Mod my upright piano

July 27, 2016 7:46 AM

Yesterday I rescued an abandoned Érard piano from the streets. Its innards had been removed, but it has all 85 of its original keys (it's an 85-key piano). I would like to be able to use it as a synthesizer, since I can't afford a new soundboard for it. The online DIY synthesizer world is so full of resources, however, that I am at a loss where to start.

First and most obviously, I would like to play whatever synthesizer I hook up to it through the keyboard. I do have basic, though rusty, electronics skills, including soldering. I am able to read circuit diagrams. How would I wire up wooden piano keys to create a MIDI keyboard? Everything I've found so far assumes rebuilding an already-electric keyboard. My budget is tight at the moment, but it looks like a project that wouldn't cost much if done from scratch?

Do feel free to say whether this is realistic as well. Ideally I wouldn't want to modify the keys irreparably, but this is my classically-trained pianist and granddaughter-of-carpenter's heart speaking. They're beautifully weighted.

Following from the MIDI keyboard, DIY synth possibilities are endless. I'm able to find plenty of resources for those, though anything that particularly stands out would be great to hear about. Polyphonic preferred, for obvious reasons; also I really like analog, and rich, hefty sounds. I have a RaspberryPi.

posted by fraula to Technology (9 answers total)

A friend told me that electronic keyboard keys are wired using a matrix, similar to how computer keyboards are wired. It sounds like it would be easier to remove the existing keys and store them, then use parts from a manufactured electronic keyboard of your choice. There are keyboards with weighted keys, but they are more expensive than non-weighted keyboards.

If it were me, I'd build (or place) a computer inside the piano carcass and run softsynths through a host or DAW program. If the top flips up you could conceal a monitor inside that could lift up when you're using the machine and be hidden when you're not. You'd still have to have a mouse and computer keyboard though.

It kind of sounds like you'd like to walk up and play though, rather than having to take the time to boot a computer and load programs.

I'd probably go the route of using a new keyboard. The wiring and soldering required to use the original keys sounds quite laborious to me, but even if that were trivial I'm not sure how you'd deal with generating velocity and key after touch data from a DIY solution. You'd also not have a pitch bend or modulation wheel, which expand the expressive range of most if not all synths.
posted by under_petticoat_rule at 8:06 AM on July 27, 2016

Best answer: What a lovely project!

Totally doable.

Quick cost estimate: You need 85 sensors, such as these. So €6.00 * 85 = €510 !

Then maybe another €100 for additional electronics. Speakers are such a wide price range; I'll let you estimate that yourself.

Piezo sensors might will be less expensive, not sure if they'd give you enough sensitivity.
posted by at at 8:23 AM on July 27, 2016 [1 favorite]

Response by poster: under_petticoat_rule you bring up some great points. I should add some details:
- I actually already have a digital piano, a Korg SP-250 (don't want or need to put it in the upright's carcass).
- Can't really put another keyboard in the upright's carcass without getting rid of the key pins. There is room beneath the keys to put in sensors etc. and plenty of room in the cabinetry to put in other stuff (such as a modulation wheel).
- Because of the above, for this idea, I wouldn't mind having simpler action. I do indeed want to just flip a switch and be able to play it.

On preview: also already have speakers, an amp, and an audio/MIDI interface :) thanks for the sensors!
posted by fraula at 8:27 AM on July 27, 2016

Since you have at least some of the key mechanisms still (I can't tell from the photo whether the hammers are intact?), it might be enough to just have the hammers or key pins strike something else in place of strings, like an array of force-sensitive resisters, then process those readings. Of course, that would also require 85 GPIOs and a considerable amount of software.
posted by fifthrider at 8:40 AM on July 27, 2016

Best answer: This instructable describes how to get a USB MIDI controller together with mostly off-the-shelf stuff and easy assembly, with relatively low cost. You have a variety of options on how to get the piano keys to trigger the digital events, but it could be something as simple as a small flat button under each key. Even if you don't use this scheme, the Teensy USB is a good bet to look into.

One thing to decide on early on- how important is it to have velocity sensitivity in the final product? That seems harder/more expensive, but demanding that is also completely understandable.

Also you could post this question on reddit's /r/synthdiy and possibly /r/synthesizers and probably get good results.
posted by SaltySalticid at 9:15 AM on July 27, 2016

Best answer: Velocity sensitivity is very important for a piano. Otherwise, it's an organ.

The piezo disks cited earlier are an excellent start.
You'll get a voltage impulse that is proportional to the strength of the impact:

"The electric level of the pulse is dependent on the mechanical impact force and generates about 0.001 to 40 volts. The waveform is sinusoidal decaying. The pulse duration is between 3 and 20 milliseconds and is dependent on the duration of the mechanical impulse (shock, friction, reflection)." (from http://www.v-drumtips.com/piezos/).

The challenge comes between the hammer and the input port on your Pi.
How do you digitize so many keys, cheaply?
A bakery of Pi's? (no)
An phalanx of data acquisition boards? (no)
A forest of analog multiplexers, just fast enough to get the sample rate you want? (maybe)
A swarm of 22 $0.75 PIC12F1572, that digitize, timestamp, and buffer for the Pi? (perhaps)

Nice problems to have :-)
posted by the Real Dan at 9:44 AM on July 27, 2016

Response by poster: Re: hammers and other piano mechanisms – no hammers or anything else, just the keys (pic). So I've been pondering triggers as well, the keys need a bit more resistance to be less organ-like (though they are quite weighty as is).

Somewhat tangential – it seems to have been gutted to look like a real piano while being used as a cabinet; there are shelf supports inside of it.

Have loved all your ideas so far.
posted by fraula at 10:12 AM on July 27, 2016

I'd buy a suitably sized USB/MIDI keyboard, take the case off, work out how to make it fit where the old keys are now. Then I'd work out how to fit sound modules in the gubbins of the piano where the strings and hammers were. I'd throw the old keys and mechanism out.
posted by w0mbat at 4:01 PM on July 27, 2016

Best answer: Well, if you're all right with organ performance, you might use something like an $0.14 TCS40DPR, a digital output hall effect sensor, with tiny $0.02 magnet on each key. If you want to sense velocity, stack two of them, with a spacer, per key, and look at the timing between the pulses.

I pretty much assume a swarm one dollar PICs.

Spend about ten bucks on a few keys worth of parts, and prototype them. Often while you are working with a cheap prototype, better methods and materials are revealed.
posted by the Real Dan at 11:54 PM on July 27, 2016