mimic guitar strings strumming: piezo or capacitive

[fenicento]

Hi everyone,
for my Yet Another MIDI Guitar Project © I would like to mimic strings strumming without having physical strings. Still, I would like to have something to hit with my fingers, possibly with a decaying amplitude response.

My first option is to use 6 piezo sensors like this one:

covered with a rubber / silicone cover. The problem I see is that even touching just one of the sensors, the others would still sense some vibrations. Maybe playing with thresholds would be enough to have a good result, but I'm not sure.

The second options would be to have capacitive sensors, which would probably be easier to implement (maybe with an external controller like the MPR121 since Teensy 4.1 doesn't have touch inputs), but I would have to play a bit with the input signals in order to simulate a reasonable decay.

The reference is the Artiphon Instrument 1. I don't understand what they are using, but looks like it works fine:

https://www.youtube.com/watch?v=GSD9UlvCl4M&ab_channel=Artiphon

What would you recommend? Thanks!

edit: I just realized that the best section of the forum for this thread is "Project guidance", sorry :/

 

[fenicento]

Bump

or could anyone at least tell me what is the most convenient way to use a piazo with the teensy analog inputs? I found this scheme that seems to work:

but I would lie to add something to smooth the amplitude wave. Any suggestions?

 

[Deleted User]

The piezo thing would work. Just be aware the piezos can produce an infinte voltage (from the MCU point of view), so it is important to have suppressor diodes with the voltage corresponding to the MCU supply, in the Teensy 4.x case 3.3V, to not fry the MCU. High pulses could easily crosstalk (burn) through the internal crossbar, that is why the signal is on all channels.
The resisor R1 is to discharge the piezo once it is silent. This also helps against ageing of the piezo due to overvoltage charge buildup.

If there is mechanical crosstalk, then it makes sense to separate the sensors from each other, by buffers and an inert heavy mass inbetween.

The Teensy 3.6 has much faster ADC than the Teensy 4.x, so maybe 3.6 could do this job better.

Piezos tend to be noisy in a mechanicaly stressful environment, so maybe a threshold could separate the signals and prevent false triggers from touching the instument alone.