🔍 CoinTrace™

Open-source coin metal analyzer using inductive sensing Identifies metal alloy composition via attenuation curve fingerprinting

Author: Yuriy Kachmaryk | Location: Lviv, Ukraine | First published: 2026-03-08

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📖 Table of Contents

• What is CoinTrace™?
• How It Works
• vs Competitors
• Hardware
• Wiring
• Getting Started
• Supported Metals
• Fingerprint Database
• Project Roadmap
• Prior Art
• Contributing
• License

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⚡ What is CoinTrace™?

CoinTrace™ measures the attenuation curve of a coin's electromagnetic response across 4 controlled distances using an LDC1101 inductive sensor. This creates a unique "fingerprint" that identifies the coin's metal composition — without touching, scratching or damaging the coin.

Why CoinTrace™?

	Commercial verifiers (~$250–600)	CoinTrace™ (~$40)
Method	Single resistivity value	Attenuation curve (4 points)
Frequency sweep	Fixed or single frequency	Single frequency (extensible)
Database	Closed, proprietary	Open community database
Coin identification	Metal type only	Specific coin fingerprint
Source code	Closed	GPL v3 open source
Price	$250–600	~$40 components

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🧬 How It Works

CoinTrace™ takes 4 measurements at different distances and builds an attenuation curve unique to each metal:

Step 1: Baseline (no coin)     → Rp₀, L₀
Step 2: Coin at 0mm (direct)   → Rp₁, L₁
Step 3: Coin + 1mm spacer      → Rp₂, L₂
Step 4: Coin + 3mm spacer      → Rp₃, L₃

Size-independent normalization (key innovation):

ΔRp₁ = Rp₁ - Rp₀   (absolute change)
ΔRp₂ = Rp₂ - Rp₀
ΔRp₃ = Rp₃ - Rp₀

k1 = ΔRp₂ / ΔRp₁   ← independent of coin size!
k2 = ΔRp₃ / ΔRp₁   ← independent of coin size!

Fingerprint vector:

F = [ΔRp₁, k1, k2, slope, ΔL₁]

Identification via Euclidean distance to known fingerprints:

dist = √((ΔRp₁ - ref_ΔRp₁)² + (k1 - ref_k1)² + (k2 - ref_k2)²)
confidence = 1 - (dist / max_dist)

Physics — Skin Effect

Different metals have different conductivity → different skin depth:

Metal	Conductivity	Skin depth @ 1MHz	Curve shape
Silver 999	63 MS/m	~67 µm	Steepest
Copper	59 MS/m	~69 µm	Very steep
Gold 999	45 MS/m	~80 µm	Medium
Aluminum	37 MS/m	~88 µm	Medium
Steel	6–10 MS/m	~200 µm	Flattest

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🔧 Hardware

Bill of Materials

Component	Model	~Price
Main controller	M5Stack Cardputer-Adv (ESP32-S3)	~$30
Inductive sensor	LDC1101 Click Board (MIKROE-3240)	~$27
Spacers (1mm, 3mm)	3D printed or cardboard	free
Total		~$57

Features of Cardputer-Adv

• ESP32-S3FN8 @ 240 MHz dual-core
• 1.14" TFT color display (240×135)
• 56-key keyboard
• 1750 mAh built-in battery
• microSD card slot (fingerprint database storage)
• WiFi + BLE 5.0
• BMI270 IMU (detects level positioning)
• USB-C (Serial + OTA updates)

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🔌 Wiring

LDC1101 Click Board → Cardputer-Adv EXT Header

LDC1101 Click    EXT Header Pin    GPIO
─────────────────────────────────────────
SCK          →   Pin 7          → G40
MOSI         →   Pin 9          → G14
MISO         →   Pin 11         → G39
CS           →   Pin 13         → G5
INT (INTB)   →   Pin 3          → G4
GND          →   Pin 4          → GND
3.3V         →   Stamp-S3A 3V3  → 3V3

⚠️ Note: G40/G14/G39 are shared with microSD SPI bus. Use separate CS pins. Managed automatically in firmware.

