Please help to draw a schematics for cherry ML based keyboard.

[Nylithius]

Disclaimer: sorry if i put this topic in wrong forum, move it to more convenient forum if it require.

Hello forum. Currently i'm working on yet another ergonomic keyboard, which is not announced yet. And i need to draw a schematics for my circuit boards (4 circuit boards total). And here i require your help.

Everything else is just fine: i know well C programming language, i can use "tmk_keyboard", 3D model of my keyboard is prepared to be printed, etc. Except one this simple thing - electronics. In particular - PCB circuit scheme.

Sadly, this is my first project which require PCB, and at least basic knowledge of electronics. I ofc. know how electronics and mechanical keyboards work, but i have no experience of drawing PCBs.

I will use cherry ML switches, and AVR-USB162MU (or it's analogue) as a controller.

But i currently stuck on PCB drawing because i have no idea how to draw it.

Here is example of PCB of cherry ML based keyboard:


And here is example of scheme of approximately similar keyboard (sorry - scheme is transparent):


So here i require your help:

1) Do any of you know how i should connect switchers to controller? Especially cherry ML and AVR controllers.

2) What i should know before i attempt to draw nice scheme, and what i should do before that?

3) Is cherry MX similar to cherry ML? Can i use MX-based scheme to draw my own? (with modifications ofc.)

And yes, here is small picture of Cherry ML's pins:

Hopefully this will help you help me.

I will tell a bit more about my keyboard in different topic, right after i'll assemble it, but here is basic layout of my keyboard:


That's why i need 4 PCBs to get it done. It's divided by 2 parts, and each part have "main frame" with all basic keys, and "thumb frame", with 4 thumb keys.

[Lanx]

**** cherry ml, ml is like the ghetto poor version of mx, i use a ml for my htpc for years, they suck compared to mx. Mx do not have the pins of mls.

[kurplop]

I'll be following your progress on your ergo board. I've been working on a similar design using alps switches but I became curious about the ML switch, particularly for a small, tented but collapsable, ergo travel board.

I picked up a used CherryML board off ebay for $15 to check out the switches. Not as nice as MX's but not bad in my opinion. It  seems like a good way to have a mechanical keyboard that isn't overly bulky. I was surprised to see the 4 leads per switch. Duplicates I presume, as your a,b, designations suggest.

Sorry I have no answers to your questions; I've been tempted to ask the same ones.

[HoffmanMyster]

I think Making Stuff Together is a much more appropriate location for this.   

Good luck with the project, and hopefully someone can help you out!   

[OldDataHands]

You should start with hand-wiring a plate-mounted, MX-switch keyboard with no PCB.
See here for examples: http://geekhack.org/index.php?topic=40567.0

(Can ML switches be plate mounted? If so, then you could do ML instead)

After you're happy with your hand-wired circuit and have finalized your physical layout,
and only at that point, should you make a PCB. When you get to that point, use KICAD
and follow as many tutorials as needed to get the feel of it.

Good Luck!

[Oobly]

What OldDataHands said.

Reasons:
1. MX switches are more common in DIY projects and you can find layouts, dimensions and existing board designs more easily.
2. They use 14mmx14mm square holes for plate mounting and can be mounted in any orientation, so you have more flexibility with your PCB layouts, whereas ML switches have different X and Y dimensions and have to be mounted the way you have designed the plate.
3. MX switches have much better options for keycaps than ML.
4. With MX switches you can change the switch type (tactile, clicky, smooth, hard or soft springs) and offer more options to the customer without changing your design.

4. You can prototype your design quite easily with hand wiring the switch / diode matrix and a controller (for the first prototype you can use something like a Teensy and use existing firmware). You can then change the controller easily to the one you want to use for production (possibly with a breakout board) and continue testing the firmware with the same prototype keyboard. This allows you to use a single prototype to test physical layout, wiring (row or column driven), different controllers and different firmwares to help finalise your design.

