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Topic: one-string piano (Read 2759 times) previous topic - next topic



i just wanted to ask you guys about the feasability of this project, and whether you think i would actually need an Arduino to do this, or i could also (maybe better?) do it with 'general electronics'.

imagine a player piano, so a piano that plays by itself. what i want is to make that, but with one string only, and the mallet that plays the string can be moved up and down the string. this idea was born from string the high E string on a guitar with a metal object, moving up and down the string, thus changing the pitch.
i want the mallet to strike by itself, in a rhythmic way. the speed of the rhythm should be changeable. for now, i figured i could have a steady rhythm, but typing this it might also be good to have multiple options here (new ideas come in as we speak).

what i have thought of so far is to use a servo to control the mallet's rhythmic thumping, and simply have that on a movable construction hooked to a big slider.

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|_ _ _ _ _ _ _ _ _|

something like that, the - - - being the one string inside the box, the [] is the mallet controlled by the servo, and the [__] is the slider on the outside of the box. hope this makes things a little more clear  :~

i have dabbled with the Arduino Uno i got a little, but still quite a noob in all this. this will be my first project with Arduino (if i indeed will need to use it - otherwise it will be my first electronics-projects aside from some simple circuit-bending)

any ideas, tips, do's, don'ts, whatever?


Sounds interesting, have you thought about making it MIDI controlled?
What about modifying a scanner or printer to do the movement?


Any idea of the sort of striking frequency you want to achieve? I'm envisaging some sort of solenoid based mechanism, but by the time it's got levers and hammers connected I imagine there would be significant inertia in the system which would make high frequencies hard to achieve.


Have you seen this mechanical bass?
Includes links with a paper on how it was developed.
I don't think just moving a hammer up & down the string makes a difference, you need something to pinch the string to change its length so it vibrates at a different frequency.
Unless you use the hammer to do the pinching, a la Eddie Van Halen's hammer-ons and pull-offs.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Dec 16, 2012, 03:20 am Last Edit: Dec 16, 2012, 03:24 am by rhowaldt Reason: 1
thanks for the quick answers and questions guys.

@Crossroads: while very cool, that mechanical bass is way more complex than the idea that i got. the sound i am after is derived from a way of striking a (acoustic, in my case, but should work on electric too) guitar that is maybe not so commonplace. to replicate, do as such: take some metal object (i usually use the ring that is on my finger already) and tap the high E on the position where you usually strum/pick it (dunno the name for that part of the guitar). so on acoustic, right above the opening. now continue tapping and move up and down the string. that is what i am looking to recreate here.
the tapping mechanical, the movement manual (by way of a slider). hope that clears it up some more, i understand this is sometimes hard to explain. will try and do some drawings or something...

@PeterH: i would like for the striking frequency to be able to go both really fast and really slow. was thinking with a knob maybe one of those click-knobs, where it clicks to another setting after zero, and that would be 'one shot' with a button or something. just so you can also do manual control over the striking frequency if you want to.

@Grumpy_Mike: i have thought about MIDI control but kinda feel that i want to build it with manual control first, then maybe add MIDI later. as i said, my first project, not looking to over-complicate things :)
as for the controlling of slider-movement: those suggestions are great, but i feel it would become too robotic. i am looking for a sorta mechanical-manual hybrid sorta weird instrument, and something you'd have to be able to play yourself, with your hands i mean. so i think a hand-operated slider would be perfect for that.

one thing i forgot to mention that i'm not sure how to go about is audio, and mainly the possible recording or routing of the sound this thing will produce. i like that it is analog so kinda want to avoid doing electrical stuff with pickups and such here (while that certainly would be awesome too, but, like the MIDI, maybe later :). so that means that when you want to record it, you should be able to open the top and stick in a mic (as with a piano). however, my concern would be with using a servo here: can these things be made to operate noiselessly (or nearly), especially with the break-neck speeds i want to achieve? or is this a beautiful flaw in my plan? :D

P.S. by the way, the enclosure will be one of those wooden cases for a single bottle of wine. i'd attach a tuning-knob for the string on one of the short sides.


Changing where you tap a string only affects the harmonic content of the note it produces in octaves. So there is no real frequency control.
I think your main problem is moving the striking hammer or whatever into place quickly enough.
Good luck with it.


i would like for the striking frequency to be able to go both really fast and really slow.

Um - OK. That doesn't really tell me anything though, does it, since I have no idea what you consider 'really fast' and 'really slow'?


@Grumpy_Mike: thanks :)

@PeterH: hmm yeah, you're right, sorry :D uhm well all i know about measuring speeds is BPM, so if we're going by that, just did some testing, and 200BPM would be fast enough for me :)

do you guys think it is possible to have this thing controlled by a servo going 200BPM at max, and still have it quiet enough to be able to record it?


200BPM = 3.33 notes/second, slow triplets.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Where are you going to mount the servo? How it's mounted will have a huge impact on the amount of noise it causes. The amount of weight that the servo needs to move will impact it's speed.

You're just going to have to try some stuff.
The art of getting good answers lies in asking good questions.


I'm not a musical expert but I'd have thought your technique on an acoustic has more to do with the resonance into the body and harmonics than proper tuning.

For a one string piano my thoughts would be the point that the string passes through being movable with a servo or stepper motor (like the fingers on guitar) and a fixed hammer (plucking in the same point).

In laymans (my) terms, move the 'finger' and then 'pluck' and repeat?


do you guys think it is possible to have this thing controlled by a servo going 200BPM at max, and still have it quiet enough to be able to record it?

If you still plan to have the assembly moving along the string, I imagine that'll need motors and gearing and so on which will be rather noisy. Servos would be noisy too - and not particularly well suited to sudden movements - so I would have thought a solenoid would make a better actuator.


@Paul_S: not certain about that yet. the mechanism that taps the string should be movable so i gotta mount it somewhere that it is still free to have movement along one axis... like you say, probably gonna have to try some things out.

@tack: hmm, interesting thought about making the string movable instead of the hammer. however, i think that would make the entire device a lot bigger. not entirely sure though, because i am not even sure how long the string would need to be for this to work properly. got to experiment with this a bit.

@PeterH: well, the assembly will not be moved by motors but by hand. in essence it could be quite a simple slider-thing, but of course it would have to move along some type of rail or something. however, don't think that would have to be noisy.
thanks for pointing out that servos aren't too well-suited to sudden movements. i didn't know that. in fact, i simply thought of a servo because that is the only thing i know of that makes things move mechanically with applied power. i had to Google for 'solenoid'... but that does sound interesting. thanks again, that might be a better method indeed.

any tips on how to approach this? or should i stop asking and start building? :)


Surely it can't be any longer than what you've already proposed with the moving hammer, but should give proper control over the tuning.

It's the length and tautness of string that will determine your overall range, which will always be limited with a single string anyway.


Dec 16, 2012, 08:13 pm Last Edit: Dec 16, 2012, 09:25 pm by Grumpy_Mike Reason: 1
I made a harp player out of the read / write motor from CD drives. Now it was one motor per string but is gives you and idea of an alternative plucking mechanism.


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