Handheld Chord Key Switch

[whoisterencelee]

Recently saw this tabstrummer on hackaday.com and I asked the designer what the exact switch are being used, but designer refused to give answer, so wondering if any expert here can tell me the answer.  



What I am looking for actually are switches to use for a project of mine which is a device that is handheld and allow chord (multiple pressed key) input, which is similar to what you would do on a guitar, any recommendations?

Am I correct in thinking that for chord input, mechanical switches would be better because:
- less strain because a key would already register before hitting bottom and so less force is required?
- the spring would return the key to off/up position faster, so the user feels the key is in constant contact?

Terence

[whoisterencelee]

Further to my original post, I've search thur the forum for chord input switches but seems there's not really any recommendations for mechanic switch for chord input device...

I looked deeper into the web and found a Marquardt Series 6425 switch at http://www.marquardt-switches.com

This switched was found from a part list of a project called spiffchorder and seems to be used by several chord input projects.

Not sure if anyone here used this for a chord project, and what's their experience is with this?

Since I am new to this, what do I need to consider when choosing a chord input switch?

[edada]

Hi Terence, I think I'm newer than you to this but I have a few knowledge that may help you.

About the "multiple pressed keys" issue, switches are not implied. You'll learn why most keyboard fail on this here : http://www.microsoft.com/appliedsciences/AntiGhostingExplained.mspx
To correctly detect lots of pressed keys you just need a lot of diodes. You will find complete informations by searching "NKRO" here.

On most instruments, we have to "bottom the keys" to get the sound. On most mechanical keyboard switches, the actuation point is over the bottom, thus if you bottom a key and then release it about a milimeter it will stay on, while on a musical instrument this action may kill the sound.

About strain, did you ever play double bass ? Even compared to the lighter guitar strings, any switches will feel light. I believe you should not take care about force if the thumb is placed in opposition.

[whoisterencelee]

Thanks.  Ah yes, I am aware of the ghosting problem with matrix based keyboard, it is easy to resolve when you only need to press and hold a few keys like asdf.

I am pondering about the "bottom the key" issue for handheld chording, for musical  instruments I see how the click noise can be a problem, and maybe the tabstrummer is some how able to solve it.

For my project the click is not the biggest concern unless it creates strain from the vibration.  The problem with any chording device is that compare to a 1 to 1 character input mapping like a keyboard, not only does one need to press more keys to get one character 3 to 1 char mapping, but I believe chord user will tend to press harder since the intention is to press and hold.  In this case, is "bottom the key" a good or bad thing for chording?

You have brought up a good analogy of playing the guitar, I have handled a guitar before and my experience is that I tend to press really hard on the string, is this normal?  Or do professional musician press more lightly?  If not this is again the reason I am looking for switches which is comfortable for chording.

Also I see how the thumb if placed in opposition and help reduce the force required for chording, in general I think if the hand is in a open position with thumb opposition is the best and better yet if the fingers do not need to reach out like playing the guitar.

[edada]

Clicks are not a big problem for an electronic instrument, as they may not be heard by auditors, for sure you'll get more pleasure playing without parasitic sounds. Never heard about something like strain caused by click vibration.

Problem with bottoming while touch-typing is the huge number of impacts, you won't play chords as fast as you type. Also it seems obvious for me to bottom a key if I want to hold it. Should be less injurious than holding a pen. I believe you will get the best feeling with switches that register at bottom.

Also I believe professional guitarists press harder than beginners, because it sounds better, and they have thicker skin on fingertips that help them painlessly pressing hard.

Placing the thumb in opposition don't actually reduce required force, but helps to get only the fingers working and increasing pressure on strings. If you release the thumb all the arm has to press, and it will mostly strain your wrist.

[flyball]

Am I correct in thinking that for chord input, mechanical switches would be better because:
- less strain because a key would already register before hitting bottom and so less force is required?
- the spring would return the key to off/up position faster, so the user feels the key is in constant contact?

sure but you would probably prefer microswitches. think arcade pushbuttons

[whoisterencelee]

Think I misunderstood you the first time about "bottom the keys" for music instruments, you meant this is bad for musical instruments because the "on" duration could be longer than expected due to the button still active 1mm above bottom.

