Control electronics and PCB architecture
========================================

Purpose
-------

- Provide a clear separation between:

  - motion control
  - process supervision
  - sensing and data acquisition
  - safety
- Enable extensible, modular sensing and supervision
- Avoid tight coupling between motion execution and adaptive logic

ECU (master PCB)
----------------

- Acts as real-time supervisory controller
- Responsibilities:

  - sensor fusion
  - machine state estimation
  - process supervision decisions
- Interfaces:

  - CAN-FD:

    - communication with distributed sensor PCBs
  - RS-485:

    - communication with spindle servo drive
  - GPIO:

    - low-latency triggering of Duet macros
  - SPI or UART:

    - communication with Raspberry Pi
- Does not:

  - generate motion trajectories
  - directly drive axes
  - participate in safety chain

Distributed sensor PCBs
-----------------------

- Zonal architecture:

  - multiple PCBs placed near sensors
- Connected to ECU via CAN-FD
- Responsibilities:

  - sensor signal acquisition
  - local filtering
  - FFT and envelope extraction
  - threshold detection
- Communication behavior:

  - event-driven data transmission
  - periodic heartbeat messages
- Fault handling:

  - ECU detects missing heartbeats
  - missing data treated as sensor failure
- Debug and validation:

  - raw data access via USB or SPI

Communication architecture
--------------------------

- CAN-FD used for:

  - robust, deterministic sensor data exchange
- SPI / UART used for:

  - configuration
  - logging
  - visualization
- GPIO used for:

  - low-latency supervisory actions
  - feed and spindle-related macros

Raspberry Pi integration
------------------------

- Runs Duet services and web interface
- Hosts plugins for:

  - configuration of ECU and sensor PCBs
  - data logging
  - visualization (e.g. Grafana)
- Not used for:

  - real-time control
  - safety-critical functions


Sensor PCB Capabilities
=======================

General Architecture
--------------------

Two identical distributed sensor PCBs are used.

- Mounted close to structural measurement locations.
- Based on an STM32G4 (CAN-FD capable).
- CAN-FD communication to the main ECU.
- Optional synchronization line for deterministic simultaneous sampling.
- Careful separation of analog and digital domains.

All nodes share the same CAN-FD bus. The ECU is located at one physical
end of the bus.


CAN Topology Overview
---------------------

.. mermaid::

  flowchart LR
  %% --- CAN participants forced horizontal ---
  subgraph CAN_BUS
    direction LR

    ECU["ECU
    Main Controller
    CAN-FD"]

    SN_A["Sensor Node A
    Left X-Beam"]

    SN_B["Sensor Node B
    Right X-Beam"]

    ECU ---|CAN-FD Bus| SN_A ---|CAN-FD Bus| SN_B
  end


  %% --- Node B sensors (ABOVE SN_B) ---
  DMS_R["X-Beam DMS - Right
  Beam bending
  Dynamic load estimation"]

  ACC_T["Tower Accelerometer
  Structural vibration"]

  MIC_T["Tower Microphone
  Structural acoustics"]

  TEMP_T["Tower Temperature
  Structural temperature"]

  DMS_R --> SN_B
  ACC_T --> SN_B
  MIC_T --> SN_B
  TEMP_T --> SN_B


  %% --- Node A sensors (BELOW SN_A) ---
  DMS_L["X-Beam DMS - Left
  Beam bending
  Dynamic load estimation"]

  ACC_SP["Spindle Plate Accelerometer
  Vibration + Low-freq tilt"]

  MIC_SP["Spindle Housing Microphone
  Bearing and chatter acoustics"]

  TEMP_SP["Spindle Housing Temperature
  Thermal growth monitoring"]

  DMS_L --> SN_A
  ACC_SP --> SN_A 
  MIC_SP --> SN_A 
  TEMP_SP -->SN_A


Strain Gauge Interface
----------------------

- Supports multiple full-bridge configurations.
- External 24-bit ADC recommended for dynamic strain measurement.
- Differential low-noise instrumentation front-end.
- Bridge excitation provided by PCB.
- Shielded differential wiring to remote DMS.

Typical usage:

- 2 × X-beam full bridges.


Accelerometer Interface
-----------------------

- SPI interface for digital 3-axis accelerometers.
- Deterministic sampling capability.
- Remote mounting via short shielded cable or rigid daughterboard.
- Optional synchronization between PCBs.

Typical usage:

- 1 × spindle plate accelerometer.
- 1 × tower accelerometer.


Microphone Interface (Piezo Surface Microphone)
-----------------------------------------------

- High-impedance charge amplifier front-end.
- Anti-alias filtering.
- Analog input to ADC.
- Shielded cable required.

Typical usage:

- 1 × spindle housing microphone.
- 1 × tower microphone.


Temperature Sensor Interface
----------------------------

- SPI/I²C thermocouple frontend or RTD interface.
- Alternatively precision analog temperature input.
- Slow sampling rate sufficient.

Typical usage:

- 1 × spindle housing temperature.
- 1 × tower plate temperature.


Piezo Shunt Communication Interface
-----------------------------------

- SPI or I²C master interface.
- Used to communicate with external piezo shunt PCBs.
- No high-voltage circuitry on the sensor PCB.
- Digital control and monitoring only.