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The Objective

Off-the-shelf development boards are expensive and misaligned with the team’s specific STM32 MCU architecture. This custom 4-layer board maximizes GPIO access while bringing out the specific pins to be compatible with Arduino Shields. The cross-compatible nature allows for quick sensor testing, embedded knowledge transfer, and firmware development before the final data acquisition boards are manufactured.

System Architecture

The architecture serves to transition the team from STM32F1 microcontrollers to a higher performance STM32F7 series or similar MCUs with ethernet capability. The upgrade provided the necessary pin density for the current requirements while having plenty of bandwidth for future hardware design improvements, the biggest of which will be Ethernet capability. To maintain budget controls and consolidate the Bill of Materials (BOM), passive components and power delivery components were standardized using JLCPCB’s basic component library, eliminating extended part placement fees while maintaining >80% power conversion efficiency.

Design Rationale & Challenges

Routing a dense, full-pinout development board required strict adherence to signal integrity principles. To prevent high-frequency ripple from coupling into communication lines, (like USB 2.0 and CAN) differential pairs were strategically routed on the opposite of the MCU, opposite the high-speed oscillator. The impedance-matched USB lines proved spatial and navigation challenges. The trance width was thicker than the CAN traces which meant routing through tight clearances while trying to minimize the length required some strategic rerouting and component placement. Conversely, CAN bus routing was made relatively easier by placing transceivers near the edge of the board.

The final challenge came during the board assembly process. A GPIO pin when being placed into the board sheared a copper barrel that’s placed in PCB holes for conductivity, and attachment. This shear ripped up the trace that the barrel was attached to. The connection was restored with a hand soldered bodge wire. Everything proceeded to work as expected when testing conductivity signal integrity through the bodge wire.

Outcome & Validation

The board successfully served as the primary hardware testing platform for the electrical and software subsystems. This allowed new members to quickly learn embedded firmware, as well as get hands-on experience programming, testing sensors, and getting comfortable with the team’s electrical infrastructure. Clock functionality and thermal stability were validated in multiple environmental states using test code, multimeters, and oscilloscopes, ensuring the MCU maintained reliable timing for data acquisition tasks.

Technical Specifications

• Core MCU: STM32F7 (ARM Cortex-M7)
• Architecture: 4-Layer Mixed Signal
• Interfaces: CAN, USB 2.0, JTAG, SPI/I2C/UART
• Tools Used: Altium Designer, JLCPCB, STM32CubeMX, SolidWorks

System Block Diagram

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Power Delivery Network

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MCU & Differential Interfaces

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Board Routing

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