A Guide For Building Rubber Dome Keyboards

Let’s talk about computer keyboards for a second. The worst keyboards in the world are the cheap ‘rubber dome’ keyboards shipped with every Dell, HP, and whatever OEM your company has a purchasing agreement with. These ‘rubber dome’ keyboards use a resistive touchpad to activate a circuit, and the springiness of the key comes from a flexible rubber membrane. Mechanical keyboards are far superior to these rubber dome switches, using real leaf springs and bits of metal for the click clack happiness that is the sole respite of a soul-crushing existence. MX blues get bonus points for annoying your coworkers.

Mechanical key switches like the Cherry MX, Gateron, or whatever Razer is using aren’t the be-all, end-all mechanical keyswitch. History repeats, horseshoe theory exists, and for the best mechanical keyswitch you need to go back to rubber domes. Torpre switches are surprisingly similar to the crappy keyboards shipped out by OEMs, but these switches have actual springs, turning your key presses into letters through a capacitive touchpad. Is this a superior switch? Well, a keyboard with Torpre switches costs more than a keyboard with Cherry MX switches, so yeah, it’s a better switch.

It seems everyone is building their own mechanical keyboards these days, and the recipe is always the same: get a few dozen Cherry MX (or clone) switches, build a PCB, grab a Teensy 2, and use the tmk keyboard firmware. There’s not much to it. DIY Torpre boards are rare because of the considerations of building a capacitive switching PCB, but now there’s a DIY guide to making the perfect rubber dome keyboard.

[tomsmalley] put together this guide after reviewing a few amazing projects scattered around the web. Over on Deskthority, [attheicearcade] is building a custom, sculpted, split Torpre board and a split Happy Hacking Keyboard. These are projects worthy of a typing god, but so far there has been no real beginner’s guide for interfacing with these weird capacitive switches.

As far as circuitry goes on these capacitive boards, the PCB is the thing. Each key has a pair of semi-circular pads on the PCB to serve as plates on a capacitor. These pads are connected to a microcontroller through an analog mux, with a little opamp magic thrown into the mix.

With a relatively decent guide to the hardware, [tomsmalley] has also been working on his own firmware for capacitive switches. Shockingly, this firmware is compatible with the Teensy 3.0, which will provide enough horsepower to read a bunch of analog values and spit out USB.

Mechanical keyboards are great, and we really like to see all these hardware creators pushing the state of the art. You can only see so many custom sculpted keycaps or DIY MX boards, though, and we’re really eager to see where the efforts to create a custom Torpre board take us. If you’re building one of these fantastic keyboards, send it in on the tip line.

43 thoughts on “A Guide For Building Rubber Dome Keyboards

  1. “Well, a keyboard with Torpre switches costs more than a keyboard with Cherry MX switches, so yeah, it’s a better switch”

    Sorry, but you lose me with the thesis that more expensive switches (or anything, for that matter) are necessarily better.

        1. I’d just like to interject for a moment. What you’re referring to as autism, is in fact, autistic humour, or as I’ve recently taken to calling it, autism plus humour. Humour is not an outlook unto itself, but rather another free sense of a fully functioning autistic personality made useful by the autistic attention to detail, obsessive ramblings and vital system senses comprising a full personality as defined by DSM IV. Many brain users run a modified version of the humour personality every day, without realizing it. Through a peculiar turn of events, the version of humour which is widely used today is often called “Autism”, and many of its users are not aware that it is basically the humour personality, developed by the humour Project. There really is a certified autism, and these people have it, but it is just a part of the personality they use. Autism is the modus operandi: the thought in the personality that allocates the brains’s resources to the other thoughts that you think. The modus operandi is an essential part of an outlook, but useless by itself; it can only function in the context of a complete outlook. Autism is normally used in combination with the humour outlook: the whole personality is basically humour with autism added, or humour/autism. All the so-called “autism” jokes are really jokes of humour/autism.

          1. Do wish you had continued further… Such explanatory clarity on this subject is rare, and I had to raise him alone. The so-called experts were NOT. They simply bullied and spouted judgemental attitude, and scattered away like mice when asked to put it in writing or provide assistance of actual value, but they did bill liberally! Quite reasonable success was still managed, thankfully it was not profound, yet definitely took the effort. But now I’m dealing with a step-grandchild and his is very profound.