EXT Header Pinout Reference

┌─────────────────────────────┐
│  1 (G3/RST)  ○  ○  2 (5VIN)│
│  3 (G4/INT)  ●  ○  4 (GND) │  ← LDC INT + GND
│  5 (G6)      ○  ○  6 (5VOUT│
│  7 (G40/SCK) ●  ○  8 (G8)  │  ← LDC SCK
│  9 (G14/MOSI)●  ○  10(G9)  │  ← LDC MOSI
│  11(G39/MISO)●  ○  12(G13) │  ← LDC MISO
│  13(G5/CS)   ●  ○  14(G15) │  ← LDC CS
└─────────────────────────────┘

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🚀 Getting Started

For Developers (Modify Firmware)

Want to customize CoinTrace firmware or contribute code?

📖 Development Setup Guide — Complete guide for setting up VS Code + PlatformIO on Windows. Covers:

• Install development tools (VS Code, PlatformIO, drivers)
• Clone and build CoinTrace firmware
• Upload to M5Stack Cardputer-Adv
• Understand project structure and M5Stack API
• Troubleshooting and debugging

Beginner-friendly: Never coded before? The guide walks you through everything step-by-step.

⚠️ CoinTrace replaces the factory firmware and flash partition layout. Restoring to stock M5Stack firmware is always possible and takes ~5 minutes using M5Burner (free, no command line needed). Full restore instructions: STORAGE_ARCHITECTURE.md §18

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Quick Start (Advanced Users)

Already have PlatformIO? Quick setup:

Prerequisites

• PlatformIO already installed
• M5Stack Cardputer-Adv board
• LDC1101 Click Board (MIKROE-3240)
• 7 jumper wires
• USB-C cable (data + power)

Installation

# Clone repository
git clone https://github.com/xkachya/CoinTrace.git
cd CoinTrace/firmware

# Build and upload (PlatformIO)
pio run --target upload

# Monitor serial output
pio device monitor --baud 115200

PlatformIO Configuration

[env:cointrace-dev]
platform = espressif32@6.7.0
board = m5cardputer-adv         ; Custom board JSON in boards/m5cardputer-adv.json
framework = arduino
upload_speed = 921600
build_flags =
    -DESP32S3
    -DARDUINO_USB_CDC_ON_BOOT=1
    -DARDUINO_USB_MODE=1
    -DCOINTRACE_VERSION=\"1.0.0-dev\"
lib_deps =
    m5stack/M5Cardputer @ ^1.0.0
    Wire

Python Monitor (for data analysis)

cd tools/
pip install -r requirements.txt
python serial_monitor.py --port COM3 --baud 115200

Outputs real-time CSV + live attenuation curve plot.

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📊 Supported Metals

Currently in fingerprint database (Wave 8, 2026)

These 8 metal classes are implemented in the current firmware DB (FingerprintCache):

Metal	DB code	Conductivity	Notes
Silver 999	XAG999	63 MS/m	Steepest attenuation curve
Silver 925	XAG925	~60 MS/m	Sterling silver
Silver 833	XAG833	~53 MS/m	European 13-lot silver
Copper	XCU	59 MS/m
Nickel silver (zinc alloy)	XZNNIP	~4 MS/m	Cu-Zn-Ni alloy; close to XCU in 5D space
Nickel	XNI	14 MS/m
Aluminum	XAL	37 MS/m
Steel (ferromagnetic)	XFE	6–10 MS/m	Detected via ΔL axis; requires CLKIN HW

Planned for future waves

Metal	Conductivity	Notes
Gold 999	45 MS/m	Wave 9+ — requires calibrated samples
Gold 585	~27 MS/m	Wave 9+
Silver 900	~57 MS/m	Wave 9+

Note: Gold is intentionally excluded from the current DB — it is physically similar to Silver 925 in RP space and requires high-quality reference samples to distinguish reliably. It will be added after S-5 (ferro-detection) and S-6 (Gold separation) research tasks.

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🗄️ Fingerprint Database

CoinTrace™ uses a tiered fingerprint database:

🆓 Community tier (free, open source): Common metals and popular coins. Schema + basic dataset published under CC BY-SA 4.0. Works fully offline.

💎 Premium tier (subscription, future): Extended database of 5000+ coins via cloud API. The service is commercial — the protocol stays open. GPL v3 requires open code, not free services.

Each fingerprint is a normalized measurement vector that is device-independent — k1 and k2 values are the same across all CoinTrace™ devices.

