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Hardware

michess is built around a Raspberry Pi 4 reading a 64-antenna NFC matrix. This page covers the component list, the multiplexer topology, and the LED system.

Bill of Materials

Component Quantity Notes
Raspberry Pi 4 1 Main controller; 2 GB RAM minimum
PN532 NFC reader modules 8 One per 8-square group
CD74HC4067 16-channel multiplexers 4 For antenna switching
NFC tags (13.56 MHz, NTAG213) 32 Embedded in piece bases
Custom loop antennas 64 One per square, ~1–2 μH
WS2812B LEDs 64+ For move indication

See hardware/bom/ for a full bill of materials with UK suppliers and current pricing.

NFC Matrix Architecture

Why a matrix of antennas?

Standard NFC readers have a single antenna with a read range of ~4 cm. To cover all 64 squares without moving parts, michess uses 64 small loop antennas - one per square - switched via multiplexers so that a single PN532 module scans 8 squares in sequence.

Multiplexer topology

Raspberry Pi (I²C / SPI)
    │
    ├─ PN532 #1 ── MUX ── antennas a1–a8
    ├─ PN532 #2 ── MUX ── antennas b1–b8
    ├─ PN532 #3 ── MUX ── antennas c1–c8
    ├─ PN532 #4 ── MUX ── antennas d1–d8
    ├─ PN532 #5 ── MUX ── antennas e1–e8
    ├─ PN532 #6 ── MUX ── antennas f1–f8
    ├─ PN532 #7 ── MUX ── antennas g1–g8
    └─ PN532 #8 ── MUX ── antennas h1–h8

Each CD74HC4067 16-channel multiplexer connects one PN532 to 8 antenna coils in sequence (only 8 of the 16 channels are used per MUX). The Pi cycles through all 8 reader modules, reading 8 squares each, giving a full 64-square scan in under 2 seconds.

Antenna design

The loop antennas are custom-designed PCB coils tuned to 13.56 MHz. Each coil sits directly beneath a board square, routed through the multiplexer to its assigned PN532. See hardware/antenna-design/ for coil dimensions and tuning notes.

LED System

WS2812B addressable LEDs are placed beneath each square. The Raspberry Pi drives the LED strip directly over a single GPIO pin using the rpi_ws281x library. The LEDs indicate:

  • Engine move - highlight the from-square and to-square
  • Check - flash the king's square
  • Illegal move - brief red flash on the lifted piece's origin square

PCB Design

The project uses KiCad for PCB design. Source files are in hardware/pcb/. Gerber files are not committed - regenerate them from source when needed.

Enclosure

The enclosure is designed in FreeCAD (source in hardware/enclosure/). The top surface is a wood veneer panel with LEDs diffused through it. STL files are not committed - export from the FreeCAD source.

Licences

All hardware designs are released under CERN-OHL-S v2. You are free to manufacture, modify, and sell boards based on this design, but must share modifications under the same licence.