i will start the prototyping with ST’s development board NUCLEO-H723ZG. it allows to test most ( not all ) features and peripherals. PS { the boards connectors need to be equipped with double-row pin headers first … grrrmpf }

i am still struggling with one fundamental decision and that is whether i should produce smaller PCBs ( e.g for external memory BGA-24 IC ) and test them individually or if i should just take a leap of faith and design the entire board, planning 1–2 revision rounds. hmmm, difficult …

these are the sections or modules i want to test:


  • STM32H723ZGT


external memory

  • BGA-24 memory (APS12808L-3OBM-BA)
  • Octo-SPI/HyperRAM™ interface
  • not sure how to test the BGA-24 memory IC? to just have this manufactured as a PCB seems a bit excessive

battery + power supply

  • test charging circuit (TP5400)
  • with Lolin D1 Mini Battery Shield
  • test with battery type 18650
  • can the circuit charge and supply power simultanously?
  • do we need a hardware on/off-switch? or can this also be done in software?
  • with PCB mounted holder e.g MY-18650-01

on/off switch

“just thought that when we have a battery on board there might be the need to be able to switch the power supply on or off”


  • are 2× USB-C connectors required or would a single one work?
  • one for charging or power supply
  • … and one for USB Device/Host where it could also power the board when connected as a ‌USB Device

audio codec


  • test 4-bit wide SDIO/SDMMC interface
  • test card detect functionality


  • DAC(1×)+ADC(3×)
  • connection to modular synth?!?
  • 12V tolerant ( or modular connection as extension board = 0.0—3.3V > -12.0–12.0V + -1.0–1.0V>-5.0>5.0V(?) )



  • what layout?
  • maybe case with fake shrouded connectors ( see IDC housing )
  • only 2 LEDs ( with PWM )


  • reset, boot, programmer

mechanical keyboard keys

  • just below encoders?

programmer interface

  • STD14
  • pogo pin connector ( without housing on front-side )

case + shape

  • switch?
  • portrait mode?
  • something unique!!!
  • hole for a strap
  • black&white PCB