Design motherboard v1

[chiplet]

General:

• [x] choose microcontroller STM32F303RE
• [x] board schematics
• [x] board layout

Power Supply:

• It's probably best to use a separate power supply for powering the electromagnet coils and the control circuitry to avoid EMC issues
• [x] regulate required voltages from an external wall wart
  • [x] 3.3V for the microcontroller digital logic
  • [x] 3.3V microcontroller analog reference

Interfaces:

• [x] JTAG
• [x] ST-LINK/V2-1 debugger
• [x] stack connector(s) to electromagnet driver board

TODO:

• [x] Logic level conversion from mcu to RGB

[chiplet]

MCU selection:

• All analog circuitry (photo gate sensors) shall convert their measures to digital format so the microcontroller does not have to deal with analog signals.

MCU requirements

• [x] Enough GPIO pins (at least to support for adding IO expansion for all required signals)
  • segment indicator LEDs (16)
  • motherboard RGB (1)
  • driver board RGB (1) (can be chained with motherboard RGB)
  • electromagnet control signals (16)
  • debug UART (2)
• [x] UART
• [x] QFP package

The application is not very demanding so pretty much any reasonably sized MCU will do the job. If the I/O lines run out, adding more with expansion modules or shift registers is very easy and can be done without degrading device performance. STM32F303RE is reasonably priced and has extensive analog peripherals if they are deemed necessary in the future. Additionally there is a nucleo board available which can be used as a programmer and makes it easier to get started with firmware development.

[chiplet]

GPIO expansion considerations

Segment indicator LEDs can be driven with the control signals without much issue. A good solution would be to use a LED driver IC with 16 outputs and serial control interface, or maybe even a shift register.

IO expansion ICs allow for bidirectional I/O. This is not necessary for the segment indicators, but would be useful for reading sensors.

Shift registers: SN74HC595 is currently used for prototyping. These can be chained so 16 indicator LEDs can be controlled over a serial connection with 3 lines in total.

[chiplet]

MCU Implementation

TODO:

• [x] Copy reference design from STM32F3 hardware development app note

[chiplet]

First revision design is complete!