| geekhack Projects > Making Stuff Together! |
| Let's replicate the Selectric keyboard mechanism |
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| enthdegree:
I own a mostly-functional Selectric II and after examining it for a while it seems within the realm of possibility to design and build a device that essentially replicates its typing feeling by re-implementing the keyboard mechanism. The keyboard portion of the Selectric mechanically converts a keypress into a bit string. Modulo friction and spring un-idealities, each piece of the mechanism fairly directly controls its part of the keypress force curve, a cartoon of which is shown here: http://bhtooefr.org/images/SelectricComposerForce.png An image on the following page is helpful for understanding the moving parts involved, although if I hadn't had real Selectric guts to look at it would have been hard for me to figure out what was going on. https://www.cryptomuseum.com/covert/bugs/selectric/#bin Essentially I am imagining deleting everything on the Selectric past the key-restore cam and replacing hard-to-source parts with easy ones (like helical springs instead of an ornate leaf spring). What is left over is a potentially extremely nice and interesting computer keyboard. Maybe with solid housing a solenoid could be added to emulate the feeling of the typeball firing. Has this been attempted before? You guys think this a stupid idea for a project? |
| yui:
from what i have read modified Selectrics where a pretty common keyboard for early computers. although it came with some majors drawbacks 1-1 key rollover, the keys get locked between key presses to make sure to only press one key at a time, and that is because of the encoding mechanism, so even if you remove the typing you will still get only 1 key rollover 2-Control keys, well those are missing 3-Mechanical to the extreme, it does make much more noise than even a model F, with that motor needed to make the whole thing work and much heavier weighting as well 4-There might be other reasons that i do not know/remember I guess IBM had a reason to develop the beam-spring switch, they wanted the Selectric without its shortcomings. Other than that you could do it, and you would not be the 1st doing so, linus tech tips even did a video on converting an old typewriter to usb |
| Findecanor:
--- Quote from: yui on Wed, 04 March 2020, 01:05:07 ---2-Control keys, well those are missing --- End quote --- Would it be possible to reuse the Lock key for that purpose? --- Quote from: enthdegree on Wed, 04 March 2020, 00:38:33 ---(like helical springs instead of an ornate leaf spring). --- End quote --- Just don't replace any spring that is part of the key feel! |
| enthdegree:
--- Quote from: yui on Wed, 04 March 2020, 01:05:07 ---from what i have read modified Selectrics where a pretty common keyboard for early computers. although it came with some majors drawbacks 1-1 key rollover, the keys get locked between key presses to make sure to only press one key at a time, and that is because of the encoding mechanism, so even if you remove the typing you will still get only 1 key rollover --- End quote --- I was thinking about this a bit today and the locking mechanism shouldn't pose a problem for NKRO. A keydown on a selectric sets an interposer into an active position and then pushes a cycle bail. When the cycle bail is pushed far enough that a latch gets past some ledge, the selectric fires the typeball with the interposer in place, while returning the interposer to its initial position. This is all without a keyup happening. While you are still holding that key is down you can go press other keys and the same described process will happen. The only thing the locking mechanism prevents is attempting to push keys down exactly simultaneously. One difficulty I can think of is the need to develop an additional mechanism that broadcasts keyups. I am thinking keyup signal needs to be created using the keylever itself somehow, since that's essentially the only moving part. I hope an elegant solution to this can be developed. --- Quote from: yui on Wed, 04 March 2020, 01:05:07 ---2-Control keys, well those are missing --- End quote --- That's fine, I can give meta keys their own set of selector bails. --- Quote from: yui on Wed, 04 March 2020, 01:05:07 ---3-Mechanical to the extreme, it does make much more noise than even a model F, with that motor needed to make the whole thing work and much heavier weighting as well --- End quote --- This is a feature, not a bug. --- Quote from: yui on Wed, 04 March 2020, 01:05:07 ---4-There might be other reasons that i do not know/remember I guess IBM had a reason to develop the beam-spring switch, they wanted the Selectric without its shortcomings. Other than that you could do it, and you would not be the 1st doing so, linus tech tips even did a video on converting an old typewriter to usb --- End quote --- I don't think IBM and the guy you mention, Linus, had the same goals in mind... |
| enthdegree:
I've been overcomplicating things... All the selector bails and interposer patterns are totally unnecessary. Keypress-to-digital signal conversion can be done just by a sensing mechanism on the microcontroller, say, a capsense or magnetometer array right underneath the keylevers. This automatically gets you NKRO and everything. |
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