One is Read Only Memory, the other is Write Only Memory (the holy grail)

Firstly, reversible plugs are harder to make structurally resilient, they only become feasible cost-wise as stronger materials become cheaper and manufacturing grows more efficient.

Secondly, reversible plugs are a lot more complex. Compare the 4(ish) pins of USB-A to the 24 pins on USB-C. Not all of them are strictly necessary for parity with USB-A, but you could cut that number in half quite easily if the plug were not reversible! Sure, this complexity impacts manufacturing, but, less obviously, it also pushes that increased complexity onto the USB controller hardware/firmware.

Neither of these issues were necessarily dealbreakers, but... for a long time they certainly did conspire to make reversible plugs into a pipedream. I have to imagine that were always bigger problems to solve and fewer resources to work with! We're just now seeing reversible plugs really take off because we've finally crossed that magic threshold where it makes sense to try surmounting those barriers.

Meanwhile we were connecting printers, scanners, and other peripherals using a 25-pin parallel (or sometimes SCSI) plug. Granted, the DB-25 was already pretty old at that point, but I have to imagine a 24-pin reversible USB plug would have been close to that size if it had been developed in the 90s.

The physical design of FireWire was one of its many advantages, in that you could instantly tell, visually and by touch, which side was up by the beveled corners on one side of the plug. I’m guessing the answer here was again cost, that manufacturing an interconnect with two 90-degree angles and four 45-degree angles was more expensive than one with four 90-degree angles, but I’ve never seen any confirmation of this.

The sole reason as stated by Ajay Bhatt, the project lead at Intel, was cost. They wanted to encourage mass adoption of USB and every cent saved helped in that initiative.

The compromise for UX was to make the connector rectangular rather than circular, so that there was a 50% chance of getting it correctly orientated on first try.

I never ended up getting a camera or anything else that supported FW, but USB always seemed to work well enough for my (relatively light) use case.

Fun fact: USB 2 Mini/Micro connectors actually have 5 pins (hence my original 4-ish statement). The 5th pin doesn't actually go over the wire, it's just used as a signalling pin to the controller that tells it if the plugged in device is compatible with USB OTG.

Not precisely. The type C connector has four distinct USBSS pairs; the type A connector only has two. This allows the type C connector to be used to carry DisplayPort or other high-speed data alongside USB.

[0] https://upload.wikimedia.org/wikipedia/commons/thumb/0/07/US...

I'm fairly certain they are using double the number of USBSS because they're available due to the mirroring. It was the easiest way. Unlike the control channel or side band, you can actually benefit from using all the pairs for data transmission since they're already there.

Lots of cool applications using that technique.

This is misleading.

If you want to only cover the USB-A spec with USB-C, you need only 8 pins.

I have a cheap USB C on my desk that got 8pins because it do only USB and charge.

USB-C can pass HDMI signal on the other pins, which your USB-A can't do.

> Not all of them are strictly necessary for parity with USB-A, but you could cut that number in half quite easily if the plug were not reversible

Is 4 not half of 8?

Also: USB-B micro connectors might have 5 pins, but the cable itself has 4 wires. The OTG pin is grounded in the connector. This is actually why I said "4(ish)" in my original post.

Thats why USB-C have more or less the same speeds than HDMI, while the HDMI have 22 connectors.

Compare what is comparable, you can't use your USB-A to display 4K-60Hz video, but you can with your USB-C, or HDMI.

I used them for plugging into public power supplies, but they were never sold to consumers labeled for that purpose.

A one-way plug would be fine if the profile were sharply asymmetrical, to the point where one could find the right orientation by touch alone. Maybe something like an even more pronounced trapezoid than hdmi.

Though, in all seriousness, it would make an interesting security through obscurity feature. Everything works fine with the device, but only allows/shows certain features/files after Satan's rotation pattern. More secret squirrel than "security" in reality.

You and everyone else.

I knew this was not going to be ideal in the late '90's when USB 1 came out.

Radio Shack was still going strong but this was the first PC connector that you could not purchase plugs or jacks for to solder your own. Also no suitable 4-conductor cable.

Even though the USB 1 approach was for a 92 foot maximum cable length (since it was only intended for the low-bandwidth webcams at the time) this was rapdily nonpublicized since USB 2 was already in planning, for much faster speed and a 25 foot max cable length, eventually shortened to 16 feet.

Well once you got suitable cable, you still had to cut pigtails off of USB cords so you could get the cable ends.

https://chromium.googlesource.com/chromiumos/third_party/hdc...

