UsbGpib: an open USB to GPIB adapter you can build yourself

The reason the project exists is the price of commercial adapters

UsbGpib is a versatile, cheap and portable USB to GPIB converter based on the USBTMC class, and the origin story in the readme is unusually direct.

The author started it about seven years ago as a weekend project: an open, MIT licensed way to talk to GPIB instruments without paying for a commercial adapter costing 800 dollars or more. GPIB is the older parallel bus used by laboratory instruments from oscilloscopes and bench multimeters to power supplies and spectrum analysers, and it predates USB by decades, so instruments that have it usually have nothing else.

That price figure is the whole motivation. A 300 to 400 dollar adapter to talk to a 3000 dollar instrument that already has a GPIB port is a strange ratio, and the response was to publish the design.

The repository layout matches that intent. There is an HW directory for hardware, SW for software, Housing for enclosures, Tutorials with its own readme, Updates.md for the running log, and a pictures directory. The primary language is C, which is what you would expect for the firmware side, and the licence is MIT.

The readme also links a separate project as an example of what can be built on top: a Python GUI by a third party for controlling the Tektronix DMM 4050 six and a half digit precision multimeter over UsbGpib, with measurement logging to CSV. That example is the clearest statement of the adapter's purpose, since it is a full instrument front end built on someone else's USB to GPIB bridge.

V3 became a product, and V1 and V2 stayed open

The most important thing in this repository is a decision the author made after seven years, and it is set out at length in the readme.

Version 3 of the hardware is called GPIBee, and it is now available as a commercial product with USB-C and Ethernet with power over Ethernet, VXI-11 with multiple simultaneous sessions, and claimed throughput of 3.5 to 5 times the speed of V2, in a proper enclosure with support behind it. The stated reason for going commercial is straightforward: it provides a sustainable way to keep the work going rather than depending on spare evenings, and it funds the things a hobby project cannot, namely CNC machined and EMI shielded enclosures, firmware QA and proper support. The author also frames it as a legitimate path forward that undercutting clones cannot quietly erase.

What matters for anyone reading this repository is what has not changed. The author is explicit that V1 and V2 stay exactly as they are, MIT licensed, fully open, with schematics and firmware included, free to build and modify. And the maintainer states that UsbGpib will keep being maintained, answering issues and keeping it working, alongside GPIBee rather than instead of it.

So the licence boundary sits at a version number, not at a repository. If you are building V2 hardware, everything you need is here under MIT. If you want the faster V3 with the enclosure and the support, you are buying a product.

The readme is also direct about the origin of the decision. The author is comfortable with people and companies building their own UsbGpib, and works with official partners including Elecrow and Binho, but says that unrelated manufacturers turning V2 into a business at scale with no attribution back to the project sat badly, and that this was the deciding factor in what V3 should be.

Prebuilt adapters exist, but the design files stay in the repository

There is a second form of commercial arrangement inside the same project, and it is a lighter one than GPIBee.

The readme offers two routes for people who would rather not solder. In the United States the UsbGpibV2 can be ordered from several sources, including the distribution partner Binho LLC, and the readme points at Binho and DigiKey for that, noting that Amazon US has a listing with no stock at the moment but is worth checking. Worldwide, the author has teamed up with Elecrow to bring ready to roll GPIB to USB converters, which the readme says come fully assembled, programmed, housed and tested, and that they match the V2 version described in the repository one hundred percent.

The framing of this part is careful, and the wording matters. Offering pre-built adapters is described as a convenience for people who would rather skip the build, not as going fully commercial, and the readme says all sharing, support and collaboration will remain fully open. Offering the same hardware in two forms is a reasonable arrangement for a design that people are already building by hand.

The important sentence for anyone deciding is that the full design files are located in the repository in case you want to build the devices yourself. Whatever you buy, you can build.

There is also a FUNDING.yml file at the repository root, which is the mechanism GitHub uses for sponsorship, and a Tutorials directory that the readme flags as new, plus an Updates.md that the table of contents describes as the detailed visibility into changes.

What the hardware and software directories actually contain

The readme introduces the project as a versatile, cheap, portable and robust USB to GPIB converter based on the USBTMC class, and the directory structure shows what that means in practice.

The USBTMC class detail is the part that determines compatibility. Because the converter presents itself as a USBTMC device rather than as a vendor specific device, the host operating system sees a standard test and measurement class instrument, and instrument control software that speaks that class can drive it without a vendor driver. That is what makes the adapter usable with existing tooling rather than only with software written for it.

The HW directory holds the hardware design, and the Housing directory holds the enclosure. Both being in the repository is the part that distinguishes this from a firmware-only project: the enclosure files are what let the design be reproduced rather than approximated, and the author points at CNC machined and EMI shielded enclosures as one of the things the commercial version funds. Housing a USB to GPIB converter is not trivial, since a GPIB connector is heavy and the cable has to be supported mechanically.

The SW directory holds the firmware, and the primary language of the repository being C says what you would expect for code that runs on the adapter itself. The scope of that firmware is bounded by the USBTMC class, so it implements the standard message handling rather than a proprietary protocol.

The readme also has sections for using the device, for setting and getting parameters, and a testing status section. The parameter section is the part that tells you about control: instrument parameters are read and written through the same bridge, which is how the third party multimeter GUI can both command an instrument and log what it reads.

What to check before you build one

A few practical checks are worth making before committing to a build.

First, confirm the instruments speak GPIB and that you need a computer side adapter rather than a modern interface. The project is about bridging an older parallel bus, so an instrument that already has USB or LAN changes the calculation entirely.

Second, decide between the two hardware versions on practical grounds rather than on the announcement. V2 is fully open with everything needed to build it in this repository. V3 is faster, adds Ethernet with power over Ethernet and VXI-11 with multiple simultaneous sessions, and is a commercial product with an enclosure and support behind it. The readme gives the speed claim as 3.5 to 5 times V2, which is the main technical difference to weigh.

Third, read the testing status section and the tutorials before you order parts. The readme flags the tutorials directory as new, and the testing status section is the honest place to learn how much of the design has been validated. Seven years of user reports exist, and the readme mentions them directly, describing people who soldered it into home labs, universities and repair benches, and it names the kind of feedback that comes with that, from bug reports and emails to late night calls from people debugging their own build.

Finally, plan for the fact that you own the thing. There is no vendor to call, and the maintainer says plainly that ongoing support for the open versions continues alongside the commercial one rather than being replaced by it, but the realistic reading of a single maintainer with day job commitments is that the community forum and the issue tracker are where a hardware question gets answered. That is a normal arrangement for open hardware, and it is also the reason the third party front ends matter, since a working example is often faster than a support thread.

Editorial conclusion

Adopt UsbGpib if you own GPIB instruments and want a cheap, portable USB adapter that you can repair, modify or build yourself rather than buy a commercial unit, and you are comfortable with hardware and firmware work. Do not adopt it expecting a supported commercial product, because the third version became a commercial product called GPIBee rather than an open one, while V1 and V2 stayed open. Before you commit, read the hardware and software directories in the repository, confirm your instruments speak USBTMC, and check the testing status and tutorial pages so you know which part of the design is documented to what degree.

Frequently asked questions

Official sources

1. Issues
2. License: MIT
3. README
4. xyphro/UsbGpib on GitHub