Author Topic: A Compact SSK Model F  (Read 5789 times)

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Offline wcass

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A Compact SSK Model F
« on: Thu, 21 June 2018, 18:47:05 »
Two and a half years ago, I replied to the “post your ideal keyboard layout” thread with this:
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A couple of months ago, I decided to make a CSSK and document how I did it for anyone interested in making a custom Model F. This is that.
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I decided to go with a “layered case” design because it is simple and inexpensive to prototype. It also let me experiment with the idea of a “Flat F” (or F ) an idea floated a while back by my friend Lot Lizard. Without a curved back plate, the gap between rows of key caps is wider, so I would want to compensate for that.

 
Another thing I wanted to do was to reduce or eliminate the border around the keyboard edge. All previous Model F pad cards (the PCB with the capacitive pads) have rows that gather at one side and route to the controller, and columns that gather at the top and route to the controller. This dictates a need for a border on at least two sides. I wanted to try making my pad card from 4 layer PCB which would allow me to place rows on layer 1, columns on layer 2, use layer 3 as a shield, and run traces to the controller on the bottom – thus eliminating a need for much of a border. This also significantly reduced the material thickness between columns and rows – making the capacitive effect easier for the controller to read.

 
And a final thing I wanted was to fit the controller inside the keyboard. Xwhatsit is much too complicated for this and can only get so small. This was going to be my first use of DMA’s controller. Originally, I was going to put the controller directly on the pad card, but after some research, I changed my mind.

 
Over the next week or so, I’ll write an in-depth post on each … the case, pad card, and controller. Feel free to ask questions; I’ll try to answer in the write ups. I will be posting at Deskthority too (sorry reddit fans, I limit myself to two interest groups per subject and GH and DT were here first).
« Last Edit: Thu, 21 June 2018, 18:49:56 by wcass »

Offline BlindAssassin111

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Re: A Compact SSK Model F
« Reply #1 on: Thu, 21 June 2018, 18:53:52 »
This is pretty awesome, would like to hear how you did the controller as I have wanted to do something with capacitive switches and have no idea how it to do it.

Offline wcass

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Re: A Compact SSK Model F
« Reply #2 on: Thu, 21 June 2018, 20:11:01 »
I was planning on covering the controller in part 3, but ... no harm in discussing it a bit here.


DMA's CommonSense controller is tiny needing just 12 mm x 12 mm for components (excluding USB connector). I fit mine in the 12 mm gap between the nav clusters. I added some LEDs for Caps Lock and Scroll Lock. I also use a "one piece" board-to-board connector from Samtec. The connector (plus the controller PCB) are about the same thickness as the part of a barrel that is sandwiched between barrel frame and back plate. There is no solder connecting the controller to the pad card; the plates and barrels actually hold the controller in place. The only soldering involved in the entire keyboard is on this:



« Last Edit: Thu, 21 June 2018, 20:17:06 by wcass »

Offline BlindAssassin111

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Re: A Compact SSK Model F
« Reply #3 on: Thu, 21 June 2018, 20:38:51 »
I was planning on covering the controller in part 3, but ... no harm in discussing it a bit here.


DMA's CommonSense controller is tiny needing just 12 mm x 12 mm for components (excluding USB connector). I fit mine in the 12 mm gap between the nav clusters. I added some LEDs for Caps Lock and Scroll Lock. I also use a "one piece" board-to-board connector from Samtec. The connector (plus the controller PCB) are about the same thickness as the part of a barrel that is sandwiched between barrel frame and back plate. There is no solder connecting the controller to the pad card; the plates and barrels actually hold the controller in place. The only soldering involved in the entire keyboard is on this:
(Attachment Link)

That is pretty cool, Can't wait to see the whole writeup!

Offline 0100010

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Re: A Compact SSK Model F
« Reply #4 on: Thu, 21 June 2018, 21:42:50 »
Need more details!  Gives me hope for a B62 (beamspring 62).
  Quoting me causes a posting error that you need to ignore.

