whats old is new again, I remember 'ergo' point-of-sale KBs from the early 80s that were joined via the same method.

it's a good reliable plug if you can cram what you need through it, I can kind of understand why people gravitate towards it in design.

4-pin mini-din and reusing s-video cables is a much better proposition, and how logitech tend to do things.

USB is usually too complex for something like a simple split keyboard; the TRRS runs I2C with sth like a MCP23018-E/SP IO expander in the other half.

You can use a physical connector without using the standard protocol.

Most split keyboards these days have a microcontroller in each half. IO expanders like the MCP23017/MCP23018 are fairly expensive, quite slow when used with microcontrollers like the ever-popular Pro Micro's ATmega32u4, and they really limit your hardware options on the secondary side.

It usually makes more sense to just stick a Pro Micro on each side, and have them talk serial over TRRS. As a bonus, you can connect it to your PC from either half.

Offtopic:

Recently I found myself in the market for a custom keyboard, to my great surprise. Custom as not as DIY but as something different than $10 OTC or even $100 Logitech.

After the hours of watching pics I decided to just see it with my own hands and went to a shop which specialize on them.

And there I confirmed the feeling what I had before - 99% of these keyboards, despite quite advanced tech gone into them on all layers, are not usable, because they are made to stroke the ego of the owner but not for the actual work. This is especially evident by the crammed right cluster which makes typing brackets, curlies and quotes quite a pain, because the Shift key is gutted and nowhere under the right pinky.

Using something else than microUSB or Type-C (for the PC connector) is just a cherry on top.

You seem to be in need of not a keyboard customized for you, while judging keyboards customized for others' needs.

Come up with your own layout and get that custom design made.

> You seem to be in need of not a keyboard customized for you, while judging keyboards customized for others' needs.

Ah, yes, just searching for the wide RShift, on the place where it was for the last 30 years is 'customized for me'. K TNX

Thumb shift is better anyway...

"You are pressing your shift wrong" Steve Jo^W^W CarVac, 2024

They use USB-C to the host, the TRRS simply communicates the two halves of the split between each other. You don't plug the keyboard into the 3.5mm jack on your PC!

You could just get a custom keyboard that is comfortable for you. Key mapping is generally an independent step. Most of these keyboards are completely programmable with custom keymaps and layers. Many come with blank keycap options, you can also rearrange a regular keycap set.

You can't do what OP is looking for without a custom PCB. The switches and caps and mappings might be customizable but their physical position and size on the board isn't.

Despite pushing the envelope in many ways, custom keyboards can also be strangely traditionalist at the same time. Making a PCB is a risky venture and most manufacturers don't want to risk it.

A huge amount of models still use a huge 7u or larger space bar for example when something as small as 4u would suffice, and leave room for much more ergonomic placement of modifiers. (or other improvements like extra keys, keyed gaps etc.)

Yes, most keyboards still have the traditional layout. But I believe many options fit what OP needs. A split keyboard such as Ergodox EZ allows access to the maximum amount of keys possible without moving your hand. You can then customize the mapping to properly distribute commonly used keys.

Ergodox EZ is ortholinear. Ortholinears by their nature tend to not have spacing issues but they require (extensive) retraining.

There's a very good chance that the above poster was looking at staggered layouts if it's their first foray into custom keyboards, and not even considering orthos.

While it is quite popular, TRRS is one of the worst connectors possible for a power rail (eg usb VBUS) because it all but guarantees that VBUS will be shorted to ground if you ever accidentally hot-plug it.

VCC is on the sleeve, last to enter the jack, GND is a ring deeper inside the jack. It's not clear to me how VCC would ever get grounded unless you pushed the connector in too far somehow.

There is a note about a diode across VCC and GND — perhaps that is to prevent this kind of short?

Think about unplugging from the side thats _delivering_ the power. As you pull it out, the GND (which is further in and needs to travel out as it's unplugged) will contact the live VCC.

Even from the power consumer side, there is a chance that a single female side contact (eg VCC) may touch two adjacent TRRS sections as the plug is being removed.

Also, 3.5mm jacks and plugs WILL suffer oxidation problems from using them for power.

Isn't solving this as easy as just not having VCC + GND on the pins next to each other?

If you shove data in the middle, you're never going to short VCC + GND together. your data line shouldn't care about being high (5v) or low (gnd).

No so, even if VCC and GND are on opposite ends of the TRRS, they will pass by eachother as the cable is unplugged.

No, that's not how that works. If tip is ground and ring is Vcc, there is no possible way to create a dangerous short.

So lets imagine what happens to the host port when you unplug a live device. Vcc breaks first, and all other pins shift. D+ and D- are safe to short together or to ground (and I'm pretty sure safe to short to Vcc) so they don't matter much. The shield is physically out of the socket. As the connectors move, you get connections that put Vcc on the device's Data pins, through the device ground to host Data pins. This is equivalent to a large resistor between host Vcc and data pins, which is safe.

As the connector is removed, the device's ground contacts host's Vcc. Nothing happens because all the other pins are physically outside of the socket. There is no circuit, no path for the current to go. The only way it could be a problem is if the device had some external ground connection. That would create a direct short between the host's Vcc and ground.

But (correctly implemented) USB ports can safely tolerate a short from Vcc to ground. If not, it's not complicated or expensive to build protection into the device.

Even if all of the above weren't true, it's still not complicated or expensive to design a port which is tolerant to any kind of short on any pins.

What you're arguing is both not possible and wouldn't be a problem even if it were.

also could use the switch built into the phone socket that only connects power wires when the plug is fully inserted.

There are ways to handle it. For example, before it is firmly plugged you can just sense what is happening -- us minimum voltage and high impedance to prevent sparking and to get information about the state of the mating.

You only turn on actual power when it is firmly connected and you turn it off immediately when there is any signal that it might be disconnecting.

The trick is doing so in a way which requires basically zero hardware. DIY ergo keyboards are built around a controller like the Pro Micro - which can't do this out-of-the-box.

Having to add a bunch of components to implement such a feature isn't really worth it when switching to USB-C also solves the problem, at basically zero cost and effort. It's not spec-compliant of course, but who cares with DIY?

Perhaps one of these trs plugs that has a spring-loaded ground sleeve? https://www.neutrik.com/en/neutrik/products/plugs-jacks/plug...

This unfortunately isn't a new thing for experienced users, it's a relatively well known "issue"