• 12 V power input and star-ground entry
• PCA9685-based PWM/control distribution
• Five low-side MOSFET load drivers for RGB LEDs and two chamber fans
• One low-side MOSFET relay driver for K3
• Two A4988-based stepper motor driver channels
• REF195-derived 5.000 V analog reference output for ADS1256/sensors
• Isolated 24 V PELV feedback using three optocouplers
• RTC and SD module interfaces
• External connectors J1 through J12 per TRIBO-ELEK-012

• PCB placement/routing optimization
• Resolution of all TBD items in the originating specification
• Functional safety certification for K3 path

• Power input: +12V and GND at J1, +3V3/+5V/I2C/IO_B4 at J2
• SPI and logic interface: J3 to ADS1256 and SD module
• Analog/instrument harness: J4 with +5V, SPI, DRDY, and +5V_REF
• Chamber power/load interface: J5
• Stepper motor power stage outputs: J6 and J7
• Stepper logic control: J8
• TEC PWM/dir signals: J9
• K3 relay output: J10
• Isolated 24 V input side: J11
• 3.3 V logic feedback output side: J12

Diagram

• The board shall provide a PCA9685 PWM controller at I2C address 0x40 with VCC at 3.3 V and V+ at 5 V.
• The board shall drive five low-side MOSFET outputs for LED_R, LED_G, LED_B, FAN_M3a, and FAN_M3b.
• The board shall drive a K3 relay coil using a dedicated low-side MOSFET controlled by IO_B4.
• The board shall host two A4988 stepper driver modules for M4 and M5.
• The board shall generate a precision +5V_REF rail from +12V using REF195 for ADS1256 AVDD and sensor excitation.
• The board shall expose SPI to the ADS1256 harness and the SD module with independent chip selects.
• The board shall expose RTC access over the shared I2C bus.
• The board shall isolate three 24 V PELV feedback signals using PC817 optocouplers and present active-low 3.3 V logic outputs.

• Input power: +12V from J1, +3V3/+5V from J2.
• Key rails: +12V, +5V, +5V_REF, +3V3, GND, isolated PELV_GND.
• REF195 load current target is approximately 22 mA and shall remain below 30 mA.
• Optocoupler LED series resistance shall be 3.3 kΩ at 1/4 W, producing approximately 6.9 mA from 24 V.
• MOSFET gate resistors shall be 100 Ω for Q1-Q5 and 1 kΩ for Q6.
• MOSFET gate pull-down resistors shall be 10 kΩ.
• A4988 VMOT bulk capacitance shall be 100 µF per driver.
• REF195 input and output capacitance shall be 10 µF each.
• I2C pull-up pads should be provided only if not already present on A-MAIN.

• MOSFETs use TO-220 packages.
• Stepper drivers are socketed Pololu-style carrier modules.
• Maintain at least 2 mm creepage between PELV and 3.3 V domains.
• No copper pour under the optocoupler isolation barrier.
• Provide mounting clearance for M3 standoffs and at least 5 mm to cabinet housing.

• Star ground shall be established at J1.2.
• REF195 analog ground return shall go separately to the star point and avoid motor currents.
• Motor and +12V high-current paths require wider traces than logic/reference paths.
• The 24 V PELV input domain shall remain galvanically isolated from PCB logic ground.
• The board shall preserve unresolved TBD items in documentation without blocking schematic completion.
• Prefer surface-mount passives; connectors and power/mechanical parts may remain through-hole.

• A-MAIN board provides +3V3, +5V, I2C, SPI chip-select host logic, and IO_B4.
• ADS1256 and sensor chain consume +5V_REF and are external to this board.
• Motor and relay operating details depend on external harnesses and final system settings.

• Missing confirmation of SD_CS assignment, I2C pull-up ownership, and some optocoupler source semantics.
• M5 stepper current setpoint remains TBD pending motor data.
• Incorrect grounding around REF195 could degrade analog reference performance.

• Complete schematic includes all major functional blocks and connectors from TRIBO-ELEK-012.
• Nets represent the documented power, control, motor, and isolated interface connectivity.
• Open items remain clearly documented where the specification is incomplete.

• Schematic completeness review against the extracted block list and netlist.
• Review for missing decoupling, pull-downs, pull-ups, and connector wiring.
• Verify separated analog and isolated domains are preserved in schematic intent.

• Schematic
• BOM-ready component selection for all placeable parts available in the Flux library
• Documented open questions and assumptions

• I2C pull-up components should be included as optional placeholders unless A-MAIN ownership is confirmed.
• K3 flyback diode is intentionally omitted per specification due to avalanche-rated MOSFET assumption.
• ADS1256 reset and sync are assumed hardwired on the external module.

• Converted TRIBO-ELEK-012 into project-level requirements and architecture.
• Captured board interfaces, constraints, and unresolved TBD items for schematic execution.

• TBD-1: SD_CS GPIO number assignment at A-MAIN
• TBD-3: Final A4988 microstep setting for U2 and U3
• TBD-4: Final VREF/current target for M5 oil pump driver
• TBD-6: Whether A-MAIN already provides I2C pull-ups
• TBD-8: Whether Arctic P12 PWM pin 4 needs on-board handling
• TBD-9: Whether HW-111 SQW/INT is needed
• TBD-11: Confirm full REF195 output load budget
• TBD-15: Exact OC1 source definition
• TBD-16: Exact OC3 door-contact polarity