this post was submitted on 01 Mar 2025

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What happened to cylindrical plugs? (lemmy.world)

submitted 2 days ago by [email protected] to c/[email protected]

63 comments fedilink hide all child comments

Barrel jacks were awesome, they could go in any orientation. The only downside was the many different forms of barrel jack and lack of a standard. My question is: why isn't there a cylindrical USB port? You would be able to rotate it any way you want within 360 degrees!

As a matter of fact, why isn't there a cylindrical power plug? You'd get the benefits of a recessed plug like Type-C (EU) and Type-F (Schuko), you'd get the benefits of reversible plugs like Type-A (North American) and more so as you get 360-degree rotation, and it would be MUCH harder to break/bend compared to two flimsy pins (the UK plug has three thicker pins, but a chunky cylinder would be much more difficult to bend than the pins)

If it was a hollow cylinder (a bit like a vacuum-insulated water bottle), you could feasibly fit some small electronics in it, so things like flush low-power USB chargers and smart home sensors could be made.

The contacts would likely need to be outside the cylinder, similar to the "neutral" pins on Schuko plugs. There would likely need to be some plastic tabs to keep the power bits from touching the non-power bits, and then the socket itself would be able to freely rotate.

Actually, why don't regular sockets freely rotate? Then it would solve all the issues of non-reversible plugs not able to go upside down and reversible plugs not able to go sideways.

Speaking of cylindrical objects, what happened to camcorders? They sound like the most comfortable and easiest way to record videos, with straps and everything. They were compact, portable, and wasn't heavy as all heck.

this is my rant about cylinders, thank you for your time.

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[–] Shadow 68 points 2 days ago* (last edited 2 days ago) (4 children)

Usb c has 24 pins. A typical barrel / stereo style jack has 2 - 4. The connector would have to be absolutely huge to carry the number of wires.

Power plugs are similar problems. You need 3 wires and you can't risk the pins crossing over each other and shorting out. You don't care about that on your headphones due to the low voltages. Wall plugs need to be fully isolated and safe.

[–] [email protected] 16 points 2 days ago (3 children)

oh yeah usb has loads of pins for data. no wonder barrel jacks were never used to transfer data…

oh yeah designing an idiot-proof power plug that can be rotated 360 degrees would be challenging ad well

[–] [email protected] 9 points 1 day ago (1 children)

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).

[–] [email protected] 1 points 1 day ago

oh interesting

[–] [email protected] 16 points 2 days ago (2 children)

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.

[–] [email protected] 1 points 1 day ago

oh cool

[–] [email protected] 4 points 1 day ago

Coax has only 2 conductors and it keeps impedance constant, unlike audio jack

[–] [email protected] 2 points 1 day ago

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

[–] [email protected] 11 points 2 days ago

to add to this answer, those 24 pins would have to be aligned correctly.

so, you'd have this problem, but worse because because it's round and not basically flat:

[–] [email protected] 3 points 2 days ago (1 children)

Cordless kettles manage to connect mains power with a round, freely turning connector, so it can be done safely

[–] [email protected] 11 points 2 days ago

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

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[–] [email protected] 34 points 2 days ago (2 children)

A cylindrical connector would be fine for connecting one or two conductors. But more than that and it starts to become a nightmare to design, and even worse to build and use reliably. Classic examples include the venerable RCA connector, the BNC connector for radio signals, and IMO the worst connector to ever exist, the F-type connector used for TV coaxial cable.

With just two conductors, a cylinder can have have a concentric shape, where the inside is a pin and the outside is a shell. But you'll notice that although all these connectors are circular, they're hardly designed to rotate while attached. You generally have to remove or at least loosen them before trying to turn them. Or you still try it and the TV picture might flicker a bit. The problem is one of electrical contact.

The engineers that make connectors go through painstaking efforts to get the conductive surfaces to align -- or "mate" as they say -- because if they don't, the signal quality drops like a rock. It's already hard enough to get cheap connectors to reliably align, but now you want them to move relative to each other? That's tough to build, and moving surfaces will eventually wear down.

Even worse is that circular shapes tend to have poorer mating, because manufacturing tolerances for curves is wider than tolerances for flat surfaces. We actually don't want to make round contacts, if a rectangular shape would suffice. Flat contacts are simpler to produce and generally more reliable [citation needed].

But even more intractable is the matter of matching the pinouts. Here is the pinout when looking at the connector of a USB C cord:

Even without understanding what each pin does, it's noticeable that certain pins are the same whether you flip the connector over. In fact, they even label them that way: pin A12 on the top-right is also B12 on the bottom-left. The most damaging scenario is if USB 5v power was sent down the wrong pin, but it's very clear that the VBUS pins -- which are the 5v power -- will always be in the same place no matter the cord orientation.

