Norwegian-based Tenko has released an open-hardware development board based on STMicroelectronics’ STM32C5 microcontroller family. The compact board follows the familiar Blue Pill form factor while adding USB-C power, onboard USB-to-UART connectivity, and an alternative firmware environment based on Oberon-2.

The board uses the recently introduced STM32C551CE, a 32-bit Arm Cortex-M33 microcontroller operating at up to 144MHz with 512KB of flash and 128KB of SRAM. The MCU also includes an FPU, DSP instructions, an 8KB instruction cache, dual 12-bit ADCs, a 12-bit DAC, a CORDIC accelerator, and multiple timers and serial interfaces.

Measuring 53.5 × 20mm, the board uses two 16-pin headers for breadboard-friendly prototyping. It includes a CH340E USB-to-UART bridge connected through USART1, a USB-C power connector, 24MHz HSE and 32.768kHz LSE crystals, a 3.3V LDO, reset and user buttons, status LEDs, and an SWD header for programming. Most remaining MCU signals are routed to the edge headers.

STM32C55xxx block diagram

The design was created with KiCad 10, and the project repository includes the schematic, PCB layout, pinout, assembly drawing, footprints, and fabrication files. Tenko notes that other LQFP-48 STM32C5 variants may also be usable as they become available, provided they remain pin-compatible with the current layout.

STM32C5 eval board demo

For conventional development, the repository includes a CubeMX2 project that can generate a CMake-based STM32 project. The board has been tested with the USB-to-UART interface, LEDs, buttons, and onboard crystals.

The project also supports an alternative firmware workflow through ECSMicroLib and ECSOberon, an Oberon-2-based language environment for embedded systems. ECSOberon adds features such as manual memory allocation, unsigned types, variable pointers, packages, and basic templates, while retaining Oberon’s module-based structure.

STM32C5 eval board

ECSMicroLib provides MCU-independent interfaces for GPIO, RTC, I2C, SPI, UART, and OneWire, along with several peripheral drivers and coroutine support. Current supported boards include the STM32C5 evaluation board as well as several STM32F4 and STM32L4 development platforms.

The project documentation notes that the current hardware revision has a few known issues. SWDIO and SWDCLK were swapped, and the silkscreen was difficult to read. Tenko plans to correct these in a future revision and is also considering exposing BOOT0 through a test point and adding a jumper to disable the power LED for battery-powered applications.

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