(but that's with a special cable)

As in, someone got a new mouse and didn't know where to plug it into their computer, when in fact there was only one DB-9 connector on the computer where it will physically fit and it would be the correct one.

USB 3 introduced blue plugs, complicating things slightly but still everything basically worked, and if something was operating slower than expected it was at least obvious by the color.

Then 3.1 and USB-C came out, and apparently USB-IF lots its collective mind. Now you have you pay attention to see if your ports, cables and devices are "USB 3.0" or "USB 3.1 gen 1" or "USB 3.2 Gen 1" or "Superspeed" or "Superspeed 5Gbps".. (Btw, trick question: all of those are the same thing).

But yes, I agree the USB-C plug mess is probably the worst. It has became worse than what it "wanted" to solve. The only way to make it work as broadly advertised again would be if all plugs supported all protocols (that make sense for a given device) and PD options, etc. on all devices and with common cables, at max bandwidth everywhere, but not only I'm not sure this is technically possible, this would probably be cost prohibitive.

And so what is the point? The net number of ports decreases on laptops, and there is no need on most gadget devices (beyond data+PD). The only point is for manufacturers to economize 50 cts and make the new inferior laptops pass as better than the old ones because they use the shinny new USB-C plugs. I would be happy if the price was actually 1/2 of the old models.

The Tektronics TDS-4xx oscilloscopes produced VGA-signals-on-EGA-pinout, for one example I've encountered in the wild.

DE9 connectors were also used for RS232C serial ports, which included mice and modems and all manner of other things speaking RS232. Wand-style barcode scanners were quite frequently on a DE9 connector, speaking some obscure protocol which may be at RS232C-compatible voltages but probably had positively Martian numbers of data/stop bits, etc. Or maybe just a raw photodiode signal so plugging into a serial port wouldn't do anything useful at all. Heaven help you.

Beyond that they were also used on Token Ring network cards (the hermaphroditic connector being to large to fit on a slot bracket), Fibre Channel in its copper variant (using the same pinout as Token ring, thank goodness they wouldn't blow each other up if mistaken), and pretty much anything else that only needed a few signals. It's a durable, ubiquitous, easy-to-work-with connector.

And of course in industry, the DE9 connector is still used for a zillion more things, like CAN. Pretty much every CAN test tool you'll find uses pins 2 and 7 for CANL and CANH respectively, with 3 and 5 as ground.

Pin 9 has quietly emerged as a sort of de facto phantom power supply, and if you stick 9-to-12-ish volts on it with a polyfuse, a lot of devices will run from that and not need batteries. Some RS232 GPS receivers would accept that, and the Toughbooks with serial ports still produce it.

Here's a funny: RS232 on DE9 is still produced today by the millions, on the backs of fancy TVs, because it's still the most sensible way to interface with high-end home automation systems. (USB never arrived at a good way to do peer-to-peer, and requires entirely too much software.) It's a 60-year-old standard and still has legs.

This is already a solved problem[1] through color coding. Not sure why they couldn't use that scheme. Maybe combine a few to indicate things like DisplayPort and Thunderbolt capability, could have up to four quadrants for example.

[1]: https://en.wikipedia.org/wiki/PC_System_Design_Guide#Color-c...

Speaking from experience, I don't think most end users are liable to pay enough attention to their ports to notice the color coding. I remember family members being confused by the blue 3.0 ports when those were a thing--now there's also red ones, and different color C ones, and some C ports have the little lightning bolt and some don't, and most users don't know what THAT means.

The value-add of USB C was supposedly you didn't have to buy different cables for different purposes now, you could just slap everything on a C port. But of course that's not truly the case, and we're now in a messy soup of standards and capabilities that even to seasoned tech professionals are hard to disentangle, much less for end users.

Calling this a solved problem 'cuz they slapped some colors on some of the ports is missing the forest for the trees.

I doubt I'll ever plug anything but a smart phone into it, but it seemed worth it for the feng shui.

You would think so, but no. Colors don't help.

Not just because a good chunk of the population has color vision issues. But people for some reason the average person can't latch onto that sort of thinking.

We went through this back in the 90's. Your PS/2 mouse plug was one color, and the PS/2 keyboard plug was another color. But people still tried to stick them in the wrong places.

Same with the sound card. Microphone, speakers, line in, line out, all had their own colors that matched the wires that came in the box. Regular people screwed that up all the time.