5. KICAD is fairly easy to learn, there are tutorials for it and quite a few members of GH use it and could give advice if needed. Once you know your design electrically, making the PCB layout is relatively easy (although there are a few things specific to PCB's to be aware of, such as running ground lines between sensitive data lines, etc.)

Regack is a GH member who does great work on PCB designs, so it may be worth approaching him at that stage of your project, whether for advice or help with the actual layout. Not sure about possible commercial designs (he may not want to do those), but he has helped out with a few community design projects.

Good luck with the first build! Looking forward to the build thread.

[jacobolus]

(Can ML switches be plate mounted? If so, then you could do ML instead)

No. But I think you might be able to just drill little holes in a thin piece of wood or acrylic or something, and possibly glue the switches down to get them to stay in place.

It’s possible to find some ML laptop replacement boards very cheap on ebay (<$20 shipped), to harvest switches from, so I don’t think it really hurts much to use glue for making a prototype.

[sth]

ML switches are pretty hard to press and really prone to friction unless they're lubed. not sure if i would consider them to be particularly ergonomic, but a good starting place if you have access to a lot of ML boards/switches for donors.

[jacobolus]

I’m curious whether keycaps could be made for ML switches which had an even smaller top surface than the typical keycap (maybe even of a circular shape), so that they couldn’t be pressed in a corner and bind up.

On the subject of glue, perhaps it would just be possible to glue something like a sew-through button to the ML slider, as the keycap.

[One other thing: the large stabilized ML keys seem completely fine to press anywhere on their top surface, as the stabilizer prevents them from tilting.]

[suka]

(Can ML switches be plate mounted? If so, then you could do ML instead)

Yes, technically it is possible to achieve enough friction with a rectangular shape and holes for the pins, but from my experience the margin of error between too loose and so tight the switch will no longer return when pressed is pretty thin with these switches. But it worked on my earliest prototypes:



While I personally do still like the ML switches (especially for their low height in custom builds) and cannot understand all the nagging about scratchiness I'd also recommend to use MX switches instead for all the reasons already mentioned: Simple and reliable plate construction, availability of switches and caps.

[Nylithius]

Hello forum. Thanks for all your suggestions here, and i can say agree with them.
I mean - your words about MX switches. And i will use MX Clear probably on future projects, but it's not final decision.

About ml: i choose them for first project only because they low profile and has low travel.
For this project i will keep on ML, just for an experiment.

I kinda figured out what i should do, and here is picture of what i should do:


Simply connect B, A', B' together and put diode from A to ROW.

Or it's bad scheme? Can you tell me?

Also, dear suka, can you show me how you did the schematics? And how did you connected swithers' pins? And one last thing: did u used diodes? Or switches have diodes on their own?

[sth]

I’m curious whether keycaps could be made for ML switches which had an even smaller top surface than the typical keycap (maybe even of a circular shape), so that they couldn’t be pressed in a corner and bind up.

i think SP might already have a mold for something close to that.

[suka]

Also, dear suka, can you show me how you did the schematics? And how did you connected swithers' pins? And one last thing: did u used diodes? Or switches have diodes on their own?

Don't want to sound rude, but everything is visible in the picture above:
IIRC, the switch contacts are a and a' in your earlier picture while b and b' is merely a bridge which could be used for cleaner routing, or in my case as a separate connector of the diodes. Where you put your diodes is more or less up to you but will have to match your firmware.

[Nylithius]

Ok, sorry that i have not payed enough attention.
I'm just COMPLETE newbie in all this so... yeah... sometimes i sound ridiculous 

[Nylithius]

Ok, here is my final scheme. What forum can say about it?


And yes, controller is AVR-USB32U4, it's clone of Teensy 2.0

[erbay]

Nylithius, the keyboard design that you have proposed is a very interesting one. I’d perhaps like to get my hands on it one day. Now about designing electronic circuits, it is important to use correct type of switches in such circuits because these are the most important components. Anyways, after you’re done with it, do let us know how the circuit feels and works.

[tlem]

You can remove the resistors in each column.