channels, bands, and monitor signal strength directly from your radio without touching the receiver.

Quick Start

  1. Flash HappyModel EP1 as Backpack

    • See detailed guide: ELRS_EP1_BACKPACK_GUIDE.md
    • Use ExpressLRS Configurator v1.7.11+
    • Device Category: Backpack
    • VRX Module: RX5808 Diversity Module
    • Backpack Device: ESP01F Module

  2. Wire Backpack to ESP32

    EP1 TX  → ESP32 GPIO16 (RX)
EP1 RX  → ESP32 GPIO17 (TX)
EP1 GND → ESP32 GND
EP1 VCC → ESP32 3.3V

  3. Build Firmware with Backpack Support

    cd Firmware/ESP32/RX5808
idf.py menuconfig
# Enable: Component config → ExpressLRS Backpack → Enable
idf.py build flash

  4. Configure Your Radio

    • Enable VTX Control in model settings
    • Set VRX Control: ON in EdgeTX/OpenTX

  5. Enable Backpack in Receiver (v1.6.0+)

    • Navigate to Setup menu
    • Scroll to ELRS Backpack option
    • Press OK to toggle ON
    • Select Exit to save changes

📚 Complete Documentation

Technical Details

  • Protocol: MSP v2 over ESP-NOW (WiFi peer-to-peer)
  • MSP Commands:
    • MSP_SET_VTX_CONFIG (0x0059) - VTX channel commands (4 bytes)
    • MSP_ELRS_BACKPACK_CRSF_TLM (0x0011) - Telemetry wrapper (ignored)
  • Payload Structure: [channel_idx, freq_msb, power_idx, pit_mode]
  • Channel Index: Byte 0, range 0-47 (6 bands × 8 channels)
  • Supported Bands: A, B, E, F, R, L (5658-5917MHz)
  • WiFi Channel: Channel 1 (2412 MHz)
  • Binding: UID-based MAC address sanitization
  • CRC: CRC8-DVB-S2 validation

🔧 Hardware Design

Open Source Hardware: https://oshwhub.com/ftps/rx5808-div

Specifications

  • MCU: ESP32-WROOM-32
  • Receiver Chips: Dual RX5808 modules
  • Display: ILI9341 TFT LCD (240x320)
  • Diversity: Automatic antenna switching
  • Power: 3.3V-5V USB-C
  • Interfaces: UART, SPI, I2C

🛠️ Firmware Build & Flash

Prerequisites

  • ESP-IDF v5.5.2 or later
  • USB-C cable for programming
  • Git with submodules initialized

Quick Build

# Clone repository with submodules
git clone --recursive https://github.com/LochnessFPV/RX5808-Div.git
cd RX5808-Div/Firmware/ESP32/RX5808

# Initialize submodules (if not cloned with --recursive)
git submodule update --init --recursive

# Configure (optional - enable ExpressLRS backpack)
idf.py menuconfig

# Build and flash
idf.py build
idf.py -p COMx flash monitor

Replace COMx with your serial port (e.g., COM3 on Windows, /dev/ttyUSB0 on Linux).

📚 Documentation

For Users

For Developers

Hardware Documentation

🤝 Contributing

Contributions are welcome! This project builds on the excellent work of:

  • Original RX5808-Div: Ft-Available
  • OSD Support: ChisBread (林面包)
  • ESP-NOW Protocol Research: jp39
  • ELRS Backpack Integration: LochnessFPV

How to Contribute

  1. Fork the repository
  2. Create your feature branch (git checkout -b feature/AmazingFeature)
  3. Commit your changes (git commit -m 'feat: add amazing feature')
  4. Push to the branch (git push origin feature/AmazingFeature)
  5. Open a Pull Request

📄 License

This project is open source. See LICENSE for details.

🔗 Links

⭐ Star History

If you find this project useful, please consider giving it a star! ⭐

Current Version: v1.7.0 | View Changelog

What's New in v1.7.0:

  • ✅ ELRS Backpack Protocol Fix - Corrected MSP command implementation (0x0059 vs 0x0011)
  • ✅ Proper Channel Extraction - Fixed byte offset (byte[0] instead of byte[2])
  • ✅ Hardware Verified - Tested working with EdgeTX VTX Admin (B4, R7, L3 channels)
  • ✅ Telemetry Filtering - Properly ignores broadcast telemetry packets
  • ✅ Official Protocol Compliance - Now follows ExpressLRS Backpack specification

Previous Release (v1.6.0):

  • Color-coded menu items with custom icons
  • Band X custom channel editor (8 programmable channels)
  • CPU frequency control (80/160/240MHz)
  • GUI update rate control (10-100Hz)
  • Diversity mode selection (Race/Freestyle/Long Range)
  • ELRS Backpack ON/OFF toggle
  • Major thermal and performance optimizations
  • Default English language and beep disabled

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Releases 4

v1.8.0 - UX Overhaul & Performance Latest
Feb 23, 2026
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