deskthority

Okay, it's more like a harpsichord than a piano, if some of you may know what I mean.

To sense the exerted force in a keystroke is not possible in any of the switch in the market, and I am not aware of any (computer keyboard switch) design out there that is implementing this feature. I wonder what is the engineering mechanism for sensing variable force in some of the electronic piano keyboards. The force curve for such a switch will be like a linear at the beginning but an exponential function towards the end of the key stroke.

Menuhin wrote: I wonder what is the engineering mechanism for sensing variable force in some of the electronic piano keyboards. The force curve for such a switch will be like a linear at the beginning but an exponential function towards the end of the key stroke.

Spoiler:

Some electronic keyboards actually have 2 switches under each key and they calculate how fast you press each key.
Other Electronic musical keyboards (the more expensive ones) have Hall effect switches.

But the awesomest switches I have seen on a "musical keyboard" are those on the Seaboard:
I am extremely curios to learn what kind of sensing mechanism it has

Menuhin wrote: To sense the exerted force in a keystroke is not possible in any of the switch in the market, and I am not aware of any (computer keyboard switch) design out there that is implementing this feature.

This is true only in the strictest sense, but not true for the purpose you are thinking about:

A) several traditional mechanical computer keyboard switches (or many mechanical switches) show a bounce waveform that is strongly dependent on the speed the key was pressed with - which, with the proper controller and sensing arrangement, can be sensed and the speed deducted. This obviously won't be as precise as a purpose-built musical keyboard, but at least some rudimentary speed sensing should be possible. (This is one item on my plate of experiments I want to work on.)

B) position sensing can be used to sense speed, which can be used to sense force/intent/musical "velocity" (in the MIDI sense). for this, you can use position data from switches that support it; these could be linear capacitive switches (notably foam and foil or I guess also topre), linear/proportional hall switches, or those optical switches that someone brought out last year which is basically a reflective optocoupler with the switch stem being the reflective surface, in essence continuously measuring the position of the stem.

The video is surprising to me: it would imply that the DELL laptop scissor-switch membrane keyboard is NKRO. I can't imagine how the chords could be properly scanned -- ghosting and "sneak-routes" (in VT100 parlance) would defeat accurate detection if more than two keys are pressed.

Not necessarily. 2KRO means that there is at least one key combination of three keys that would not be possible without ghosting. It does not preclude that there are possible key combination with more keys at once.

derzemel wrote: Some electronic keyboards actually have 2 switches under each key and they calculate how fast you press each key.

I think that is the norm. Let me continue to illustrate further:
A clavier key is a lever so when you press it, different parts of the key will reach different depths at a given angle. A switch at the front of the key will therefore reach actuation distance before a switch further up will. The construction is therefore very simple: all switches can be one a single PCB or membrane.
An actual piano requires that you press a key with a certain speed to make a sound - if you press a key too slowly, it will be quiet.

There are some vintage keyboard switches that actuate different key signals at different key depths.
Topre's capacitative sensing is also able to read travel, and therefore speed. They have shown a prototype QWERTY keyboard that could be put in MIDI mode and played with speed sensing.

BTW, on older musical programs for computers there has been a convention where the QWERTY keys are white keys in one octave with the numeric row black keys. Then the ZXCV keys are white keys in another octave with ASDGF being its black keys.

To calculate the strength of a key stroke on a electrical or electronic keyboard instrument,usually instead of directly measure the strength of the stroke,they calculate the velocity which can reflect how strong a key is pressed. There are two switches aligned in line under each key, when you press down a key, always one switch is registered first and another later(due to the angle of the key pressed), to calculate the time between the two registration, the instrument knows how hard you've pressed the key.