Force curve of Selectric keyboard?

[bhtooefr]

Has anyone found a force graph of the Selectric? It'd be interesting to compare to other keyboards.

[kill will]

I have a selectric 3. And it is my goal to make it a USB keyboard one day.  The key feel is very unique and gratifying.

[kill will]

I would say the f orce curve is linear, low force with a bottoming out mushy feel.

[bhtooefr]

Which link, I'm not seeing it in the Selectric link?

Also, perspective makes it hard to tell, but is that about 4.5 or 5 mm?

[ch_123]

Ripster, would it be fair to say that the Selectric is linear for a bit, then snaps?

[ch_123]

So, Selectrics actually have a leaf/beam spring in them? Interesting.

What I mean in terms of linearity is whether or not it builds up in a linear fashion, or whether it's a bit bumpy like a Cherry or whatever. I had read a description somewhere that the Selectric was linear up to a point, then snapped in nicely.

[ch_123]

Well, leaf spring and beam spring are two names for the same thing, the last I checked.

[bhtooefr]

Like a Cherry blue would be an acceptable, but very inadequate description.

The bump is far larger and smoother than that, and you don't feel it on the return stroke.

[ch_123]

I just looked at your article. So they are like are sort of free-hanging springs as opposed to being tensed between two points.

This snapping thing adds credence to the idea that the Beam Spring was designed to emulate the Selectric. The beam spring snaps in a way that no other keyboard switch does.

[bhtooefr]

I find that the beam spring has a somewhat different force curve to the Selectric.

The Selectric has quite a lot of travel (2 mm or so?) where there's almost no resistance, before it hits the "big bump".

The beam spring starts out in what would be the Selectric's big bump, but rather builds in pressure when approaching its tactile point.

Tactile points are in similar locations relative to bottoming out, but the beam spring's tactile point is rather weak, IMO. You don't get the sensation of your finger being pulled down like the Selectric gives you, or like even buckling spring can give you, at least based on my board.

[bhtooefr]

No, I haven't.

Link to that build?

[ch_123]

If someone made an adapter for a Beam Spring board, I'm pretty sure I would have heard about it by now

[Soarer]

Hmm, maybe, but which beam spring keyboard was it? They all seem to have slightly different interfaces on them. I'm in the process of working out an adapter for the DisplayWriter board, which appears to have at least some similarities to the 3104 board (see kbdbabel for that one), but is simpler.

[Soarer]

Ah, thanks.

Having the base unit would make deciphering it easier, since you can just look at the signals with a scope! There doesn't appear to be any info on the 3727 on kbdbabel.

I know nothing about that model, but I bet it has an interface that slightly different to anything else :-/

The most general solution would be to mostly gut the controller board, and drive the capacitive sensing chip from a Teensy (or whatever). Then we would have a way to get any of them working, since mostly they use the same chip (I think, or there may be two variants). That would also allow for sending the release code at the right time (otherwise, an adapter may only see a make code for non-meta keys, and has to send a release code straight away).

But that is destructive :-(

[Soarer]

Well I've no doubt that replacing the controller chip would work!

Second problem is that the layout on many of these boards is a bit whack for modern use - DisplayWriter seems to be one of the most sane. And without sending release codes, you can't move the modifiers around at all, or add any extras (e.g. for Fn, to access a second layer).

[Soarer]

That fits on there just fine!

[bhtooefr]

Hmm, that would be an interesting as hell approach. Get a real 5251 terminal, an AS/400 portable, and write an OS/400 app to connect to a computer over VNC to send keystrokes?

In any case, the 5251 (and, IIRC, one other) layout is the closest of all beam spring layouts to a layout used on the PC. (The original Datamaster and PC Model Fs, in fact, used the same layout. )

[ch_123]

Hmm, that would be an interesting as hell approach. Get a real 5251 terminal, an AS/400 portable, and write an OS/400 app to connect to a computer over VNC to send keystrokes?

In any case, the 5251 (and, IIRC, one other) layout is the closest of all beam spring layouts to a layout used on the PC. (The original Datamaster and PC Model Fs, in fact, used the same layout. )

I'd argue that the Displaywriter had a far more usable layout. It's sort of like the AT, with rows of keys on the right instead of a numpad. I'd be somewhat willing to argue that the latter is more desirable.

[Soarer]

Hmm, that would be an interesting as hell approach. Get a real 5251 terminal, an AS/400 portable, and write an OS/400 app to connect to a computer over VNC to send keystrokes?

In any case, the 5251 (and, IIRC, one other) layout is the closest of all beam spring layouts to a layout used on the PC. (The original Datamaster and PC Model Fs, in fact, used the same layout. )

Oh, one of these? As ch_123 says, that's a matter of taste. I quite like a 2x4 block for nav keys, but numpad is ok by me also.



I see why you suggest the portable option, although this is still quite a tidy unit...



Delightfully over the top for connecting a keyboard to a PC!