Offline wcass

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Re: A Compact SSK Model F
« Reply #5 on: Thu, 21 June 2018, 21:49:30 »
I would LOVE to do a beamspring. But i have now switches. If anyone has switches out there and wants them arranged a different way, let me know.

Offline Techno Trousers

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Re: A Compact SSK Model F
« Reply #6 on: Thu, 21 June 2018, 22:04:16 »
I have one... In the form of an Orihalcon keychain. :D

But yeah, I got excited about rumors of a modern version of the beamspring switch a while back, but maybe that didn't pan out.

Offline BlindAssassin111

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Re: A Compact SSK Model F
« Reply #7 on: Thu, 21 June 2018, 22:18:53 »
I have one... In the form of an Orihalcon keychain. :D

But yeah, I got excited about rumors of a modern version of the beamspring switch a while back, but maybe that didn't pan out.

Im debating about making them a thing...I just don't want to break my beamspring keychain, I like playing with it.

Offline wcass

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Re: A Compact SSK Model F
« Reply #8 on: Wed, 27 June 2018, 19:21:04 »
I call my keyboard layout the Compact Space Saving Keyboard or CSSK because it uses the same key cap set as the original SSK (plus a 1u caps between both Ctrl and Alt set) and does it in a package just 12” x 7” (300 mm x 175 mm). The caps are placed logically near where you expect them to be (except for Print Screen), and i think it combines the best features of 60% and tenkeyless. I have been using a chopped off M122 derivative of it for quit some time and am very happy with it.
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The first thing I did to make my keyboard was to prototype the case. I had a feeling this would be the most troublesome and expensive part of the project, so I wanted to make sure that it was right before I continued on with the rest of the process. Acrylic sheets come in standard thicknesses – multiples of 1.5 mm. I decided to use a 3 mm back plate, 4.5 mm spacer, 1.5 mm barrel frame, and 9 mm trim – for a total thickness of 18 mm. During the design process, I knew I needed to adjust the barrel for the caps to look right.

 
A Model F buckling spring barrel is 19.0 mm wide, but about 20.6 mm deep while the key cap is 18.6 mm wide and 19.3 mm deep. This is not a problem when the back plate has a curve, but when you flatten it out, the keycap rows get further apart. You can see this in the graphic below. My solution to this was to file off the front side of some of the barrels so that they were only 20.0 mm deep. This does not seem to alter the functionality.
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I sent my design off to built-to-spec.com for a RFQ in early September of 2017 … just before hurricane Irma hit south Florida. I didn’t have power and internet for a few weeks, so wasn’t able to give the go-ahead until December. I had delivery a few days later but the first test fit showed that alignment between trim and caps was off by 1.0 mm. I updated my design, ordered a replacement 1.5 mm barrel frame layer, and had everything assembled by New Years.

 
So, what did I learn? Acrylic’s glossiness is a fingerprint magnet, it flexes and cracks, but it is good and comparatively cheap for checking how things will fit together. I plan to make a final case using a single block of aluminum.

Offline Techno Trousers

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Re: A Compact SSK Model F
« Reply #9 on: Wed, 27 June 2018, 22:07:14 »


I plan to make a final case using a single block of aluminum.

I can't wait to see this! Is it going to be routed out of the aluminum block with the PCB sitting in the bottom?

Offline wcass

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Re: A Compact SSK Model F
« Reply #10 on: Thu, 28 June 2018, 14:45:13 »
I can't wait to see this! Is it going to be routed out of the aluminum block with the PCB sitting in the bottom?
That is the plan.

Offline Techno Trousers

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Re: A Compact SSK Model F
« Reply #11 on: Thu, 28 June 2018, 14:51:44 »
That'll be so cool!

