Specification
Project Overview
Draft bare-board STM32F756 controller for RTK and two LiDAR devices. Initial scope: electrical capture; physical layout and manufacturing release require further approval.
Intended Use
Sensor-interface and on/off control board. Deployment environment, cable lengths and production quantity remain unspecified.
What the Board Should Do
- Read an MCP9808 temperature sensor over I²C.
- Blink eight individually controlled onboard LEDs.
- Provide three GPIO-controlled on/off MOSFET channels.
- Communicate over three separate 3.3 V UART TX/RX interfaces: RTK, LiDAR 1 and LiDAR 2.
- Protect external UART signal lines against ESD; miswire/surge requirements remain open.
Main Features and Hardware Subsystems
STM32F756 MCU with required supply support, reset, boot configuration and SWD programming access; MCP9808 sensor; eight LED/resistor branches; three reserved switch-control signals; three protected UART interfaces; two DC/DC supply branches.
Mechanical System Architecture
Bare PCB. No enclosure requested. Board dimensions, mounting holes, connector orientations and UART connector families are not yet defined. Input uses a two-pin Molex Micro-Fit 3.0 board connector; exact board-side variant to be sourced.
Electrical System Architecture
24 V input connector → input protection → parallel 5 V and 3.3 V conversion branches. 3.3 V → MCU, temperature sensor and LED circuitry. MCU → three protected UART TX/RX pairs and three reserved switch controls.
Interfaces and Connections
- Input: nominal 24 V DC, two-pin Molex Micro-Fit 3.0.
- I²C: MCP9808; local sensor, pull-ups to 3.3 V.
- UART: three independent 3.3 V logic TX/RX/GND interfaces, not RS-232 or RS-485. Specific RTK/LiDAR models, baud rates and cable lengths pending.
- Debug: SWD and reset access.
- Switches: three MCU GPIO controls; actual MOSFET power stages deferred pending load voltage, continuous/inrush current, load type and high-side versus low-side requirements.
Power and Runtime Expectations
External 24 V supply; no battery or charging requested. Input tolerance, transient environment and total external-device power demand remain unknown.
Power Tree and Power Budget
- 24 V → Hi-Link K7805-2000RL → 5 V.
- 24 V → TI LMR50410XDBVR → 3.3 V (explicit user decision: not fed from 5 V).
- 3.3 V supplies controller, sensor and LEDs.
- RTK/LiDAR supply delivery and rail currents are not specified; do not assume these devices can be powered by this board.
- Component limits, passives and thermal margins must be checked against sourced datasheets during capture.
Manufacturing and Assembly Expectations
Prefer LCSC sourcing. Assign verified symbols and footprints; do not silently replace specified active components. Layer count, assembly process and manufacturing release remain pending.
Firmware-Relevant Hardware Requirements
Configure I²C temperature reads, eight LED outputs, three safe-default-off switch controls and three independent UART peripherals. Preserve SWD access. Sampling rate, baud rates, timing and firmware deliverables are not yet defined.
Physical Design Expectations
No PCB placement or routing in the initial capture scope. Reserve space for the selected power module and connectors only after their geometry is verified.
Important Design Decisions
Use parallel 24 V-fed converters, not cascaded conversion. Use a practical STM32F756 package with sufficient GPIO and verified UART alternate functions. Do not finalize load-dependent MOSFETs or device-specific connector pinouts without load/device data.
Assumptions
Eight LEDs are onboard low-current indicators. UARTs require TX/RX only, without flow control. UART connectors carry common ground; no external device power is connected until confirmed. Initial UART protection covers ESD, not sustained 24 V miswiring.
Open Decisions
Exact RTK/LiDAR models; UART baud rates/cable lengths/connectors; three load ratings and topology; input voltage tolerance/transient severity; board dimensions and mounting.
Change Notes
Initial requirements captured from conversation. Confirmed Hi-Link K7805-2000RL and direct 24 V input to the LMR50410XDBVR. No persisted Specification existed when inspected.
Latest Required Correction and Capture Status
The user explicitly requires STM32F756ZGT6, not the STM32F756VGT6 selected during initial capture. The existing U1 was reported as STM32F756VGT6 (LQFP-100); replacement with the requested ZGT6 and a complete package-specific pin/power/alternate-function review are not yet performed. Do not use the captured footprint or physical pin numbers for fabrication. Verify ZGT6 package and geometry from ST documentation before replacement. Preserve intended GPIO signal names only where supported by the requested part.
External devices are now confirmed as two Benewake TF-02 Pro LiDARs and one Unicore UM982 RTK. Whether UM982 is a bare module or carrier remains unknown. External devices are not powered by the current capture.
The initial capture contains a reported 67 components and 48 nets in 11 functional groups. Logical connectivity exists; visual schematic wires and arrangement, PCB placement and routing were not performed. The 5 V module branch is absent: the exact Hi-Link K7805-2000RL could not be verified in the library or search, and no substitute was made. Ask for a label photo or datasheet to resolve the exact suffix.
An independent electrical review was started but no review result was collected before execution stopped because ACUs ran out. The latest MCU correction was acknowledged but no replacement or reconnection was performed.