Fingerprint Format

{
  "version": 1,
  "coin": {
    "name": "Austrian Maria Theresa Thaler",
    "year": 1780,
    "country": "Austria",
    "denomination": "1 Thaler",
    "diameter_mm": 39.5,
    "weight_g": 28.06,
    "metal": "Silver 833"
  },
  "fingerprint": {
    "dRp1": 312.4,
    "k1": 0.714,
    "k2": 0.388,
    "slope": -89.2,
    "dL1": 724.1
  },
  "metadata": {
    "device": "CoinTrace™ v1.0",
    "temp_c": 23.4,
    "date": "2026-03-21",
    "contributor": "ykachmaryk"
  }
}

How to Contribute a Fingerprint

1. Measure your coin with CoinTrace™
2. Export via keyboard: SAVE → EXPORT
3. Copy JSON from microSD
4. Submit via Pull Request to database/samples/

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🗺️ Project Roadmap

V1 — Basic Prototype (current)
  ✅ LDC1101 + Cardputer-Adv
  ✅ 4-distance measurement
  ✅ Logger system (Serial + RingBuffer, 40 unit tests)
  ✅ Serial data output
  ⬜ Python analysis tools
  ⬜ OLED/TFT display UI
  ⬜ Local fingerprint database (microSD)

V2 — CoinTrace™ Device
  ⬜ Full keyboard UI
  ⬜ WiFi sync with cloud database
  ⬜ OTA firmware updates
  ⬜ Temperature compensation (NTC)
  ⬜ 50+ coin fingerprints

V3 — Community Platform
  ⬜ Web API for fingerprint database
  ⬜ Free tier: common coins (open dataset, CC BY-SA)
  ⬜ Premium tier: 5000+ coins (subscription service)
  ⬜ Community contribution system
  ⬜ Mobile companion app

Future Research
  ⬜ Advanced measurement techniques
  ⬜ Enhanced classification algorithms
  ⬜ Additional sensor capabilities

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🛡️ Prior Art Disclosure

First published: 2026-03-08 Repository: https://github.com/xkachya/CoinTrace

This repository serves as a formal prior art disclosure for the following novel concepts:

1. Attenuation curve method — measuring LDC1101 Rp parameter at 4 controlled distances to build a distance-attenuation curve
2. Size-independent coefficients k1, k2 — normalized ratios enabling cross-device comparison without recalibration
3. Fingerprint vector [ΔRp₁, k1, k2, slope, ΔL₁] — unique identifier compared via Euclidean distance metric
4. Community fingerprint database — crowd-sourced normalized vectors for coin identification across multiple devices

Full disclosure: docs/concept/prior_art_disclosure.md

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🤝 Contributing

Contributions are welcome! See CONTRIBUTING.md.

Ways to Help

• 🔬 Add coin fingerprints — most valuable contribution!
• 🐛 Report bugs — open an issue
• 💡 Suggest features — open an issue with [FEATURE]
• 🔧 Submit code — fork → branch → PR
• ⭐ Star the repo — helps others find CoinTrace™

DCO — Developer Certificate of Origin

By contributing you certify you have the right to submit under GPL v3. Sign your commits: git commit -s

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📄 License

Component	License
Firmware (code)	GNU GPL v3.0
Hardware (schematics)	CERN OHL v2
Documentation	CC BY-SA 4.0

Copyright © 2026 Yuriy Kachmaryk, Lviv, Ukraine

Trademark Notice

CoinTrace™ is a trademark of Yuriy Kachmaryk. The software, hardware designs, and documentation are open source under GPL v3 / CERN OHL v2 / CC BY-SA 4.0 licenses, but the CoinTrace™ name and brand are protected. See LICENSE-BRAND.md for usage guidelines.

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🔗 Links

• 📁 Repository: https://github.com/xkachya/CoinTrace
• 🐛 Issues: https://github.com/xkachya/CoinTrace/issues
• 💬 Discussions: https://github.com/xkachya/CoinTrace/discussions
• 📋 Prior Art: https://github.com/xkachya/CoinTrace/blob/main/docs/concept/prior_art_disclosure.md

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CoinTrace™ is an independent open-source project not affiliated with any commercial coin verification company or MikroElektronika. CoinTrace™ is a trademark of Yuriy Kachmaryk. LDC1101 is a trademark of Texas Instruments. All product comparisons are based on publicly available specifications.