We're developing a new version of Spresense e-violin.
From this version, we try to automatically tune the strings.
As a trial, we attached a single DC motor to pull one string. We also attached piezo pickup, connected to Spresense. The sampled sound is FFTed and the estimated frequency is used to adjust the tension of the string.
In near future, we expect to control four motors by this 3D-printed motor box.