The only pins which are different upon inversion are the data lines -- anything with a + or - in the name -- or certain control signals which are intentionally paired with their opposite signal (eg CC1 and CC2). The USB C designers could have packed way more data pins if they didn't have to duplicate half the pins to allow flipping the connector over. But that design choice has made USB C easier to use. A fair tradeoff.

And that's the crux of it: in engineering, we are always dealing with tradeoffs, either for performance, cost to produce, ease of use, future compatibility, and a host of other concerns. Wanting a cylindrical connector could certainly be a design goal. But once it starts causing problems with alignment or manufacturing, there will inevitably be pushback. And it's clear that of all the popular connectors used today, few are cylindrical.

Heck, even for DC power, the barrel connector has given way to more popular designs, like the Anderson PowerPole or the XT family of connectors, because the market needed high-current connectors for drones and Li-po batteries. Granted, the XT connectors are basically two cylindrical connectors side-by-side haha.

[–] [email protected] 7 points 2 days ago (1 children)

woah that’s a very in-depth answer. yeah makes sense that cylindrical connectors aren’t actually designed to rotate a bunch. I assume it would be something similar to weird crackling sound when you turn an 3.5mm jack cable too hard?

[–] [email protected] 7 points 2 days ago* (last edited 2 days ago)

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

Hubbel California standard connectors CS6365 and CS6364

[–] [email protected] 3 points 2 days ago (3 children)

What's your beef with the F-type connector? The centre pin is the coax core, compression tool to terminate the coax, solid connection, rated to some absurd frequencies, all round easy connector, no soldering or extra pin required.

Source: I installed two-way satellite dishes for a time and still use those connectors on my HF antennas as a radio amateur - yes, I know, 75 Ohm - can't say it's ever stopped my 10 mW beacon from being heard 13,945 km away.

[–] [email protected] 4 points 1 day ago (1 children)

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.

[–] [email protected] 2 points 1 day ago (1 children)

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.

so you want BNC

[–] [email protected] 4 points 1 day ago (2 children)

BNC is better, but I've only encountered it, like, twice.

Honestly, I've never been happier since USB-C took over. I compare today to the early 90s and having 8-12 different connectors - two of which looked identical but were incompatible - to hook up a single Sun workstation. I clearly remember dreaming of a day when there would be a single connector for everything, and we're really close. Higher wattage demands and video connectors (HDMI, DP, DVI) are the only hold-outs - and I'm not sure why USB-C hasn't conquered video yet, unless it's a cost thing, because it's certainly capable.

[–] [email protected] 3 points 1 day ago* (last edited 1 day ago)

you don't see BNC as often because it's more expensive, bulkier, requires different crimping tool and has a separate soldered pin. but if you need to connect and disconnect things often and quickly, then it's a good connector. i bet you've seen (RP-)SMA a lot instead, but this one is also more expensive than F, has separate pin and is too small to easily make a connector for common 75 ohm cables. reducing diameter would mean higher loss

[–] [email protected] 2 points 1 day ago (1 children)

USB-C likely will take over video eventually. I use it for video on two out of three of my monitors and the Nintendo switch can be used that way.

[–] [email protected] 3 points 1 day ago (1 children)

I've been half-assed monitor shopping, and the USB-C capable ones are still far more expensive; they exist, they're just pricey. I'll consider USB-C to have "won" when the price difference is negligible.

[–] [email protected] 2 points 1 day ago

I agree, but somehow the low end portable monitors seem to already have USB-C support. I bought a monitor for like $60 and it had USB-C.

I'm not quite sure why regular size monitors are lacking the support.

[–] [email protected] 2 points 1 day ago* (last edited 1 day ago) (1 children)

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.

[–] [email protected] 2 points 1 day ago

I saw that chart too. When you click on the F-type link you learn it's rated up to 4 GHz. The summary table is off for several connectors.

You cannot argue that the mating is poor if it's rated to 4 GHz.

There is nothing wrong with using the centre pin of the coax, it's one less join in the chain and it's rated at over 500 matings. It's not for lab equipment, but if you want to connect something and leave it there for the next decade, there's nothing better.

[–] [email protected] 2 points 1 day ago* (last edited 1 day ago) (1 children)

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)

[–] [email protected] 3 points 1 day ago

For my shack where I move stuff around, testing gear, radios, switches, etc. I've standardized on SMA, on my feed line which hasn't changed or been disconnected for a decade, F-type.

[–] [email protected] 16 points 1 day ago* (last edited 1 day ago) (2 children)

There are two immediate problems with round USB. First one is that audio jack carries no power and it's generally rather harmless for finals or microphone to have some contacts shorted or crossed for time when plug is inserted. USB, let's even day just 4-pin, carries power and i'm not sure how well would either of devices react to having data bus connected to +5

The other problem is that USB is proper radiofrequency connector, unlike audio jack where anything goes. This means it has to be shielded and impedance has to be some specified value, which in practical terms means that there's some specific ratio of metal to plastic and shape of conductors that has to be used. Barrel plugs would have way too low impedance and already bulky connector needs extra shielding which makes it even bigger

[–] [email protected] 1 points 1 day ago

that makes sense. those connectors would have to be pretty huge

[–] [email protected] 2 points 1 day ago (1 children)

Ipod Shuffle and the TS80P soldering iron both use TRS for power transfer.

