TRRS Jack Confusion

[noteveneric]

So I'm planning a handwired build for the first time apart from macropads and wanted to know things. I want to make a 65% with the top row being detachable- see my beautiful MS paint diagram below.

Since the num row will be separate from the rest of the board, would I be able to wire a TRRS jack to power it? I assume I'd need an extra Pro Micro / Teensy (which would be better?) but how could I power it? Would TRRS be the best choice? Is this project even possible? Thanks.

[piit79]

TRRS jack is used in nearly every split board I've seen, so it's definitely a good choice. It carries up to 4 signals - that would be your Vcc, GND and TX/RX (if using serial) or SDA/SCL (if using I2C).

Teensy is a modern 32bit alternative, but quite a bit more expensive, so I'd probably stick with a Pro Micro. (There's also the cheap generic "Blue Pill" STM32F103 board that's 32bit ARM, but I think it would be unnecessary large physically.)

For the above, you can draw inspiration from some open-source split boards, e.g. Corne/Helidox/Crkbd.

How are you going to attach the num row to the rest of the board? If you managed a secure connection using strong magnets and wired the num row in a clever matrix, e.g. 3x5 or 4x4 to require just 8 connections, I can imagine you could add spring-loaded contacts on the side of the num row that would attach it directly to the main board and do away with the complications of split board completely.

[noteveneric]

Yeah so that's the thing. The purpose of the board is to primarily be a build without the numrow but I wanted the numrow exclusively for games and I wanted to not take it everywhere. It's extra, yeah, but I think it would be interesting. The problem is that I now have to basically build two different sandwich cases and wire pretty much two different keyboards.

[piit79]

If you're planning to create a sandwich case I think the idea of attaching the num row directly to the matrix would be hard to pull off - but not that hard if you were able to 3D print a mid layer. Then you would do away with the second micro and TRRS connection.

Anyway, definitely an interesting project, do keep us updated with your progress!

[noteveneric]

If you're planning to create a sandwich case I think the idea of attaching the num row directly to the matrix would be hard to pull off - but not that hard if you were able to 3D print a mid layer. Then you would do away with the second micro and TRRS connection.

Anyway, definitely an interesting project, do keep us updated with your progress!

Can you elaborate more on this midlayer? How would the wiring be different? The goal is for it to be completely detachable: couldn't the second pro micro act like a numberpad? How would you skip that with a mid layer? Thanks!

[piit79]

Sorry, I see I didn't make myself clear - or perhaps I didn't understand your requiremens clearly. I understand you want to make the number row fully detachable - does it mean you want to be able to position it away from the main board when using it? I assumed you wanted to detach it when not using it and attach it to the board in the normal layout as the top board when in use.

My solution would involve a sort of pogo pins/spring loaded contacts in the mid layer that would connect the number row to the main controller when attached to the top of the board (maybe with strong magnets). The number row itself would be "dumb" - it would only contain wiring (in a virtual matrix to keep the number of connections down), no microcontroller.

If you wanted to be able to use the number row in a detached position, my simplified(? solution would still work if you connected it with an 8-wire ribbon cable with a 2x4 pin IDC connector: https://images.app.goo.gl/mbsmBj8QGSPTsJyE6

[noteveneric]

I guess I want your first idea the most: detachable when it’s not in use. Having it be detachable AND functional isn’t worth if it makes it wickedly overcomplicated. I want to be able to take off the number row when I don’t want to use it, and set it aside for whenever I’ve gotta type numbers often. It can just be a plate with switches and stuff when it’s detached, but when it’s attached, I could plug in a cable and make it functional. Does that make sense?

[pabile]

oh! cool ideas from both of you!

i think some approaches made by http://www.40percent.club/ may be useful. he have several modular PCBs that i think does not fall far from what you have in mind.

[tinyenormous]

I just learned that trrs cables are not hot-pluggable. so if you went that route you would have to unplug the main usb, then separate the trrs cable, replug the usb, and carry on with your day. The trrs plug contains power and it can hit against the other pins when plugging it in.

*one interesting thing about your project is that you could end up with one male and one female port. ie no cable. That (I believe) would fix the hot-pluggable issue if you wired it the right way.