GoKawiilIf you experimented with embedded devices like a Raspberry Pi or had a failed OpenWrt router firmware update, you know the drill: connect a USB-Serial TTL adapter to the three magic pins on the motherboard, labeled RX, TX and GND.
This opens up the gates to a new, otherwise undiscovered universe — the world of early stage bootloaders, built-in diagnostics, low-level recovery, etc. There is a good reason this is not exposed to the average customer: this domain is not for them. It’s a dangerous place, one can do serious damage when let loose.
Gordian knot, 21st century edition, and some USB to TTL adapters
But we’re no average customers, are we? No, we unceremoniously keep a strand of unprotected Dupont-style breadboard jumper cables connected to these three UART TTL pins, dangling out through a little hole we drilled in the device enclosure. Because — duh — you never know when you’re going to need to connect to them again, right?
This is not only unseemly, it is also neither reliable nor safe. These wires are not meant to be bent often, which I learned the hard way in the case of my trusty NanoPi R4S, which would no longer accept inputs.
Also what do you connect the jumper cable to? Normally a USB-TTL adapter, which either comes in the cheap short and PCB-only shape or in the “keep me directly connected even if you stumble over my long cable” variant, and either way, you keep them connected because — duh — you don’t want to unnecessarily strain the Dupont wires…
Neither solution is appealing: you shouldn’t keep something permanently connected unless necessary (from my own experience, the USB adapters get back-fed some current from the RX/GND pins even when not connected on the USB end), and you shouldn’t keep a rather unprotected PCB hanging from three tiny wires. We can do better than that!
Before: TTL wires and USB serial adapter dangling out of an OpenWRT router — After: a clean, beautiful Juliet connector
I have now found my favorite solution to the problem, and I’m therefore proposing a new standard (obligatory xkcd 927 reference), which hopefully catches on: Julet connectors.
Variety of Julet connectors (source: AliExpress)
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