I think for chord input (non-instrument) this is both good and bad, the good thing is that when multiple keys are being pressed one of the fingers that is suppose to press down might lift just a little but the chord would still register; on the other hand you have the above problem when you release the key.  This is getting complicated...

So I want to bring the musical instrument analogy again but with trumpet, which I think are probably closest to what I am looking for.  I've played the trumpet before, and the keys are always responsive and they basically maintain contact with my fingers, and there's no need to extend the fingers for trumpet (there are only three keys if I remember correctly).  Are there any mechanic switches like this?

Placing the thumb in opposition don't actually reduce required force, but helps to get only the fingers working and increasing pressure on strings. If you release the thumb all the arm has to press, and it will mostly strain your wrist.

Yikes, that does sound painful.  Actually I give up on guitar before due to the pain on finger tip... :^)

[whoisterencelee]

Arcade buttons I think are good for fast action, and edada might agree with me, but I believe we can't chord as fast as typing, and definitely not as fast as arcade.

However, I do see a few chord projects online that uses microswitch, I think they mainly chose to use that for the lower cost.  I have handled microswitch before and their arms tend to bend after excessive use and their contact area are quite small, what do you think?

[edada]

You must hack a trumpet with some kind of switches ! )

Arcade buttons are also good for slow action, I talked about speed to mention that you may not get RSI by playing with your chord device, challenge is really different that with a text input device.

Microswitches are also available without lever, this is what's in most arcade buttons, but you should have a button beetween switch and finger. About price, you may find an old computer keyboard with a hundred switches for the price of a pair of brand new microswitches.

Think I misunderstood you the first time about "bottom the keys" for music instruments, you meant this is bad for musical instruments because the "on" duration could be longer than expected due to the button still active 1mm above bottom.

I think for chord input (non-instrument) this is both good and bad, the good thing is that when multiple keys are being pressed one of the fingers that is suppose to press down might lift just a little but the chord would still register; on the other hand you have the above problem when you release the key.  This is getting complicated...

There will be no unsolvable duration problem, as you will adapt yourself to the switches, but you may have a problem with feeling. For the loosening fingers, it could be solved with electronics or software, by keeping the chord registered until all fingers are up.

…for chord input (non-instrument)…

Huho ? I'm just realizing your project device is maybe not a musical instrument, isn't it ?

[whoisterencelee]

Oh, the project is a non-musical devices, it's for text input.

I guess there are micro switches without the lever liked that you could find in a mouse button and I think these are similar to the arcade button switches, but I think the travel distance offered by these switches are too short.  If this devices is to be adapted by mainstream, it has to feel intuitive and I think I've so far figured out some of this.

I've searched for "electronic trumpet" and found one, and they built their own custom trumpet keys and use optical sensors.  Overkill for a prototype, maybe not for volume.

I think in the end, the correct feel would be similar to playing a trumpet.

[edada]

I've said some pointless things then … You misleaded me with the TabStrummer and guitar similarities, I now know you are planning to build what Wikipedia calls a chorded keyboard. But I'm happy it leads to some interesting ideas.

Small IR barriers are cheap, you'll find some in old mouses (non-animal — the pointing device). You must find a dead trumpet with working pistons and hack it !

As I was trying to figure out how you would play lot of loud chords with few switches, I'm now planning to turn my keyboard into an accordion. Definitely need NKRO.

[whoisterencelee]

Actually, some of the things you said was useful, and I think it finally lead me to the trumpet idea.

I think to build a prototype I will use the switches I mentioned in the 2nd post, as it's being used by other chorded keyboard projects.  But I will keep the Trumpet idea in mind, because I still think a successful chording device must have better "feel" than keyboard.

Yeah, NKRO is easy to resolve if you only limit yourself to a few keys, I actually figured this out by taking a keyboard apart and checking to avoid keys which are on the same circuit line.

I have thought about a web app which allow people to play music on their keyboard, NKRO would be something to keep in mind.