Finally, I completed version 1 of my scalp massager. It consists of 15 programmable 12mm vibration motors mounted on to a BraiNet Placement Cap.
The vibration motors are soldered and hot glued onto an Adafruit JST-PH 2-Pin SMT Right Angle Breakout Board which is then connected to a JST extension cable and hot glued onto the Brainet Cap.
The heart of the massager is an Adafruit Metro Mini Arduino processor. The JST extension cable is wired to a protoboard and wired to the Metro Mini. All the ground cables are soldered to the ground rail and the positive (red) wires are mounted to the output pins. I ended up wiring the motors to pins 2-13 and used pins A0-A2 as output pins for a total of 15. By avoiding pins 0 and 1, I'm able to program the Metro Mini without conflict.
While I'm in the early programming stage, there are sequences that vibrate one side of the scalp then the other. Another sequence revolves around the scalp. And yet another vibrates the symmetrical points on either side of the scalp. I'm still experimenting with different sequences.
Version 2 is already underway using 21 motors and this time using an Adafruit Bluetooth Feather processor, so I can develop a smartphone interface.