DESCRIPTION

We have designed a small pcb using ST's STM32L4S9 Cortex M4F MCU as a test bed to develop a fast (120 MHz), low-power (~3 uA sleep) microcontroller whose internal 2 MByte flash and 640 kByte SRAM can be augmented by fast, low-power external QSPI flash and SRAM. The primary application is FFT analysis of audio/ultrasound data, but any application that needs a lot of GPIOs and/or a lot of fast memory for number crunching in a small, low-power device will benefit.

We chose the STM32L4S9 because it comes in a 10 mm x 10 mm, 0.8-mm-pitch, BGA-144 package. This means it is small enough to fit onto a "standard" 0.7 x 1.4 inch development board, the board design is amenable to using inexpensive 4-layer pcb construction and OSH Park design rules, and it is easy to hand-assemble the MCU using low-temperature solder paste and a hot air gun or rework station.

The STM32L4S9 development board is programmable via USB using the Arduino IDE for maximum ease of use.

https://hackaday.io/project/168095-stm32l4s9-development-board-with-external-sram