Going further back to the 70's and 80's, if you looked at the back of anyone's rack system, there was a 50% chance they had the red/white pairs of RCA plug backwards. Then when video started getting carried over the same plug, but colored yellow, things got worse.

Maybe if the next standard has colours to start with, and they are unambiguous, and somehow not even ambiguous if confused with a previous port version, and they are adhered to by all manufactures, consistently, and nothing new arrives that someone adds a colour for before the standards body makes a decision...

But it's still costly at the start of the refinement cycle, and it's hard to bootstrap without allowing manufacturers to do cheaper cut down feature versions to get the ball rolling. It needs to provide some marginal value in the mean time and real promise, even if it means some higher overhead in the establishment phase. So for someone buying a new device in 2025 or 2030, USB-C may still exist but I think issues with what ports do what will be lessened. We already see devices like Macbook Pros where all the USB-C ports are functional, and while those are on the higher end of pricing they aren't stratospheric enterprise territory either. I suspect it won't take that many hardware generations for that sort of thing to spread downward. The question is if that's worth the immediate trouble.

And at least for USB-C, I personally think it'll be worth it. It's a good connector, and the improved capabilities are valuable. We've had USB-A for a long, long time, and it doesn't seem unreasonable to guess that USB-C will stick around similarly. There was demand for something more compact and reversible with other QoL benefits along for the ride, and I think it's worth the upfront cost to get the whole industry onboard something that can converge rather then ending up with various manufacturers going their own routes.

My phone barely charges at this point, which is frustrating because it otherwise performs fine. I'm going to have to buy a new phone because of the damn charging port!

I was considering how many times I've actually plugged it in. Worst case for me would be 3x/day. At 3 years, that's only ~3300 times. Surely they stress tested the connection more than that before production? Of course, these days I'm plugging it like 20x/day because it falls out or just doesn't work.

I don't even bother turning my phone off, but it's rated as water resistant and so I am pretty confident that there aren't any voltages present when disconnected. Even on non-waterproof phones, though, any voltage persistently applied to pins on an external connector will result in corrosion over time, so it shouldn't be a problem to just mechanically scrape gently with a dry metal needle.

You could geek out and learn the difference of upstream (A, host) and downstream (B, device) ports, the various types of B port sizes, and that was it. Later USB 2.0 was introduced and just (bam!) made it all 40 times faster, but it still logically worked pretty much the same.

Then USB 3.x came and just blew all that to h-ll, which is frustrating for both old bearded geeks, and* new/non-technical users.

Except that my desk has three USB cords, each with a color-coded label so that I can tell what each one is for. One is seemingly the only one that will charge my e-reader, but only does low speed data transmission so it never really gets used for anything but my e-reader. Another is power only and therefore useful for charging devices without my computer attempting to talk to them. And a third is a proper, modern (ish, I suppose), well-behaved USB 2.0 cable.

You do see NEMA 5-15R receptacles on 20A circuits in residential applications, but that's probably because most appliances don't require 20 amps. A 5-15 connector has two vertical prongs, a 5-20 has a horizontal and a vertical, with the special case of receptacles with a T slot that fits both 5-15 and 5-20 plugs.

It goes a bit deeper than that though: A NEMA 6-20 also has a horizontal and vertical prong, but they're reversed from a 5-20 so you can't plug them in in an incompatible (and likely hazardous) way.

The whole standard is really well thought out. I went down the rabbit hole when I got an old table saw with a 6-20 plug and had to figure out what the hell to plug it in to (dryer outlet, via a "custom" extension cord).

I feel like I haven't seen too many uses of Schrader valves that are likely to cause havoc. Most of the use cases for them besides tires are pretty obviously special and distinct from one another. I mean, I'd hope nobody's ever hooked a bike pump up to their air conditioner or a can of R134a to a tire...

This is, of course, what I was talking about. I do appreciate the nuances of the 15/20 T-socket and the 6-20/5-20 symmetry; NEMA is super cool (aside from the fact that bladed plugs that aren't twist-lock are sort of lame/less safe in general, at least compared to the UK standard bladed plug). It's a fun rabbit hole to venture down: my occasion was having to adapt straight-blade wall box receptacles that the electrician installed to the twist-lock of the PDUs we had bought.

There's also a fun and confusing mess of competing DC connector standards. I haven't decided what 12/48VDC connectors I'm going to put into my new house build yet (beyond the obviously mandatory 5V USB).

Stupid question: are there any common household appliances that draw 20A? I've only ever seen the T receptacles in non-household uses.

