G2U

G2U

Andrew Martin, acramonics, 2026

G2U is a PCB for a GPIB to USB adapter using an Arduino Nano 3.

GPIB is a vendor-neutral interface for controlling equipment and logging data. While rather outdated, and largely replaced by USB and Ethernet, some equipment still uses it and there are many second hand devices (such as multimeters) that use it including the well-regarded Solartron 7150+.

A video on GPIB (also known as IEEE-488) is on YouTube and details are on Wikipedia.

Hardware

The original circuit and software was by Rudolf Reuter and modified by @TheHWCave. Rudolf's blog, where this was described, doesn't seem to be available any more (as of March 2026), but @TheHWCave provides a detailed description of the circuit on YouTube (see the screenshots in the SourceImages directory). He builds it on stripboard and uses an Arduino breakout board, so I decided to create a PCB instead. He was unable to obtain a PCB-mounted Centronics-style (Series 57) 24-pin connector. These are now easily available from AliExpress (at about £2.50 with free postage if you spend more than £8.00), and I have used a PCB-mounted male connector that can plug straight into the back of the hardware, so you don't need to worry about cables.

There is another page with a discussion of creating a GPIB/USB interface, but note that this uses different pin assignments and different software.

Software

@TheHWCave provides the code for the Arduino Nano 3 and a logger script on GitHub.

He provides an update video which explains how to address a problem with the Arduino losing its software when the USB us disconnected, but the GPIB connection is still present. The GPIB seems to provide some partial power to the Arduino and he provides instructions on setting a brown-out fuse in software.

I provide a summary of all the necessary information on this page.

The PCB

As is often the case with my PCBs, you will require my ACRM_KiCad_Libs to provide the footprint for the 24-pin male Centronics-style connector. You will need a version from March 2026 or later.

Bill of Materials

• Arduino ATmega Nano 3.x with USB (ideally USB-C) [1 off]
• 6K2 0.25W resistors (R1-R16) [16 off]
• 120R 0.25W resistors (R17-R32) [16 off]
• Centronics-style 24P 'Series 57' male connector [1 off]

The PCB is 78.05mm x 71.40mm so you will need a plastic case to accomodate this. The Centronics-style connector projects from the board so will need a suitable cutout. The USB connector is set back on the board, so it's not easy to plug a cable in and out once the board is in the case, but, since the GPIB sockets are usually at the back of equipment, the expectation is that the board and the cable will be left plugged in.

Ardunio to GPIB connections

This table is expanded from a table shown in @TheHWCave's video (see the screenshot in the SourceImages directory) and shows which connections from the Arduino go to which pins on the GPIB. The Arduino pins are shown with the pin number (from 1-30) and the position on the left (L) or right (R) column of pins - both counting from the top.

Note that each GND pin in the GPIB connector is paired with one of the data lines in a twisted pair. Pin 12 is connected to the cable shield. See GPIB on WikiPedia. In this application, this is rather irrelevant as everything is connected to a common ground.

The Brown-Out Fuse

As described above, @TheHWCave provides an update video which explains how to set the 'brown-out fuse' on the Arduino to prevent it losing its software.

The 'extended fuse byte' has three bits that set the Brown-Out Detector voltage level ('BODLEVEL'). When the voltage falls below this, the chip is disabled.

The values for the BODLEVEL bits are as follows:

(*) Since bits 3 to 7 are not used, these can all be set to zero and the Hex values reflect that.

By default the fuse is set to #FF, the BODLEVEL bits are therefore set to binary 111 which means the brown-out fuse is switched off.

@TheHWCave selects a BODLEVEL of 4.1V (minimal) so sets the fuse to binary 100 (#04) for 4.1V cutoff.

Instructions on how to do this are provided below.

Software Installation

You will need:

• A USB cable to connect your computer to your Arduino Nano
• An ICSP programmer with a 6-pin header adapter to connect to the Nano. There are instructions online to use another Arduino for this purpose or you can buy a standalone programmer such as the USBASP programmers available from Amazon (amongst other places).

