Chessboard pcb

Imperium

An Autonomous, Sensor-Driven Chessboard with Electromagnetic Piece Control

Abstract

Imperium is a fully autonomous chessboard that detects and moves pieces using a precision electromagnetic gantry, per-square Hall-effect sensing, and CNC-style motion control. The system integrates custom mechanical design, multi-PCB electronics, and firmware-level motion planning to deliver seamless, repeatable gameplay without manual calibration.

System Overview

flowchart LR
    Pieces[Chess Pieces — Magnets]
    Sensors[Hall Sensor Matrix — 64 Squares]
    Mux[16:1 Multiplexers]
    MCU[ESP32 Master Controller]
    Drivers[TMC2209 Motor Drivers]
    Motors[Stepper Motors — T-Bot Gantry]
    Magnet[Electromagnet]

    Pieces --> Sensors
    Sensors --> Mux
    Mux --> MCU
    MCU --> Drivers
    Drivers --> Motors
    MCU --> Magnet

Project Media

Completed System

Figure 2: Fully assembled Imperium chessboard

Videos

• 🎥 demonstration video
• 🎥 piece movement

Hardware Architecture

Mechanical Subsystem

CAD Figure: T-Bot gantry layout and belt routing

Gantry Design

• Type: T-Bot (CoreXY derivative)
• Motors: 2× NEMA 17
• Linear motion: 2× MGN12 rails (450 mm)
• Drive: GT2 belts & pulleys
• End effector: Electromagnet (custom mount)

Design Rationale

• Compact footprint compared to CoreXY
• Sufficient precision for chess (no micron-level requirement)
• Reduced part count and cost

Sensing Architecture

Hall Sensor Matrix

flowchart LR
    Square1[Square 1]
    Square2[Square 2]
    SquareN[Square 64]
    Mux1[16:1 MUX]
    MCU[ESP32]

    Square1 --> Mux1
    Square2 --> Mux1
    SquareN --> Mux1
    Mux1 --> MCU

Figure 5: 64-square Hall-effect sensor grid

• Sensors: KTH-1601 (46 Gs threshold)
• 1 sensor per square (64 total)
• Mounted beneath ~3 mm acrylic

Why Hall Sensors

• Instantaneous response
• No ghosting (unlike reed switches)
• Reliable removal detection

PCB Sheet Layout

flowchart TB
    PCB1[Hall PCB Sheet 1\n16 Sensors]
    PCB2[Hall PCB Sheet 2\n16 Sensors]
    PCB3[Hall PCB Sheet 3\n16 Sensors]
    PCB4[Hall PCB Sheet 4\n16 Sensors]
    Master[Master PCB]

    PCB1 --> Master
    PCB2 --> Master
    PCB3 --> Master
    PCB4 --> Master

Figure 6: Hall sensor PCB sheet (100 mm × 400 mm)

Each PCB sheet contains:

• 16 Hall sensors
• 1× 16:1 multiplexer
• Local decoupling capacitors
• Ribbon cable interface

Total sheets: 4

Control Electronics

Master Control Board

Figure 7: Master PCB functional block diagram

Core Components

• MCU: ESP32
• Motor drivers: 2× TMC2209 (UART)
• Power:
  • 12 V rail (motors + electromagnet)
  • Buck converter → 3.3 V logic
• Electromagnet switching via transistor

All schematics and footprints were custom-designed in KiCad.

UART Motor Control

Chess pieces are moved exclusively along square edges rather than diagonals. This design choice:

Prevents collisions with stationary pieces

Simplifies motion planning

Ensures consistent and predictable movement paths

The gantry executes all moves as a sequence of orthogonal segments.

UART enables:

• Sensorless homing
• Stall detection
• Current tuning
• Advanced diagnostics

Control Flow

1. Board State Detection
   Hall sensor matrix scans current piece positions.

2. Move Translation
   Chess moves converted into constrained paths.

3. G-Code Generation
   Custom G-code enforces non-diagonal movement.

4. Execution
   G-code executed by FluidNC on ESP32.

Bill of Materials (BOM)

📎 Full BOM:
https://docs.google.com/spreadsheets/d/1yp7t6AiXMwJCAfVlhCX7udocGjks9lOOFWkv4rPJByo/view

Results

• Reliable autonomous gameplay
• Accurate per-square detection
• Consistent homing and positioning
• No recalibration required between games

Future Work

• Chess engine integration
• Companion UI / mobile app
• Faster traversal paths
• Noise reduction
• Fully enclosed consumer-ready housing

References

• CoreXY reference — https://corexy.com
• Gantry design pitfalls — https://drmrehorst.blogspot.com