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Developer Francis Stokes found himself in need of a USB-UART adapter, and rather than wait for delivery opted to put one together — using components lying around the home lab to create a "jank UART to USB cable."

"My home 'lab' is, unfortunately, a manifestation of the unwinnable, uphill battle against entropy. The latest victim to the sprawl of boards, prototypes, and other miscellanea was my little Adafruit CP2104 USB to serial converter," Stokes explains. "As far as I can tell, it has literally dropped off the face of the Earth.

"Of course, the first thing I did was hop online to order a new converter. Shortly thereafter, however, I came to the sudden realisation that this is something I should be able to make myself. I mean, what's the point in having a lab in the first place if you're not going to use it for this kind of thing! This is a yak that simply needs to be shaved."

Usually of use in communicating with devices which lack their own USB serial capabilities, USB-UART bridges provide a TTL serial port when connected to a machine's USB port. Hook the other end to a device with its own TTL serial port, and you're ready to talk UART — either for debugging or for reprogramming. If your desk actively eats your USB-UART adapter, though, things become more challenging — which is where Stokes' creation comes in.

"I happened to have this old Arduino Duemilanove board just laying around, gathering dust, which has an FT232RL chip from FTDI to convert serial UART to USB," Stokes explains of the primary source of scavenged parts for his homebrew UART adapter. "The first thing I did was fire up the hot-air rework station in order to de-solder the chip, along with the two capacitors just above it."

With the surface-mount chip in-hand, Stokes used an unpopulated SSOP4 breakout board — carefully re-soldering the component using a fine-tipped soldering iron — to provide a basis for the adapter. A knife and a sacrificial USB cable provided the USB end of the equation, and a careful look at FTDI's data sheet for the part revealed exactly what needed to be soldered where.

"Notice the Kapton tape and hot glue mess," Stokes says of the finished adapter. "That's really there to re-enforce the flimsy solder connections, and to stop anything from shorting later on, but it definitely helps with the scavenged look. So the jank cable was a success! I'm still happy that a professionally made adapter is coming in the next few days, but damn if it doesn't feel cool to know that I can whip up my own tools in a pinch."

Stokes' full write-up is available on GitHub.

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