AVE…
My good friend sent to me a E-mu ST 1200 service manual. We analysed its design and came with clever way to make velocity pads for any MIDIBox with at least 8 AIN ports.
The basic version utilises one piezoelectric membrane as velocity/pressure sensor and 8 microswitches for AIN pin selection.
Circuit diagram:
It’s just an amplifier/filter. RV1 is used to set pad sensitivity.
Construction:
Two piezoelectric membranes connected in parallel are between two metal or plastic bars, which are loosely joined together. On top are placed microswitches. Tapping one of them will send a pulse generated by membranes and amplified by circuit to one od AIN ports. This is the simple, yet working way…
In more complex design you can use DIN imput(i.e. push-button 4x4 matrix) to force the Core to read data from AIN ports. Still at least one membrane must be beneath the buttons. This way you can eliminate adding contacts noise from microswitches.
If you want to make a real dynamic keyboard, you must have original mechanical keyboard assembly from piano or something like that. Just replace strings with piezoelectric membranes and switches BENEATH them, so when hammer strikes any of them, you can get real velocity parameter. Switches should be connected to DIN module and write proper code for Core module…
This is just concept. I wasn’t able to test it, but I’m sure it will work.
TLC27M4 should be replaced, since in some countries(i.e. in Poland) is impossible to find it. Probably any op-amp should work with this design…