Break Off a Piece of USB-C, UART, or RS232 with Anders Nielsen's Universal Serial Adapter

Fed up with closed-off-the-shelf molded serial adapters, Anders Nielsen created a versatile serial tool that can adapt to various needs. The open sourced Universal Serial Adapter supports USB-C, UART, and RS232. Nielsen invites potential collaborators to extend its functionality and, quite literally, hack the modular design.

Nielsen's Universal Serial Adapter ingeniously combines three circuits into a compact and efficient printed circuit board (PCB). A USB-C connector connects modern computers to a CH340G USB-to-Serial integrated circuit (IC). That chip provides UART-style connections to a 2.54mm header and a MaxLinear SP3243E RS-232 transceiver. The takeaway of this design is that serial hackers can use each circuit independently, adding to the tool's convenience and versatility.

The USB-C PCB provides a USB-C connector breakout when separated from the other boards. The middle circuit contains the CH340G USB-to-Serial chip, with one side going to breadboard-friendly FTDI-style headers. Technically, you can plug the entire Universal Serial Adapter in, but the third (and largest) circuit covers a lot of space if you are not using it.

A MaxLinear SP3243E IC in the third circuit makes the Universal Serial Adapter signal-compatible with vintage computers. A built-in charge pump enables the transceiver IC to handle RS-232's physical layer specifications, such as negative polarity and slew rates, while running from a single 5-volt supply. Nielsen extended the flexible chip with a lesson learned from other retro computer projects.

Interfacing with RS-232 on vintage hardware has several annoying issues. For example, you cannot directly connect two devices or Data Circuit-terminating Equipment (DCE). Instead, RS-232 requires a null modem adapter to cross several signals. Nielsen's Universal Serial Adapter eliminates the need for an additional adaptor, or dongle, to make the crossover. Nielsen learned from CommodoreZ's Cactus 6502 Toggle-Switch Homebrew Computer, who learned from TechAV a clever trick for handling RS-232 signals. A series of headers allows users to quickly reverse sets of signals by positioning pairs of jumpers in either a horizontal or vertical direction.

At the start of a video introducing the project, Nielsen discusses the origin of the word "hacker," primarily related to hardware hacking. He provides examples where "hacking" means using a hacksaw to cut or modify circuit boards. To demonstrate the Universal Serial Adapter is a hacker-friendly tool, Nielsen cuts the modules apart with a hacksaw! If you do not have a hacksaw, then a series of vias between each circuit provides a satisfying snap to break the modules apart.

Learn more about the adapter in this blog post. DIY enthusiasts can clone the KiCad Design Files and PCB gerbers from Nielsen's Universal Serial Adapter GitHub repository. Alternatively, for those who would like an assembled unit, the tool is available from Nielsen's store for €29.36 (before shipping).