Olimex UEXT-CH390 Adds Wired Ethernet to Pico and ESP32
The Olimex UEXT-CH390 is a €4.95 open-source module adding 10/100 Ethernet to Raspberry Pi Pico and ESP32 boards, with ESPHome and Home Assistant support.
Wi-Fi is the default for most maker sensors, but it is not always the best choice. Thick walls, crowded 2.4GHz bands and battery-hungry radios all push some projects back toward a cable. Olimex has a cheap answer for that: the UEXT-CH390, a small open-source hardware module that gives microcontroller boards a wired Ethernet port.
- The UEXT-CH390 adds 10/100 Mbps Ethernet over SPI using the WCH CH390 controller
- It targets Raspberry Pi Pico, Pico 2 and ESP32-S3, C3, C5 and C6 boards without built-in Ethernet
- The module measures 50 x 21mm and runs from 3.3V via the UEXT or pUEXT connector
- Olimex lists it at €4.95, with pre-order availability expected on November 9, 2026
How Does the UEXT-CH390 Work?
The WCH CH390 chip combines the Ethernet MAC and PHY, so the host microcontroller does not need its own Ethernet MAC. It connects over SPI, and the controller itself supports clocks up to 72 MHz. It also has a 16KB packet buffer, auto-MDIX, IPv4 and IPv6 checksum offload and a factory-programmed MAC address, so no extra EEPROM is needed.
One thing to know before you buy: the CH390 does not have a hardware TCP/IP stack. The host MCU runs the network protocols. On an RP2040 or ESP32 that is a fair trade for the price, but it does use some CPU time and memory.
The board carries an RJ45 jack, a standard 10-pin UEXT connector and a smaller 1.0mm-pitch pUEXT connector. Those connectors are Olimex's own expansion standard, which keeps cabling simple on its boards.
Does the UEXT-CH390 Work With ESPHome and Home Assistant?
Yes. ESPHome already supports the CH390 on ESP32 devices, and Olimex wrote a driver to bring the same support to RP2040 boards. The company tested it on its RP2040-PICO30U-16 board running ESPHome 2026.9.0, connected through a 100mm pUEXT cable.
With that firmware the board picks up an address over DHCP and appears automatically in Home Assistant. It takes over-the-air updates through Ethernet after the first USB flash, and serves a local web page that works with no internet connection at all. Olimex publishes a ready-to-flash UF2 file plus the source code and config files. For a deeper ESPHome setup, our look at the Apollo ESP32-C6 ESPHome starter kit covers the software side.
There is also a Raspberry Pi Pico SDK example that uses the lwIP stack and a simple web server, so you are not locked into ESPHome. Arduino IDE support is listed too.
Who Should Use a Wired Ethernet Module?
Wired networking makes the most sense for sensors in garages, basements and outbuildings, for power-over-cable style installs and for anything that must stay reachable. At under €5, it is easy to add to a build. Olimex fans may also remember the Neo6502kbd retro keyboard computer, another of its open hardware designs. Find more boards and add-ons in our mini computer section.
Sources: Olimex product page — accessed November 6, 2026; CNX Software — November 6, 2026.
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