Offline wcass

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Re: A Compact SSK Model F
« Reply #12 on: Tue, 31 July 2018, 18:03:40 »

The last couple of weeks, I have been working on the 3D model for the case and messaging with CNC vendors. I checked out eMachineShop, Xometry, and Fictiv. All were well outside my budget. The Chinese CNC shops were in budget, but communication, quality, and import tariffs could be a problem. Then i stumbled upon 100kgarages. I posted an early version of my design and a target price of $250 which was more than SuNPe quoted, but less than the US shops. I started getting quotes from maker members by the next day. A couple of the of the folks i chatted with pointed out some pain points. The original design had the space bar stabilizers fully integrated into the body. I knew that kind of undercut would be difficult, but thought it would be possible if i made a hole in the barrel frame below the overhang - so technically not an undercut. I was informed that chatter would likely rip the overhang right up.


I just placed an order for the aluminum case with Dalas at Rival Machining. This is what it should looks like.
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Since undercuts are so difficult to do, i built only the uprights for the space bar stabilizers into the body. The top of the stabilizer (1 mm thick flat) will be attached with an M3 screw. The 3 mm (1/8") thick base plate (not shown) will be attached with 20 Torx drive flat head M3 screws. Despite the lack of alignment pins, the barrels will be unable to move out of alignment because i have them completely surrounded by a tight fitting ledge (or another barrel). Another ledge (and 4 screws) keeps the pad card PCB from moving.
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« Last Edit: Tue, 31 July 2018, 18:07:00 by wcass »

Offline BlindAssassin111

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Re: A Compact SSK Model F
« Reply #13 on: Tue, 31 July 2018, 18:55:26 »
Wow that is going to be awesome!!! I wish I could afford to do a cool build like this.

Offline Meowsaur

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Re: A Compact SSK Model F
« Reply #14 on: Wed, 01 August 2018, 14:14:21 »
This thing is some heavy weaponry.
Looks bloody amazing.

Love reading about the process.
« Last Edit: Fri, 10 August 2018, 23:20:38 by Meowsaur »

Offline wcass

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Re: A Compact SSK Model F
« Reply #15 on: Wed, 08 August 2018, 21:19:19 »
Progress on the aluminum case.

The stabilizer tops were cut a couple of days ago on a brand new Tormach 1100.

Offline BlindAssassin111

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Re: A Compact SSK Model F
« Reply #16 on: Wed, 08 August 2018, 21:49:30 »
Progress on the aluminum case.

The stabilizer tops were cut a couple of days ago on a brand new Tormach 1100.

Wait so we get to see a video of it being machined later on?!?! That would be awesome to see.

Offline wcass

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Re: A Compact SSK Model F
« Reply #17 on: Sun, 19 August 2018, 21:45:23 »
The pad card is the PCB that makes up the switch matrix. Each switch has two parts; a signal pad and a sense pad. The pads are arranged with all of the signal pads on columns and all the sense pads on rows (or the other way around). The traditional design rules for the pad card is that all rows and columns cross exactly one time. Notice in the XTant pad card example below how the bottom row trace extends so that it can cross the two rightmost columns exactly once. Red color is the top layer, blue is the bottom.
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Also notice the wide right and top margins needed to route the columns and rows toward the controller. I wanted to see if I could make those top and side margins disappear. Compare that to the pad card of the CSSK. Red is again the top layer, blue is the second layer, green is the 4th layer. The 3rd layer is a ground flood (not shown).
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And now some CNC action ...

Offline wcass

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Re: A Compact SSK Model F
« Reply #18 on: Thu, 25 October 2018, 15:28:24 »

I finished programming the controller a little while ago. All done and it works great. Thanks DMA for the CommonSense. I think this proves that we can do pretty much any layout with capacitive buckling springs fairly inexpensively even at relatively low volumes. The 4-layer pad card was $100 for 5; the controller also $100 for 5. The expensive part is the CNC case, but it is definitely worth it. With that too - cost goes down as quantity goes up. You do need a supply of barrels, flippers, and caps. It would be great if we could find these easily.
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By the way, the LEDs themselves are white. I use a speedlite gel to change the color. A pack of 20 different color gels is $2 on eBay.
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Online LightningXI

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Re: A Compact SSK Model F
« Reply #19 on: Mon, 31 December 2018, 01:56:59 »
This project is incredibly cool -- has it finalized?