You will need the software available from https://github.com/TheHWcave/GPIB-to-USB

Using this is explained in the video at https://www.youtube.com/watch?v=RaLirRvSngk

Step 1: The Arduino IDE

Install the Arduino IDE as described on the Arduino Web Site

Step 2: Configure the IDE for the Arduino Nano ATmega chip you are using [OPTIONAL]

Different Arduinos use different chips which have different signature bytes and this needs to match the programmer:

If the configuration doesn't match your chip then, for example, the Arduino IDE may call AVRDude (used to set the fuse) expecting to find an ATmega328P, but AVRDude finds an ATmega328PB and stops.

The configuration can be set in a configuration file or by manually re-running the failed command, but correcting for the appropriate chip. (See instructions below.)

If using Linux, the easest thing to do is create configuration file: ~/.avrduderc containing:

part parent "m328"
    id                  = "m328p";
    desc                = "ATmega328P";
    signature           = 0x1e 0x95 0x14;
    ocdrev              = 1;
;

setting the id, desc and signature as required depending on what ATmega chip you have with signature bytes set as per the table above.

Alternatively you can allow AVRDude from the IDE to fail and then run the fixed command manually as described below.

Step 3: Setting the Brown-Out Fuse

I will write a more detailed version when I have verified this on a couple of Arduino Nano boards. This is largely in note form!

As described above, you will need a second Arduino, or an ICSP programmer spported by the Arduino IDE, to set the fuse. The IDE runs the AVRDude software to perform the programming of the Brown-Out Fuse.

To set the fuse from the Arduino IDE, proceed as follows --- to be written

See:

• https://forum.arduino.cc/t/is-there-brown-out-detection-for-arduino-uno/124777/18
• https://electronics.stackexchange.com/questions/229189/atmega328p-how-is-brown-out-detection-supposed-to-work
• https://forum.arduino.cc/t/unable-to-set-fuses-on-atmega328p-using-avrdude-in-command-prompt-windows/1067499/5

Set the IDE to run in verbose mode so you can see what it is doing as described here

If you have configured the IDE properly, then it should work with no errors. If you haven't then the AVRDude software will fail since the chip's signature doesn't match what the software expected. The workaround for this is described in @TheHWCave's video at https://www.youtube.com/watch?v=DAS1KVU_FaA and summarized below.

If AVRDude fails, simply copy the failed command from the upload window and run it from the command line instead, correcting the errornous chip type. For example, assuming the Arduino IDE is configured for an ATmega328P and your Nano has an ATmega328PM and assuming that the IDE is installed in a directory pointed to by the environment variable $ARDUINO (e.g. $HOME/arduino-1.8.9), you might see the failed command to be:

$ARDUINO/hardware/tools/avr/bin/avrdude \
   -C$ARDUINO/hardware/tools/avr/etc/avrdude.conf \
   -v -patmega328p \
   -cusbasp -Pusb -e -Ulock:w:0x3F:m -Uefuse:w:0xF4:m \
   -Uhfuse:w:0xDA:m -Ulfuse:w:0xFF:m

and you would modify this to

$ARDUINO/hardware/tools/avr/bin/avrdude \
   -C$ARDUINO/hardware/tools/avr/etc/avrdude.conf \
   -v -patmega328pb \
   -cusbasp -Pusb -e -Ulock:w:0x3F:m -Uefuse:w:0xF4:m \
   -Uhfuse:w:0xDA:m -Ulfuse:w:0xFF:m

(note the change in the 3rd line) and run it from the command line

Step 4: Restoring the bootloader

Setting the fuse erases the memory, so you then need to restore the bootloader.

Instructions on doing this from the IDE are described here

Alternatively, you can do it from the command line using AVRDude:

~/arduino-1.8.9/hardware/tools/avr/bin/avrdude \
   -C~/arduino-1.8.9/hardware/tools/avr/etc/avrdude.conf \
   -v -patmega328pb \
   -cusbasp -Pusb -Uflash:w:./optiboot_atmega328.hex

This also allows the latest bootloader to be downloaded and installed. See

• https://forum.arduino.cc/t/how-do-i-install-optiboot-on-the-newest-arduino-ide/345443
• https://github.com/Optiboot/optiboot

(The latest, as of March 2026, is https://github.com/Optiboot/optiboot/releases/download/v8.0/package_optiboot_optiboot-additional_index.json)

Step 5: Installing the Arduino software

You can then remove the in-circuit programmer and upload the GPIB-to-USB software sketch in the normal way from the Arduino IDE through the USB cable and with the newly installed boot loader.

To be written.

Future plans

In future, I may do an SMD version to minimize the size and weight!