Ethernet Relay Controller (5 V)
Four isolated inputs and four relays over Ethernet, powered from USB or 5 V.
Industrial Control KiCad
The brief
Four isolated inputs, four relays and a wired Ethernet port on a board small enough to sit in a cabinet, powered from either USB or an external 5 V supply.
Two supply sources into one board is a small requirement with a real failure mode: the rails have to come up predictably whichever one is present, and neither may back-feed the other.
What we did
A compact networked controller built around the ESP32-S3-WROOM-1. It reads four isolated inputs, switches four relays and connects over Ethernet. It can be powered from either USB-C or an external 5 V supply.
- Main controller: The ESP32-S3-WROOM-1 module handles logic and connectivity, with an RGB status LED.
- Wired Ethernet: A W5500 controller with an RJ45 magjack and a 25 MHz crystal connects over SPI. Ferrite-bead filtering and decoupling on the analog supply keep the link stable.
- Isolated inputs: Four PC817 optocoupler inputs with series resistors protect the microcontroller from field wiring.
- Relay outputs: Four 5 V relays (G5Q-14) are each driven by a transistor stage with a flyback diode and indicator LED. Each relay has a screw-terminal output with COM, NO and NC contacts.
- Flexible power input: USB VBUS and an external 5 V input are combined through diodes so either source can power the board. A 3.3 V LDO supplies the logic, with a power-indicator LED.
- USB and programming: USB-C (OTG) with auto boot and reset transistors, plus manual BOOT and RESET buttons for firmware upload.
Design details
Design summary
| CAD tool | KiCad |
|---|---|
| Overview | A compact networked controller built around the ESP32-S3-WROOM-1. |
| Main controller | The ESP32-S3-WROOM-1 module handles logic and connectivity, with an RGB status LED. |
| Wired Ethernet | A W5500 controller with an RJ45 magjack and a 25 MHz crystal connects over SPI. |
| Isolated inputs | Four PC817 optocoupler inputs with series resistors protect the microcontroller from field… |
| Relay outputs | Four 5 V relays (G5Q-14) are each driven by a transistor stage with a flyback diode and… |
| Flexible power input | USB VBUS and an external 5 V input are combined through diodes so either source can power the… |
| USB and programming | USB-C (OTG) with auto boot and reset transistors, plus manual BOOT and RESET buttons for… |
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