Expanders

HomeBus Base Node

The HomeBus Base Node is the primary in-wall actuator and sensor module in the HomeBus distributed automation network. Designed to fit into standard residential switch flush boxes behind wall plates, it interfaces physical toggle switches and rotary encoders with the HomeBus RS-422 serial bus while driving external relay modules to switch lights, appliances, and inductive loads.

Visual Previews

3D Production Renders

Front View (Component Side)	Back View (Connector Side)

Manufacturing Schematic

Hardware Architecture

flowchart LR
    subgraph Power ["Power Subsystem"]
        BUS_IN["24V DC Bus Rail"] --> BUCK["MP1584EN Buck Converter\n(24V -> 5V DC @ 3A)"]
        BUCK --> VDD["5V Logic Rail"]
    end

    subgraph BusInterface ["RS-422 Interface"]
        RS422["XY2500 6-Pin Bus Header\n(24V, GND, TX±, RX±)"]
        TVS["SM712 TVS Array\n(-7V to +12V Protection)"]
        XCVR["MAX491 Transceiver\n(Full-Duplex RS-422)"]
        RS422 <--> TVS <--> XCVR
    end

    subgraph Processing ["Core MCU"]
        MCU["WCH CH32X033F8P6\n(32-bit QingKe RISC-V @ 48 MHz)"]
    end

    subgraph Inputs ["Input Subsystem"]
        DIP["8-Bit DIP Switch\n(Hardware Node ID)"]
        WALL["External Wall Switches /\nRotary Encoders (JST-PH)"]
        SR["74HC165D Shift Register\n(8-bit PISO Shift Register)"]
        DIP --> SR
        WALL --> SR
    end

Key Hardware Components

Pin Allocation Table

The Base Node assigns the 20 pins of the CH32X033F8P6 as follows, differentiating between Development mode (SWD debug available) and Production mode (SWD pins repurposed for actuator GPIOs):

Revision History

1. base_node (v1.0): Initial prototype layout. Used orthogonal 45° routing and tested basic connectivity between the CH32X033 and MAX491.
2. base_node-rounded (v1.1): Experimental PCB layout with circular/curved track fillets using KiCad round-tracks plugin for aesthetic evaluation and high-speed trace continuity.
3. base_node_clad (v1.2): Added continuous solid copper pour cladding across top and bottom layers, significantly reducing ground impedance and improving EMI containment in high-noise AC environments.
4. base_node_clad_v2 (v2.0 - Production):
   • Optimized high-voltage isolation creepage and clearance distances between mains-connected lines and low-voltage logic.
   • Refined component clearances for compact hand-soldering and reflow stenciling.
   • Added reinforced thermal pads and teardrop transitions on signal vias.
   • Verified Gerber generation ready for industrial fabrication under Basenode_gerber/.

Manufacturing & Assembly

• Gerber Files: Ready-to-manufacture archives are stored in Basenode_gerber/base_node.zip.
• PCB Fabrication Parameters:
  • Layers: 2-layer FR-4
  • Board Thickness: 1.6 mm
  • Copper Weight: 1 oz (35 µm)
  • Surface Finish: HASL Lead-Free / ENIG recommended
  • Minimum Trace / Space: 0.2 mm / 0.2 mm
  • Solder Mask: Blue / Matte Black
  • Silkscreen: White
• Fabrication Plots:
  • Top Copper: base_node_clad_v2-F_Cu.pdf
  • Bottom Copper: base_node_clad_v2-B_Cu.pdf
  • Edge Cuts / Outline: base_node_clad_v2-Edge_Cuts.pdf

Navigation

• ← Hardware Subsystem Overview
• ↑ HomeBus Root Documentation
• Gateway Node Documentation →
• Fan Controller Node Documentation →
• Expander Daughterboards Documentation →
• Firmware & Protocol Specification →