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[–] [email protected] 4 points 1 day ago

I'm no expert, but I'll give you my two cents. I play bass guitar and there are two types of connectors between amplifier and speaker cabinet. First one is plain barrel jack, second one is Neutrik. I've been talking with local amp maker and he said something like this: "jack is fine with low wattage, but with more power you'd do better with neutrik - it has much larger contact area " So I believe this is similar problem. We were speaking like 400-600W of power where jack starts to be worse. How about vacuum cleaner or kettle? Or similar appliance that can do 2kW... Small contact and higher drain means more heat generated in that spot.

[–] [email protected] 8 points 1 day ago (1 children)

Speaking of cylindrical objects, what happened to camcorders? They sound like the most comfortable and easiest way to record videos, with straps and everything. They were compact, portable, and wasn't heavy as all heck

Smartphones happened.

[–] [email protected] 2 points 1 day ago

sad. now we use RECTANGLES to record funny videos instead of cylinders.

[–] [email protected] 11 points 2 days ago (2 children)

If they keep being rotated they wear out easily.

[–] [email protected] 7 points 2 days ago

fair point, makes sense

[–] [email protected] 5 points 2 days ago

Can confirm. I used to fidget with the charger on an old laptop of mine by just spinning it in place in the port. Over time, it loosened up the connections to the point where I had to duct tape the plug into the port.

[–] [email protected] 7 points 2 days ago (5 children)

Because of all the pins involved with USB, I think these would end up bring more like the mouse plugs of yore. USB C seem pretty awesome to me for this scenario.

As for a "wall" plug, given the voltage there, maybe there are technical challenges with safety? This is an interesting thought to me, i haven't really thought much about wall plugs haha. There is so much room for improvement in my country (USA).

[–] [email protected] 3 points 2 days ago (6 children)

those old ps/2 mice and keyboard plugs were annoying as hell. definitely not designed to be easily hot-swapped.

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[–] [email protected] 2 points 1 day ago

I ate them

[–] [email protected] 3 points 1 day ago (1 children)

It is my understanding that Apple actually wanted to use 3.5mm jacks for their ADB keyboard/mouse interface in the early days, and some prototypes exist which used the jacks.

https://www.applefritter.com/node/294

The plug manufacturers couldn’t guarantee that you wouldn’t sometimes get high resistance issues if the plugs were left connected all the time. On a pair of headphones you’d hear that as static and turn the plug or unplug/insert to get it going again. But you can’t “hear” through a keyboard.

They used mini DIN 4 instead.

[–] [email protected] 1 points 1 day ago

oh i didn’t know that apple wanted to use audio kacks for keyboards and mice, i only thought it was some of the ipods

[–] [email protected] 3 points 2 days ago* (last edited 2 days ago) (1 children)

There is a lot more information being handed back and forth between the thing giving power and the thing getting power than we used to rely upon. Its not that cylindrical plugs couldn't be done, but they would probably need to be much larger than is strictly necessary. The jacks would be necessarily larger to accommodate.

Old barrel jack type equipment is incredibly dumb, as in it has very little information passing back and forth.

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[–] [email protected] 3 points 2 days ago

another downside to cylindrical usb plugs would probably be thinness, USB-C ports are quite a bit flatter and suits thinner devices a lot more

[–] [email protected] 3 points 2 days ago (3 children)

Why does the majority of your post read like you don't know these exist? https://en.wikipedia.org/wiki/Coaxial_power_connector

They're fine, but as you mentioned in the first paragraph, lack of a standard is their main drawback. You could find two power supplies with the exact same connector but different voltage and polarity.

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[–] [email protected] 2 points 2 days ago* (last edited 2 days ago)

Telephones in Germany had round plugs until after ww2. The plugs were very convenient and also very bulky. They got replaced with much smaller plugs with more pins.

[–] [email protected] 2 points 2 days ago

Of course there are:

[–] [email protected] 2 points 2 days ago (1 children)

For certain high voltage applications , like public PA systems, 1kw+ light and lasers, there are a still cylindrical plugs pug they use pins a bit like the old ps/2 port

[–] [email protected] 1 points 1 day ago

Amphenol connectors. Used a ton in industry, military and aerospace. They are actually really nice when you get down to it, but you need expensive tools and the connectors themselves are usually quite expensive. I once had a client ask for a specific 6 pin one, only about the size of my thumb, it was $800.

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