            Thank you.

    1. yea i found a cherry based mechanical keyboard in a dumpster awhile back. ive been meaning to clean it up and 3d print some replacement keycaps (a few were missing which is why they threw it away, all the switches seem to work though). still it sits attached to an old computer i boot only when i need to use my 3d printer and still hasn’t made its way to my main gaming/programming rig yet. i like the sound and the size of the key drop, but thats about it. im still using my crappy dell keyboard (also found in a dumpster) because i like the more or less standard layout and the media buttons and volume knob (and my true loyalty will always lay with devices with knobs). as for people who pay money for keyboards rather than refurbish ones found in dumpsters, lol.

    1. ive used one of those before. they are ok, but you need a huge desk to hold it off the ground. you can also use it to fight off burglars who are trying to steal your keyboards.

      1. I’ve seen it stand up to a MMA fighter/instructor punching the keyboard – knuckles first – without any lasting damage except for bleeding knuckles. The table did survive, suprisingly …

  2. There’s nothing wrong with the rubber domes. They’re just tunable progressive springs, which is very hard and expensive to accomplish with metal springs. The actual problem of rubber dome keyboards is anything but the dome or the underlying switch itself – it’s usually the pressure molded key guides and keys with sloppy tolerances that rattle and wiggle and stick and feel “mushy” because they won’t align properly with the domes.

    A superior keyboard has three properties 1) short straight travel, 2) soft bottoming, 3) tactile but quiet operation. The stress on your tendons and joints is caused by force over distance and high accelerations, so minimizing movement and forces/accelerations minimizes RSI, and you simply don’t need the clacky noise to type – the sensation through your fingers travels faster than the sound through the air. The “tactile” nature of clicky keyboards is just magical thinking – it’s doing something so it’s “better”. Same thing as with vacuum cleaners – the noisier it is the better it sucks – at least that’s how people feel.

    A scissor switch key is actually the best: it has a distinct tactile point, very short travel, and the operating or switching point is very soon after the tactile point, so when the dome starts to buckle the switching is more or less assured. As soon as you feel it go, the switching happens. Other switches, ‘mechanical’ switches like the Cherry MX ‘brown’ have the tactile bump and the operating point well separated and you have to press them all the way in to ensure switching, which causes people to learn a hammering style of typing instead of trusting the keyboard to do it’s job. It’s slower, louder, and causes more strain on your hands, but again it feels like you’re really doing something so it must be better.

      1. Bascally, the peak force is when you feel “now it switches”, and the activation or operating point is when it actually switches. Hence why on switches where the two are separated by a great deal of travel, you have to “hammer” the keys to make sure it switches. Otherwise you may end up lifting your finger too soon after feeling the tactile point and you get a typo. On keys where the two are a shorter distance apart, you can trust the keyboard and type lighter and faster.

        1. Plus, as we know: work (energy) equals force over distance. The work required to reach the switching point can be measured as the area that falls under the graph. The scissor switch gets the smallest area up to the switching point – ergo it stresses your hands the least to type on – despite the relatively high force required to press the key.

          Typing on the other key switches causes you to spend more energy, some of which is lost to the mechanical inefficiency of your tendons and joints, and that ends up causing the damage that leads to RSI.

        2. I thought I was the only one that preferred laptop keyboards. I’m definitely a fan of lower travel and lower force required to activate scissor switches. I don’t like how far you have to press a mechanical key to get it to actuate. If people are used to typing on either cheap membrane keyboards or mechanical keyboards, I can see why they do not like scissor switch keys as they are most likely using the techniques they use on those other styles which don’t work as well on scissor switches.
          However, I would like to give this keyboard a try:

          1. I’ll get all sorts of hate for this here in sure, but you can pry my Apple wireless keyboard out of my child dead hands.

            I can’t stand the cherry/model m type keyboards.

      2. That’s _one_ scissor switch, not all scissor switches. The ones I’m typing on right now have a very high tactile event, and actuation is at the bottom like all membrane rubber domes. I’d like to know more about how those graphs were made—the legend calls the black dot “actuation force”, which sounds to me like it might be from some advertised figure rather than a real measured actuation _displacement_.

