Project Architecture Overview

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Overview

This section introduces the Asset Tracking project, which uses RFID technology combined with an ESP32 microcontroller to create a check-in/check-out system for personnel and asset management. Learning this section will enable you to:

Understand the overall architecture of the RFID-based tracking system
Identify the key hardware and software components involved
Describe the data flow from RFID scan to database recording
Recognize the buyer scenarios this project addresses on Alibaba.com

Prerequisites

Before starting this section, ensure you are familiar with:

Basic ESP32 capabilities (see Chapter 01)
MQTT protocol fundamentals (see Chapter 06)
Node-RED basic concepts (see Chapter 09)
Docker container basics (see Chapter 07)

Alibaba.com Buyer Scenario

Target Buyer

International buyers on Alibaba.com who need:

Factory attendance tracking: Record employee check-in/check-out times
Tool and asset management: Track借用/归还 of equipment, tools, or assets
Inventory entry/exit recording: Log items entering or leaving a warehouse
Work order tracking: Associate worker time with specific production orders

Buyer Pain Points

Pain Point	How This Solution Addresses
Manual time tracking is error-prone	RFID scan provides automated, accurate recording
Paper-based records are hard to analyze	Digital records enable reporting and analytics
Tool loss due to poor tracking	Each scan logs who has which asset and when
Difficult to calculate labor costs	Time entries are automatically linked to projects

System Architecture

High-Level Overview

┌─────────────────────────────────────────────────────────┐
│                    Asset Tracking System                   │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  [RFID Tags] ──→ [RC522 Reader] ──→ [ESP32]             │
│       ↑                                    │             │
│       │                                    │ MQTT/HTTP    │
│       │                                    ↓             │
│       │                              [WiFi Network]      │
│       │                                    │             │
│       │                                    │             │
│  ┌────┴────────────────────────────────────┴──────┐      │
│  │              Server Stack (Docker)               │      │
│  │  ┌──────────┐  ┌──────────┐  ┌──────────────┐  │      │
│  │  │ TimeTagger│  │ Node-RED │  │  Database    │  │      │
│  │  │ (REST API)│←─│ (Flow)   │←─│ (JSON File)  │  │      │
│  │  └──────────┘  └──────────┘  └──────────────┘  │      │
│  └────────────────────────────────────────────────┘      │
└─────────────────────────────────────────────────────────┘

Component Breakdown

Component	Role	Technical Notes
RFID Tags	Unique identifiers for personnel/assets	Passive tags, 13.56MHz (HF), no battery needed
RC522 Reader	Reads RFID tag UID	SPI interface, 3.3V only, ~3-5cm read range
ESP32	Main controller	WiFi + MQTT, reads tag, controls LEDs
TimeTagger	Time tracking software	Open source, REST API, Docker container
Node-RED	Flow automation	Orchestrates MQTT/HTTP communication
File-based storage	Local check-in state	JSON flat file on server

Data Flow

Check-In Flow

1. User taps RFID tag on reader
2. ESP32 reads tag UID via RC522 (SPI)
3. ESP32 publishes UID to MQTT topic
4. Node-RED receives MQTT message
5. Node-RED checks if check-in file exists on server
6. If file does NOT exist → This is a CHECK-IN
7. Node-RED creates JSON file with start timestamp
8. ESP32 turns on GREEN LED to indicate success

Check-Out Flow

1. Same user taps RFID tag again
2. ESP32 reads same UID via RC522
3. ESP32 publishes UID to MQTT topic
4. Node-RED receives MQTT message
5. Node-RED checks if check-in file exists
6. If file EXISTS → This is a CHECK-OUT
7. Node-RED reads the file, adds end timestamp
8. Node-RED sends complete record to TimeTagger API via HTTP POST
9. Node-RED deletes the local file
10. ESP32 turns on RED LED to indicate completion

State Machine

                ┌──────────┐
                │  IDLE    │
                │ (Waiting)│
                └────┬─────┘
                     │
              ┌──────▼──────┐
              │ Tag Detected │
              └──────┬──────┘
                     │
              ┌──────▼──────┐
         NO   │ File Exists?│   YES
     ┌────────┤   on Server ├────────┐
     │        └─────────────┘        │
     ▼                               ▼
┌──────────┐                  ┌──────────┐
│ CHECK-IN │                  │ CHECK-OUT│
│ Create   │                  │ Read File│
│ JSON File│                  │ POST API │
└────┬─────┘                  │ Delete   │
     │                       │ File     │
     │                       └────┬─────┘
     │                            │
     └──────────┬─────────────────┘
                ▼
          ┌──────────┐
          │  DONE    │
          │ (LED FB) │
          └──────────┘

Key Technical Decisions

Decision	Choice	Rationale
RFID Frequency	13.56 MHz (HF)	Good balance of read range and tag cost; works for proximity tracking
Reader Module	RC522	Widely available, low cost (~$2), Arduino library support
Data Storage	Flat file on server	Simple, no database dependency; TimeTagger as final record
Server Communication	MQTT + HTTP	MQTT for real-time events; HTTP REST for TimeTagger API
State Persistence	JSON file Node-RED	Survives server restarts; easy to inspect and debug

Project Sections Overview

This chapter is organized into the following sections:

Section	Topic	Focus
05-02	RFID Reader Hardware Setup	Wiring the RC522 module to ESP32
05-03	RC522 Module Integration	Library setup and SPI configuration
05-04	RFID Tag UID Reading	Reading and validating tag identifiers
05-05	TimeTagger Open Source Software	Installing and configuring TimeTagger
05-06	REST API Authentication	Obtaining and using API tokens
05-07	HTTP POST Request Implementation	Building and sending POST requests
05-08	Check-In API Integration	Full check-in/check-out flow
05-09	State Management Logic	File-based state tracking
05-10	LED Status Indicators	Visual feedback for operations
05-11	Technical Capability Assessment	Evaluating solution boundaries
05-12	Customization Possibilities	Adapting to different buyer needs

Verification

After completing this chapter, you should be able to:

Explain the complete check-in/check-out flow to a buyer
Identify the role of each component in the architecture
Describe how RFID-based tracking solves factory attendance requirements
Understand the difference between check-in and check-out state management

Summary

Key takeaways:

System architecture: RFID tags → RC522 → ESP32 → MQTT → Node-RED → TimeTagger
Two-phase flow: Check-in (create file) and Check-out (send to API + delete file)
State management: File existence on server determines check-in vs check-out behavior
Buyer alignment: Solves factory attendance, tool tracking, and asset management needs

References

Writing Date: 2026-05-17
Based on Source File: 校正版/10 Time recording witht RFID und TimeTagger.md
Target Audience: Alibaba.com IoT Pre-sales Engineer
Status: ✅ Completed

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