What happened to cylindrical plugs?

no wonder barrel jacks were never used to transfer data…

Oh you sweet summer child. As someone who bridged the gap between analog and digital sensing systems, I assure you, they were. I think it would be hard for almost anyone who grew up/ technically developed in the all digital age to believe some of the wack-ass shit we used to do to make things work. I had a technical career in the military in the period of transition from basically hybrid analog/ digital systems, to mostly digital systems. There were PLENTY of systems that used something not any more complicated than a barrel jack for doing so. Power, communications, you name it. But these were very simple systems relative to what we do now. And the reason why matched your thinking throughout this post. They are incredibly robust, simple connectors. They can rotate without issue. They are incredibly common and can be widely versatile. They are basically bullet proof, and if need be, I could solder in a jumper or just pinch a couple wires together holding my fingers to make it work if the cable were to fail.

IIRC, and I'm long in the tooth so it might be a bit muddled, I remember it taking almost 2 days for one computer system to warm up (to quite literally warm up physically to temperature and become stable), and when we had to load the operating system, we used reel to reel digital audio tape. You quite literally had to manually move the tape back and forth to find the start byte sequence. And that system used a headphone jack to give you a digital output display (not entirely; the computer and display system for had to do the analog to digital conversion).

Round connectors were absolutely used to transfer data, for example audio and video in the form of RCA plugs and many other examples back in the day. Another example is coax cable for TV signals (both analog and digital) and also LAN.

However the lack of distinct interface channels leads to a bottleneck in bandwidth. So as the need for bandwidth increased many of those were replaced with multi pin versions. This is much harder to do with round connectors and there isn't that much benefit, so they mostly got ditched.

However round connectors still have their place, for example tiny little coax connectors found in many devices to carry signals. Wifi antennas and such are connected this way.

The 3rd gen iPod shuffles used the headphone port for USB, definitely uncommon though.

Well, those ones does it at the cost of size. In order to ensure separation they are comparatively huge.

I'm not sure how hard you're rotating a 3.5 mm cable, but yes, that sound is the sudden making and breaking of the contacts, which it's not meant to do. It will wear down the surfaces, even if the 3.5 mm tip is gold plated, since the gold is for anti-corrosion not for anti-friction.

But, the notion of cylinder housings for connectors has not died. After all, large cylinders are easy to grasp. Here is one very beefy example, often called the California Standard connector due to its use for Hollywood movie productions. This is a waterproof, twist-lock connector that also suppresses arcs if you unplug it while it's still on. It can only connect in one orientation, so you keep rotating around the center pin until it slots in. It's heavy enough to probably also double as a blackjack for self-defense lol

In not the person you replied to, and I can't speak about the engineering merits; but as a user I hate F-type connectors. They're bad enough when you have to only install them once in the lifetime of the connected device - it's the threaded screw that's the worst, I think, for which no non-technical user owns a tool beyond their fingers, from which the bevel invariably strips the flesh; although I've also bent enough of those pins trying to get something connected in an awkward place, or because I was tired, or being sloppy. It's not a connector that's convenient for amateurs, and most of its users were and are amateurs.

As a connector for multiple, frequent dis- and re-connection, it's an utter disaster. Sure, that's not what it's designed for. It was designed to be a semi-permanent extension of permanent wiring, and I'm sure it's great at that.

The context of the whole thread, though, was end-user, repeated, frequent connections for people who have to be reminded by a manual that the thing needs to be plugged in. Coax is horrible for that.

My primary complaint with the F-type connector is that it only does half the job: a proper connector should make a reliable and consistent mechanical and electrical coupling. For the latter, the F-type fails miserably, on account of having no protruding pin of its own: reusing the center conductor as a "pin" is at best slapdash, and at worst fails to account for inconsistent conductor cross-sections.

When affixing an F-type connector onto a new segment of coax, unless great care has been taken to slice the cable cleanly, the center conductor often ends up with a arrow-shaped tip which also flattens the round cross-section into an oval. This tip is now a minor danger to people, in addition to no longer being assumed as round. This certainly doesn't help with reliable mating later.

Furthermore, a solid copper tip is not ideal for a connector, unless the opposite coupler that grasps the tip is made of copper as well. But copper can't be used to make springy receivers, so inevitably another metal must be used. But the prevailing composition of contacts for connectors are either solid brass or are plated (eg gold). But a sharp copper tip will end up scratching the mating surfaces over time.

And this is just the start of the F-type's follies. The user experience of turning a 7/16" fine thread in narrow spaces is exhausting. With no consistent specs for the F-type, some cheaper connectors have the thinnest possible hex head to fit a wrench on. Compression F-type is better, but then we have to compare to other connectors.

In the broadcast and laboratory spaces, BNC is the go-to connector, with easy mating and quarter-turn engagement. It also comes in 50 and 75 Ohm variants (albeit confusingly). In telecoms, the SMA connector is used for its small size, and larger coax might use the beefy N connector. Some of these variants are even waterproof. Solderless is an option. All these connectors are rated by their manufacturers for a minimum number of mating events.

In all circumstances, according to this chart, the RF performance of BNC, SMA, and N are superior to F-type, which has only ever been used for TV, CCTV, and certain low-frequency clocking systems. I'm not sure what you mean by "rated to absurd frequencies", but surely SMA's (up to) 25 GHz rating would be tremendously and wildly insane in comparison to 1-2 GHz for F-type.

So that's my beef. It's just a bad connector, used only because it's cheap.

i keep hearing that F stands for Flimsy. no idea where that came from, unless something is seriously wrong with crimping technique. i guess there's a tradeoff between CCS or copper cable with durability of pin/center conductor vs bending radius, and some people don't like how it turns out, while ignoring that it's cheap and not really designed for multiple disconnections

but yeah, as long as everything is matched good-enough then it's a cheap way to connect low loss, cheap cable (75 ohm only. otherwise i'm in the N/SMA/BNC camp, UHF connectors are unreasonably obsolete)

i don't think you're supposed to hotplug soldering iron tip. besides it's a simple thing, isn't that just two resistors - one for heating element and another for measuring temperature? hard to break that. not sure about how ipod shuffle worked or what precautions were needed. also today USB can deliver power at higher voltages than it used to

Could they even be hot swapped? I don't remember trying. I remember my dad getting a CD-RW drive with a USB-A connector, I had to reboot to get the computer to recognize it, but that was Windows 95 or 98.

In a sense, we already have one. And it's used on the vast, vast majority of desktop computers, it's the standard for removable cords on electric kettles around the world, and it shows up in all data centers. I'm talking about IEC 60320, sometimes just called the "IEC connectors" or for one very specific connector, the "PC plug".

For the task of attaching AC power to an appliance, this is probably the one with the greatest adoption worldwide. And there absolutely could be a wall-mounted version of these, the same way that datacenters essentially have power strips -- ok, they're RPCs lol -- with these connectors.

Their only noticeable drawback is that the voltage can be anything up to 250v. So plugging 120v appliances into an Italian 230v outlet would be bad. But this family of connectors -- formally called "couplers" -- was meant to match current-capacity, where a mismatch would cause a fire due to overload. It's still the user's responsibility to check the voltage, in the same way that buyers have to check the type of battery they need for a remote control (eg AA vs AAA).