FWIW if the nameplate of the motor specifies current draw at 120V, you can likely reconfigure the motor to use 120V instead of 240V.

[0] take a look at the gauge of a dryer's internal wiring, which is regulated by UL/CE and not NEC.

Rewiring the motor to 115v is probably a no-go, since it's a 3hp motor (continuous), which I believe is more amps at 120v than could be drawn from a normal circuit.

For safety, I'm wondering what kind of faults wouldn't be protected against. The starter has built-in thermal protection (heaters), which should protect the motor from the unlikely use case where I'm pushing the saw too hard, or more likely, a stall on start-up.

The breaker should still protect against shorts. I'm not knowledgeable enough to know what other faults could lead to an over current fault that one or the other of those wouldn't catch.

Would anybody care to educate me?

Also: the most dangerous aspect of a table saw is probably not the potential for electrical faults :-)

I'm having a hard time coming up with a compelling failure mode, given that thermal protector. Perhaps when the rotor locks, the thermal protector has a slower curve than the saw's wiring (which is assumed to be protected by the circuit breaker's curve). I would hope the saw wiring would be a bit oversized such that it too was protected by the motor thermal protection, but without doing an engineering analysis of the saw itself, you don't really know.

Unknown unknowns are my real point though - you're operating outside of the electrical code. Same as if you wired up a workbench of 5-15 receptacles with 10ga and put a 30A breaker on it - realistically it's going to be fine, but we avoid doing this. All those different NEMA plug sizes exist for a reason. 5-15/5-20 is really an anomaly where you can plug the smaller into the bigger, and even there I've got to wonder if eg old table lamps on a nice stiff 20A circuit are a good idea, or if they just haven't been focused on because they're statistically unimportant (see also: strings of Christmas lights with receptacles at the end).

FWIW I'd probably do the same thing you did, but at the cost of making sure I unplugged the saw whenever I was done using it until I made a proper permanent circuit. But that is not professional advice!

Before: "Here in the back of the computer we have PS/2 ports (1 for keyboard and 1 for mouse), a parallel port, serial, 25-pin serial, game port".

Introducing USB: "Everything is USB now! Plug anything anywhere!"

USB version whatever: "Well the sockets look all the same, but you can only plug your display in here, to charge it you have to connect it here", etc, etc.

With USB-A and -B, there is a physical indication of the direction of flow (data and/or current). Just "connecting" two things is sometimes unambiguous, but sometimes it's not.

You mean that one can hold 15A and the other - 20A? If so, they do work the same, they just have different capacities (like a tap, some of them will provide more water, others less but they work the same (especially if they look the same))

Some USB-C ports have DisplayPort output, so there's a DP near them. Some do Power Delivery, so there's a battery near them. And some are also a power input to the laptop, so there might be other random symbols near them.

It's chaos. I just juggle plugs until I get the expected behavior, and sometimes I never do because it's not implemented. I've given up.

Edit: as long as you're not using a needle-like piece of metal to dig at or bend the contacts, it should be fine.

Now there are 4 combinations to try rather than two (flipping each end of the cable - 2x2 = 4)

I also found a laptop power supply that would cause the CPU of whatever machine it was plugged into to run at 100MHz. That was a fun one to troubleshoot.

The unfortunate thing is that Thunderbolt was created, and instead of a simple way to make PCIe external, we have this Intel-created mess that tunnels PCIe over some cursed "MPLS-like network" or whatever it is. And it was completely Intel-proprietary until recently. At least now the spec is open.

We should have different connectors for different data rates and power levels. Don't pass the buck to designers, they'll screw up.

Ok, sarcasm aside. Technicaly you dont need separate plugs for different connection levels and power transmission up to certain powers. Initial data exchange at some base speed and minimum power requirements can provide necesarry information for devices to establish or refuse connection

And it's still only useful for low power devices.

I've never gotten a real answer, one that involves technical reasons. It could be done, but it isn't.

I guess people like having different kinds of cables?

Or doesn't the stub matter for signal integrity / EMI because it's only a couple of mm and fully enclosed by the shield of the plug and the receptacle?

This doesn't work for the super-speed differential pairs because they're actually different lanes.

I have a Lumia 950 (one of the first USB-C phones) and a short USB-A to USB-C (or apple) cable/adapter.

One orientation does not charge the phone, so hes right it does happen.

They only do that in this combination. Not sure if it's consistent though - I should probably mark one side and check.

[1] Like this: https://imgflip.com/memetemplate/153127632/Cross-fingers

Hm HTTP 451, or JS error?