        1. That’s true – there are different domes under the different scissor switches from different manufacturers. However, the overall space constraints make them more or less similiar in action: the switch has to close fairly early on because the user can’t keep mashing the key against the “hard wall” at the back of the travel. There have been such keyboards and they all feel perfectly awful.

          1. Please explain to me how a stabilized rubber dome over membrane switch could actuate before the dome bottoms out, preferably with links to third parties to verify your claims. I have no idea how that could work, and asserting that it does fails to sway me.

          2. There’s not a lot of information on scissor switch keyboards to be found on google, or at least I can’t find any.

            But the issue is easily verified empirically. Set up a steady lever or a screw over a laptop keyboard and depress the button gradually and observe when the letters start appearing on-screen. Is it at the bottom or not?

          3. Here’s an extremely simple test setup to verify the claim. A slender piece of wood pivoted over an axle sitting in a notch cut in said lever, with a screw at the back end thrusting against the base of the device, the other end of the lever is resting on the keyboard to be tested. Pressure is applied by finger on the pivot point and the screw adjusted until simply touching the far end of the lever over the key causes the key to trigger. Then further pressure is applied to feel whether the key moves freely or not.

            With my particular keyboard I observed that beyond the point of key triggering, there was a distinct amount of free travel until the key feels to bottom out, which indicates that the trigger event is happening if not on the peak force point, then at least on the downslope soon after the rubber dome has buckled.

            A more elaborate version of the test setup would have a stiff leaf spring extending over the end of the lever, the tip of said spring would press against the key, and an optical gate would be used to measure the deflection of the spring to indicate force. A simple voltmeter is sufficient to detect relative magnitude of the force. By that setup you could observe how much relative force is required to buckle the key and how much to trigger it, finding out how soon after the tactile point the switching actually happens.

          4. >”how a stabilized rubber dome over membrane switch could actuate before the dome bottoms out”

            Assuming capacitive sensing, you can dial it to any arbitrary point you want. Otherwise, you add a flexible bump underneath the dome that touches the membrane before the walls of the dome have fully collapsed.

            In the interest of science I did a better test setup and found out that indeed, there’s about 0.8 mm travel between where the dome buckles and when the key triggers on my keyboard. It is indeed actually closer to the back wall than to the buckling point. That said, it feels virtually impossible to press the key without triggering it because no matter how lightly you try it’s just too short of a distance to stop yourself. Only if you dial the screw just past the buckling point it becomes possible to lightly press it without triggering the action.

            (it’s a link, not a broken image)

    1. Pretty sure this is what the apple aluminum keyboards (wired with the numpad) use and is why I love them. I’ve never understood the appeal of having to have so much travel between pushing the key and the activation. Then again 90% of my keyboard use is one handed for shortcut keys and not typing. Which is also why I like the almost completely flat keycaps on the apples. Super easy to glide your hand across to the key you need.

      if they ever stop making them I’ll probably have to stock up. Though I have a couple that have seen daily use for 5+ years and are going strong still.

      Also easy to clean and relatively cheap (compared to 100$+ ones with fancy keys.)

      1. I think those keyboards are actually standard dome switches instead of scissor switch.

        And I think those “island”/”chicklet” keyboards are an abomination, because I prefer compact keyboards to minimize finger travel. The issue with compacts is the often nonstandard key arrangement and lack of pg-up/down and other special keys.

        1. I fail to see how a (example only) 15x15mm chicklet key changes the distance of travel compared to (still example) 17x17mm standard/domed/whatever key. The distance between key centers are approximately the same between keyboards after all, the difference is what the dead space between keys is (not) used for.

          1. If the key is 15×15 mm instead of 17x17mm then why didn’t they fit them closer together? Why is the keyboard unnecessarily large? That’s the point.

            It’s a design choice to have large keys. It’s not necessarily a good choice since an offset keypress leads to the key binding/sticking in its socket more easily. A compact keyboard in my opinion is better because it allows for lesser finger travel, so it’s just dumb to install smaller keys and then leave huge gaps in between.

            And those chicklet keyboards are often not scissor switches but the standard and cheap cylinder in a tube keycaps over rubber domes. Those suck because of the wide tolerances between the key cylinder and the socket as they come out of the injection mold with varying levels of shrinkage.

