Piezo - MIDI Vulcan Harp?

[G.S. Monroe]

I have a concept project I'm working on, a crazy notion but I think it should work if I can sort out the details.
Question #1: How many separate feeds (strings) will typical MIDI software support?
Question #2: Does the signal from a piezo sensor require processing through a circuit board or will MIDI software "read" analog signal coming through a 13 pin connection?

I was discussing Hexophonic guitars with a friend, as we were watching YouTube videos demonstrating the abilities of MIDI guitars when the idea came to me of doing an 18 string MIDI Vulcan Harp. The original TV series used some exotic (at the time) audio effects to give Spock's Vulcan Harp a Sci-Fi sound. I believe it is possible to make this a reality by mounting individual string rod piezos at the string "Fret" positions along the upper support arm and running the wiring harness down the arm to the body and the internal electronics and controls.
(hopefully there is a Star Trek fan that knows what I'm saying). Since having 3 parallel Ghost systems would be price prohibitive, I'm wondering if there is a simpler wiring option and use MIDI software for handling the processing.

[Mark Swanson]

Well, a keyboard has MIDI output, so obviously MIDI can handle all the notes on a keyboard so it'll do 18 notes. And, it is a big plus if you are not fretting the notes, and just using them as a standard harp. This limits you to 18 notes total but also makes the MIDI side of things much easier. If that's all you want to do is trigger MIDI notes on and off, then maybe you can steal the guts out of an old electronic keyboard with MIDI out.

[G.S. Monroe]

Interesting idea, I thought that MIDI keyboard keys were basically on/off switches. Will the circuit carry analog (string tone) vibrations?
I'm wanting to basically expand upon the Hexophonic guitar concept, having each string piezo on it's own channel and using MIDI synth to modify the acoustic string output, kinda like autotune.

[Mark Swanson]

They are just on/off switches, I thought that's what you wanted. If you want piezos too that greatly complicates things. If I were you, and I am not, I would just stick with MIDI. You have a ton of cool options there, while the actual acoustic tone of such an instrument may not be very good, and if you just plan on making an electric instrument then you don't need to worry about any acoustic tone in your design. Still, there are harp designs on the web that show you how to place a piezo under each string, and this could be done. Then you'd need to just use two outputs, because a circuit that would mix and send analog and digital information down the same cable would be a real trick...like what the Ghost system does.

[Hans Bezemer]

Greg,

What is it exactly what you want? A digital instrument with on/of switches or a analog instrument with a opportunity to convert the signals to midi?
Keep in mind that converting analog audio to midi always introduces some latency in your signal.
There a several other ways to create a polyphonic pickup.
You could check this: http://www.mimf.com/phpbb/viewtopic.php ... hexaphonic
Currently I'm about to experiment using my strings as moving coils. This will result in a polyphonic pickup.

[Jim McConkey]

One thing to keep in mind when trying to use an old keyboard is that the keyboard on nearly every MIDI instrument for the last decade or more has aftertouch, which means that every physical key operates two switches per key in quick succession. You won't get any output, or worse, stuck notes, if you operate either switch without the second being closed in short succession. Nearly every MIDI keyboard is therefore unusable for simple switch instruments. I have an old set of bass pedals with a set of single switches that I want to MIDI-fy, and initially started on this route, but quickly ran into the aftertouch issue. There are a couple really old mini MIDI keyboards that could be used, but you have to get lucky enough to find one. I haven't been lucky enough yet. Time for a quick PIC controller design!

[Andy Gleeson]

I would go for a micro controller interface with a couple of port expanders to handle all the string inputs. Look at the Arduino project there is a midi library available for it.
BTW midi only handles digital messages, as far as I know you cannot use it to send analog data.
midi will handle velocity info so you could use piezo sensors to convey what is effectively volume info.

Apologies for disjointed English, trying to type this on the phone.

[Jim McConkey]

Not analog, per se, but MIDI can send continuous controller data, which is digitized analog. I know it will send 8-bit data. I haven't looked in a while, but I believe there is also a 16 bit format as well. What MIDI will NOT send is digitized audio.