• STM32G031G8U6 MCU, IMU, CDC, analog multiplexers, RS-485 transceiver, local regulation, SWD pogo pads
• 18 capacitive sensor-pad electrical interface using three 8:1 multiplexers and one FDC1004 CDC
• Schematic notes and net labeling supporting flex stiffened-island implementation

• Final PCB placement and routing
• Firmware implementation details beyond interface assumptions

• 5 V input rail and ground from shared bus harness
• RS-485 A/B shared half-duplex communication bus
• SWD pogo pads: SWDIO, SWCLK, NRST, 3.3V, GND
• 18 capacitive sensor pads into three multiplexers

Diagram

• The board shall acquire 18 capacitive tactile channels as a 6 x 3 matrix using one FDC1004 and three TMUX1308 multiplexers.
• The board shall acquire 6-axis inertial data from the ICM-42688-P over SPI using an interrupt-capable connection.
• The board shall communicate over a shared half-duplex RS-485 bus using master-polled node responses.
• The board shall support SWD-based programming and debug through pogo pads.

• Input power: distributed 5 V bus
• Key rails: 5 V input, regulated 3.3 V local rail
• Critical interfaces: SPI IMU, I2C CDC, UART to RS-485 transceiver, shared mux address lines A0 A1 A2
• RS-485 termination shall be present only at bus ends using nominal 120 ohm matching to cable characteristic impedance
• Unused mux inputs shall be tied to ground to avoid floating capacitive nodes

• Low-profile flex PCB band node with active components on a stiffened island
• Bend zones shall remain free of components and vias
• Large or strain-relieved pads should be used for bus wiring and sensor-line transitions in later layout work

• Moderate latency is acceptable; reliability and debug visibility are prioritized over high sample rate
• Keep external interfaces protected: RS-485 A/B requires ESD protection
• CDC and mux signal paths should avoid floating nodes and preserve low-noise grounding
• Schematic should be organized into clearly labeled functional blocks for flex-integration handoff

• Firmware must schedule mux stepping, FDC1004 conversions, IMU reads, and RS-485 framing
• Mechanical integration will define final pad style and bend-zone geometry

• Parasitic capacitance from textile wiring and motion may reduce tactile signal margin
• RS-485 termination must not be populated on mid-bus nodes to avoid overloading the bus

• Schematic contains STM32 MCU, SPI IMU, I2C CDC, three multiplexers, RS-485 transceiver, ESD protection, SWD pogo access, and 5 V to 3.3 V regulation
• Functional blocks are clearly separated and named for sensor node bring-up and debug
• RS-485 end-only termination strategy is documented in the schematic notes and component roles

• Verify net-level wiring against datasheet pin functions for MCU, IMU, CDC, muxes, and RS-485 transceiver
• Review for missing decoupling, floating pins, and incorrect bus wiring

• Updated schematic
• Updated BOM
• Project specification and design notes

• RS-485 termination resistor is intended only for bus-end variants and should be DNP on intermediate nodes
• SWD pogo pads are required for firmware flashing and initial bring-up

• Repurposes the project into a flex-band sensor node architecture
• Adds CDC plus analog-multiplexer tactile front end and SPI IMU requirement

• Final choice of 3.3 V regulator footprint and current margin for the flex node
• Final mapping of 18 sensor pad names and any shield usage on FDC1004 in revision 1