wav audio player

• MP3 decoder chip

• transistors to enable/disable peripherals

• display

• addon (SAO) header

• battery power

• uart output header

• expose some gpio pins to a header

• smaller mounting holes

• connect SWO pin for jlink debug messages

• headphone jack/driver

• SPI pins on flash are backwards

• ground and test points

• Went exlusively with JLCPCB parts and paid for assembly service
• Removed lipo circuitry, sd card and hall effect sensor
• Added spi flash to store music
• Removed FTDI went for a direct USB connection to the STM32
• Changed to a smaller stm32f405
• Reworked output stage to include a digital potentiometer
• Significantly reduced size of board
• Went to a 4 layer pcb