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  • Author Author: shabaz
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E-Z USB to I2C Adapter and UART Bridge

shabaz

This E-Z USB to I2C and UART Bridge adapter is a bit of a niche project! I doubt many people may have the same precise needs as me, but I figured I’d document it, in case anyone comes across a use one day.

In brief, this project converts a Pi Pico into a USB-UART adapter, as well as a USB-I2C adapter.

This project would be useful if you wish to test an I2C peripheral, or need UART comms, or both. I used it with a device-under-test that had I2C input, and that output UART data. By using the adapter described in this blog post, I was able to wrap a complete test harness around the DUT, and run test cases from my PC.

(Note: Not relevant to this blog post, but my DUT [which I will document elsewhere] happened to be an I2C-to-UART expander – that’s a device for attaching to a microcontroller, to give it an extra UART interface via I2C, since some microcontrollers only come with one or two built-in UARTs).

If you wish to use the E-Z Adapter, the steps to build it are really simple, since it’s just an off-the-shelf Pi Pico with no additional bits. You could optionally solder I2C pull-up resistors if you don’t have that as part of the DUT.

The photo shows the E-Z adapter in use; I soldered I2C pull-up resistors on top of the Pi Pico, to pin 36 (which is a regulated 3.3V output from the Pico).

image


Here’s the connection diagram:

image

The Pi Pico can be programmed by downloading the .uf2 firmware file, and then holding down the BOOTSEL button on the Pi Pico while inserting the USB cable into the PC, and then drag-and-drop the firmware file onto the storage drive letter that appears. It will program in seconds, and start running.

In Windows Device Manager, you should see two USB Serial ports appear. One is a normal USB-UART, and the other is for the I2C adapter function.

To use the I2C adapter function, you could either type commands over a serial terminal, or you could use Python or any other programming language on the PC (very useful for creating scripts to test a DUT). The I2C adapter function is documented here (an earlier project). By the way, general-purpose input/output is also supported (so you can control relays and so on from the PC too), that's documented at the earlier project link as well. 

Thanks for reading!

 

Links

E-Z USB to I2C Adapter and UART Bridge GitHub repository

(+) USB-to-I2C with a Pi Pico: Building an Easy I2C Adapter for PC control of I2C Devices - element14 Community

  • in reply to shabaz

    Sounds a bit like the Spider Systems SpiderPort Atom terminal servers I used to use in the early 90's. They had the RS232 ports on RJ45 to save space and to be able to be patched into existing CAT3 lines.

  • in reply to shabaz

    Just remembered a bit more about that product... it had a quite neat feature, where if had a serial connection established, if you sent a "break" (easy to do, just change the baud rate on your serial terminal) it would jump to an internal menu, so you could then do neat things like switch to a different serial.

  • in reply to genebren

    Hi Gene,

    That sounds like a very useful product! I can imagine that would have been very useful especially for connecting up a load of equipment and configuring them or reading them round-robin.

    At a place I worked at, they once manufactured a device with Ethernet at one end, and then about 8 or 16 or 32 RS232 outputs at the other end (so many that there wasn't enough front panel space for DB9 connectors, so they used a high-density connector for an octopus-like cable). It was really popular for a while, since every server had a serial port on the back at the time, and no-one wanted to travel in to log on to a specific device in the event of a failure elsewhere.

  • Very cool!  I have had some projects where that feature set might have been useful.

    A bit of topic, but I have dealt with limited comm ports in several projects (specifically working with laboratory equipment, like pumps and sensors) where I needed more pumps.  At one point I developed a comm port multiplexer, where a single comm port connected to a ATmega device could drive multiple slave boards with 2 comm ports.  I built and sold several of these devices, along with a comm library to allow the slave ports to appear as actual comm port. This was more than 20 years ago.  There are far more capable devices available today.

  • Nice post.

    This device could be very useful.