I would love to do something like this!
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Offline wcass

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Re: A Compact SSK Model F
« Reply #20 on: Mon, 31 December 2018, 10:21:34 »
This project is incredibly cool -- has it finalized?

I would love to do something like this!
Yes, it is done. I plan on publishing the design files ... soon. Similar CNC aluminum case designs will likely run about $600 - $1000 for one off, but price comes down as you make more. If you can find 9 people that want the same design, your cost per keyboard (case, pad card, controller) will likely be in the $300 (60%) - $500 (104 key) range.


There are not a lot of folks developing model F keyboards, keycaps, barrels, springs, and flippers. I would like to see more and hope that by publishing, promoting, and helping where i can - this might encourage other folks help where they can too. I am OK at innovation and PCB design, but uninterested (and unskilled) at finance and project management. I would be happy to advise and assist with other buckling spring projects, but you will never see me *run* a Group Buy.

Offline ramnes

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Re: A Compact SSK Model F
« Reply #21 on: Mon, 31 December 2018, 15:25:34 »
But how does it sound?!
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Offline iamtootallforthis

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Re: A Compact SSK Model F
« Reply #22 on: Mon, 31 December 2018, 15:27:25 »
But how does it sound?!

Awesome! I got to use it at the Florida East coast meet a few weeks back and it's real nice.

Offline wcass

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Re: A Compact SSK Model F
« Reply #23 on: Mon, 31 December 2018, 17:52:36 »
But how does it sound?!
I think it is louder than other Model F. There is no padding and the barrel holes are very tight, which i think lead to this. I will need to experiment more to see if this is so. It would be great if we could work out the formula so that we could tailor the sound level to a specific target. Also, I used a model F style space bar stabilizer; i think there is room for a model M stabilizer, but that too should be checked. And I would like to change the pad design on the pad card to take better advantage of the 4 layer PCB. Other than that, i think it is perfect.

Offline numist

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Re: A Compact SSK Model F
« Reply #24 on: Fri, 31 May 2019, 21:09:40 »
I'm toying with the idea of designing a capacitive ortho PCB for Model F mechanisms but am still familiarizing myself with the design constraints (am not an EE) so I have a couple questions!

All the pad cards (both IBM and hobbyist/clone) have a set of floating pads on the top layer over the connected pads on the layer below, which are shielded with a perimeter.

I assume the floating pads are to increase C when the flipper is down? How necessary is the perimeter?

Both of these features seemed like design compromises since the flex PCBs (as far as I can tell) didn't support vias, so one of the things I was considering for a flat board was having the row and column pads on the top layer together, with vias for the rows (or columns) to another layer for routing. Will I still need a shielding perimeter? Is there anything else I'm missing?

Offline wcass

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Re: A Compact SSK Model F
« Reply #25 on: Sat, 01 June 2019, 01:30:40 »
I don't have a scope or the knowledge to properly to answer this, but i have asked this question myself and got some help from a few friends. A while ago I had a bunch of alternate pad designs made and sent them to DMA. He did a write up on it (i think posted at DT), so i would suggest looking for that (please post a link if you find it). iirc, signal is stronger without the ground, but noise is higher too and likely not worth the trade off. Signal strength is much higher with both pads on the same layer. With a four layer board, top two layers are so close together that you get much of the advantages of "same layer", but are still able to route columns and rows with relatively few vias. I think i used about 12 or so for this.

Offline numist

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Re: A Compact SSK Model F
« Reply #26 on: Sat, 01 June 2019, 12:51:22 »
I think I found it: Alternative capsense patterns testing

It doesn't really get into the question of the floating pad and grounded perimeter but now that I've found the thread I guess I can echo my questions in there  :D

Edit: I also found this post which mentions vias offhandedly (6dB improvement!), but what's even more wild is that I found this image gallery of an original beamspring PCB and it appears to have both wired pads on the top layer and a complete ground plane behind them. I wonder how that affects things…
« Last Edit: Sat, 01 June 2019, 16:24:33 by numist »