revisions from v1:
- incorrect footprint for 1/4'' jack (can make it work)
- 7 segment displays can be closer together (footprints are exact)
- usb diode array wrong footprint (sot666 should be sot23-6) [or order the correct footprint works too]
- remove 1.3k ohm resistor on Vcc of optoisolator
- remove grounding resistor (and ground connection) on pin 2 of the midi DIN
- deisolate potentiometer rv3's ground island
- add silkscreen text to the boot and enable buttons
- add silkscreen text on the back detailing dimensions for board and holes
- enable pin on esp32 needs a 10kohm pullup resistor and a 1uf pulldown capacitor, separate from the button circuit
- remove 22 ohm in-line resistors on d+ and d- usb lines (o ohm resistor recommended by the datasheet)
- probably remove the decoupling capacitors on the usb lines too
- breakout i2s interface
- buy 0 ohm resistors
- you can afford a lot more room between chips and components (besides power capacitors)
- somethings funky with op-amp U4 (it gets hot when powered). also add trimmer potentiometers to tune its gain
- actually follow the datasheet for the pcm5102 man
	- 2.2nf instead of 2.2uf capacitors on the l/r audio out lines
	- tie mute pin directly to power source
	- theres a whole pcb layout section for TI chips
- soldering tip: chips always go first