Alan's Tiny WIZnet W55RP20 Board Hides a Secret Ethernet Connection in Its USB Type-C Connector

Mononymous maker "Alan" has designed what he proclaims as "the smallest Ethernet module in the world," making use of a USB Type-C connector's extra capabilities — and powered by the WIZnet ioNIC W55RP20, which combines the company's W5500 Ethernet controller with a Raspberry Pi RP2040 microcontroller in a single surface-mount package.

"The main chip of this module is WIZnet's new chip, the W55RP20," Alan explains. "This chip combines Raspberry Pi's RP2040 and WIZnet's W5500. Think of it as adding Ethernet functionality to the RP2040. This makes it perfect for small projects requiring Ethernet connectivity. The design was carried out to create a small microcontroller, similar to Pimoroni's Tiny 2040 or Seeed Studio's XIAO RP2040. It's a similarly sized board, but with Ethernet capability."

At first glance, Alan's board design seems to lack Ethernet connectivity — despite the use of the WIZnet's W55RP20 chip. Like the boards from which Alan drew inspiration, there's only a single USB Type-C connector for data and power plus 0.1" general-purpose input/output (GPIO) pin headers at either side. The secret: the USB Type-C connector is pulling double-duty as an Ethernet port.

"Even with this groundbreaking design, there is a problem," Alan admits. "While this module is designed to enable Ethernet through a USB Type-C connection, the other modules it communicates with are not. All Ethernet modules equipped with RJ45 that we use operate based on their specific pinout. Therefore, the pinout of this module must be aligned with other Ethernet equipment. For now, this requires using a jig."

The jig in question is a breakout board that connects to Alan's microcontroller board over a USB 3.0 Type-A to Type-C cable, then provides USB 2.0 and Ethernet RJ45 connectivity at the other end. As a result, Alan's claim to have made "the smallest Ethernet module in the world" could be called into question through the need to add the footprint of both boards together — but, in Alan's defense, the breakout board could be replaced with a custom-made Y-splitter cable to bring the size back down again.

The project is documented on the WIZnet Makers site, split into part one and part two.