📡 FlexPilot ESP32 Antenna Switch - Modernize any antenna switch where you can replace switching with relays
WiFi + MQTT + Web Dashboard | Compatible With FlexRadio / FlexPilot Automation
This project implements a network-controlled antenna switch using an ESP32, ULN2803A transistor driver, and SIP reed relays.
It integrates perfectly with:
FlexPilot Node-RED Home Assistant
Any MQTT automation system
The firmware provides:
✔ Web-based control panel
✔ MQTT command/state topics
✔ Stable relay control (no auto-revert)
✔ Safe “Hold Last State” logic
✔ mDNS discovery
✔ Designed for silent low-RF-loss switching
🔧 Features
🌐 Web Interface
Buttons for Antenna 1, Antenna 2, All Off
Auto-refreshing state
Works on mobile and desktop
📡 MQTT Integration
Control from FlexPilot
Retained state messages
Topics:
flexpilot/antennaSwitch/cmd
flexpilot/antennaSwitch/state
🧠 Safe Behavior
If WiFi or MQTT disconnect: ➡ Relays do NOT change ➡ ESP32 holds last known state ➡ Zero risk of switching during TX
🧲 Hardware-Optimized
Uses ULN2803A darlington array to drive relay coils
Drives 5V reed relays safely from ESP32 logic
Designed for external RF relay board switching
🛜 mDNS Support
Access via:
🖼️ Screenshot (placeholder)
You can add screenshot later:
🛠️ Hardware Required
ESP32 (ESP32-C3, ESP32-WROOM, etc.)
ULN2803A driver IC
Hailge SIP-1A05 5V reed relays
450–500 Ω coil resistance
5V buck converter (for coil power)
Shared GND between ESP32 and ULN2803A
🔌 Wiring Diagram (ASCII) SIP-1A05 Reed Relay (4-pin) Pin 1 – RF NO Pin 2 – Coil - Pin 3 – Coil + Pin 4 – RF COM
ULN2803A → ESP32 → Relays ESP32 GPIO16 ─── 1B (ULN input) 1C (ULN output) ─── Relay1 Coil -
ESP32 GPIO17 ─── 2B 2C ─── Relay2 Coil -
Power Relay Coil + ─── 5V ULN COM ─── 5V ULN GND ─── ESP32 GND
Important: ESP32 3.3V must not power the coils.
📦 Firmware Installation (PlatformIO)
Install PlatformIO
Create new project:
Board: ESP32 Dev Module (or esp32-c3-devkitc-02)
Framework: Arduino
Add dependency:
lib_deps = knolleary/PubSubClient
Upload src/main.cpp
🧪 MQTT Command Reference Command Topic flexpilot/antennaSwitch/cmd
Commands Payload Action 1 Select antenna 1 2 Select antenna 2 0 All off off All off State Topic flexpilot/antennaSwitch/state
Payload is:
1 2 off
State is retained to ensure persistence after reboot.
🌐 REST API Set antenna /set?ant=1 /set?ant=2 /set?ant=0
Get state /state
Returns JSON:
{"antenna": 1}
📡 mDNS Hostname
The device is reachable at:
📂 Structure /src/main.cpp /platformio.ini /README.md /docs/ui.png /docs/wiring.png
🚀 Future Enhancements
OTA firmware updates
4-relay version (4-position switch)
FlexRadio auto-band-switch logic
Integration with SWR sensors
Home Assistant auto-discovery
FlexPilot-native panel
Rule engine:
"If band = 40m → Antenna 2"
"If SWR > 3 → Fallback antenna"
🏆 License
MIT License