Second revision

Fixes issues with v0.1 boards:

• GPIO15 pull-down resistor is added to the PCB layout
• Orange Pi 4 variant's BoM now lists the correct LCSC part number for the UART resistors

Initial revision

Known issues:

• Missing pull-down resistor on GPIO15. Needs external resistor as can be seen in the pictures.
• Orange Pi 4 variant's BoM lists wrong LCSC part number for the UART resistors, ordering SMT assembly from JLC without correction results in UART data corruption. Schematics are correct.