  3. A well made keyboard can last decades in daily use so it is worth making one that is perfect for you if you have the ability to do so. Make sure you mill the key symbols into the keys though or you will find them wearing off eventually.

  4. There is a keyboard for organ that has a break in the keyfall force, the force when held down is less than going down by a significant amount. They use a larger rubber dome. Of course one does not normalllllllllllllllly hold down typing keys like in music. They also have to be silent. All this is done to mimic the valve opening on a tracker pipe organ where there is a mechanical linkage from each key to each chest of valves and pipes. The key talks back to the finger.

    Greece-Roman engineering.

    This is the inspiration for all that followed.

  5. > The worst keyboards in the world are the cheap ‘rubber dome’ keyboards shipped with every.

    False.. Try the silicon-cap keyboards used on 90’s cellphones, certain Sinclair computers and those stupid $10 ‘waterproof’ eBay specials. These ship with everything because they work, well enough to pass stringent ergonomics tests that means they don’t injure *most* users when properly placed.

    > Mechanical key switches like the Cherry MX, Gateron, or whatever Razer is using aren’t the be-all, end-all mechanical keyswitch.


    > for the best mechanical keyswitch you need to go back to rubber domes.

    Probably false. The IBM/Unidata ‘buckling spring’ is still to my knowledge widely considered the optimum mechanical key mechanism?

    > Well, a keyboard with Torpre switches costs more than a keyboard with Cherry MX switches, so yeah, it’s a better switch.

    I don’t know about ‘autist humor’. This just looks like misinformation to me.

    > DIY Torpre boards are rare because of the considerations of building a capacitive switching PCB

    I would have guessed that hackers prioritize. 1. Fun. 2.Cheap. 3. Cool. 4. Elegant. 5. Practical solution. While elegant, this solution doesn’t really have anything over Cherry MX in the other categories.

    > [tomsmalley] put together this guide after… Over on Deskthority, [attheicearcade] is building… These are projects worthy of a typing god…

    Interesting, thanks!

    > As far as circuitry goes on these capacitive boards, the PCB is the thing. Each key has a pair of semi-circular pads on the PCB to serve as plates on a capacitor. These pads are connected to a microcontroller through an analog mux, with a little opamp magic thrown into the mix.

    Good summary.

    >Shockingly, this firmware is compatible with the Teensy 3.0

    Danger! High voltage!

    > only see so many custom sculpted keycaps or DIY MX boards, though, and we’re really eager to see

    Yeah, great hack. I prefer laptop-style keyboards, but still a cool bit of DIY engineering.

  6. I’m in the market for a new keyboard, I’m currently using a Razer Arcosta, really nothing special but it works okay.

    The give and the actuation is impossible to differentiate. But they still have that horrible bodgy feeling.

  7. I know there is a mechanical keyboard craze, but do we really have to pretend dome is ‘the worst ever’? In fact bad dome is mostly about the guiding system of the key movement rather than the dome system. But that’s not THAT common.

    Not that I ever bought a pre-made system, but I do use cheap keyboards though.

    Oh and on the ‘new’ front, they now introduced a key (and keyboard) that uses an IR interrupt sensor instead of contacts that is suppose to be long lasting and quicker since it does not require debounce.

  8. I’m showing my age here because I learned to type on a manual typewriter…yes, one that had full travel and the actual keys struck the paper and went clickity clackity as I typed 40-60 words per minute onto paper and the ink was permanently set onto the paper. Then came white out and then the IBM Selectric typewriter with the rotating ball and electrical switches in the keyboard. We interfaced those types of electric typewriters into the early CP/M computers as input devices. From then on, the keyboard has become a necessity and therefore a bone of contention about what type is best. I’ve used just about every type ever developed and even worked on the invention and development of electronic capacitive keyboards and membrane keyboards very early on. Let it be said that the value of a keyboard is what the person using it perceives. Right now I’m using a rubber dome keyboard on an obsolete, in some people’s opinion, HP Presario X1000 laptop. I find that even more modern laptops have decent keyboards but then again, I am not a gamer, just a text typist. I sold early ASCII keyboards made by Clare Pendar and even AIM-65s that had matrixed keyswitches on their keyboards. If the keyboard functions properly for the market it is sold into and lasts beyond the intended market life of the product, it has performed well.

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