Simple designs make hardware customization easy
Small, inexpensive development boards that provide access to all of the STM32L4 peripherals are great, but the simplicity of the hardware designs makes for easy customization for specific applications.
We have been using the STM32L433 and STML432 for custom designs and letting these drive Arduino core development priorities. Here are a couple of examples:
This board uses an STM32L433 as master to several slave sensors to detect and process signals from industrial equipment and report to a remote server via blue tooth (module not mounted). The board can get power through the USB cable or a LiPo battery, and a battery charger is integrated into the design. Since this is a prototype used for application development, we have exposed most of the pins of the STM32L433 for diagnostics and for adding additional components. The small footprint and modest component requirement of the STM32L433 allows great flexibility in board size, shape, and placement of necessary sensors, memory, and radio modules in the design.
The next example uses the STM32L432 as master to other MCUs:
The STM32L432 receives quaternions from the EM7180, which itself is master to the motion and pressure sensors, GNSS data from the CAM M8Q, then processes and packages the data and sends it to the ESP8285 via UART bridge for transmission to a hand-held controller. The STM32L432 also receives flight control instructions from the hand-held controller and adjusts the motor drivers via PWM to keep the flying robot (AKA quadcopter) in stable flight in the desired direction.
A previous version of this flight controller used the 80 MHz ESP8285 as master with an FTDI FT230XQ as USB-to-UART bridge for USB programming and serial output. The 80 MHz STM32L432 also enables USB programming and serial output, but doesn't suffer from the overhead of wifi management, allows efficient fusion of the GNSS and IMU data using its FPU, and provides flight control update at a 1 kHz loop rate. The small STM32L432 package and simplicity of its hardware design make autonomous, trajectory-following flight in very light (< 50 g) UAVs a reality.