Week 11 Embedded Networking and Communications

This week, after learning I2C communication, I used my own PCB with a XIAO-ESP32-C3 (master) to communicate. It is connected to a computer to read serial input (keyboard 1 or 2) and control the LED connected to D7 on the Arduino (slave). I also used an Arduino UNO to create an RFID door lock system.

Learning Objectives

Group Assignment

• Send a message between two projects.

Individual Assignment

• design, build and connect wired or wireless node(s) with network or bus addresses and a local input and/or output devices.

Learning highlights

I2C communication(XIAO-ESP32-C3 & Arduino Uno)

An RFID Door Lock System

Group Assignment

1.1 Embedded Network and Communication

Refers to how these systems exchange information via wired or wireless networks to achieve collaboration and control.

1.2 Common Communication Methods

Type	Common Protocol	Features	Applicable Scenarios
Wired	UART	Simple, point-to-point	Direct communication between Arduino UNO, Xiao ESP32
	I2C	Supports multi-master/multi-slave, two-wire bus	Multiple sensors, multi-slave control
	SPI	High-speed, full duplex	Sensors, high-speed peripherals
Wireless	Wi-Fi	Long distance, Internet access	Smart home, remote monitoring
	Bluetooth/BLE	Low power, short distance	Mobile interaction, data synchronization
	LoRa	Ultra long distance, low speed	IoT, sensor networks
	Zigbee	Self-organizing, low power	Smart home, sensor networks

2.1 I2C Communication

I2C (Inter-Integrated Circuit) is a two-wire, synchronous, half-duplex, master-slave serial communication bus developed by Philips (now NXP).

2.2 I2C Physical Connection

Wire	Function
SDA (Serial Data)	Data line
SCL (Serial Clock)	Clock line

2.3 I2C Roles: Master and Slave

• Master: initiates communication, generates clock, sends commands.
• Slave: has a unique address, responds only when queried by master.

3.1 I2C Communication Test with Two Arduino Uno

Master board: connected to computer, reads serial input (keyboard A or B), sends it via I2C to the slave.

Slave board: receives I2C message and controls onboard LED (D13) accordingly.

3.2 Upload Code

Step 1: Upload Slave code

Step 2: Upload Master code

3.3 Hardware Connection

Master UNO	Slave UNO	Note
A4 (SDA)	A4 (SDA)	I2C data line
A5 (SCL)	A5 (SCL)	I2C clock line
GND	GND	Common ground
5V	5V	Power optional

3.4 Test

Press A on the keyboard → LED turns on;Press B on the keyboard → LED turns off.

video

Code01 for this week Code02 for this week

Individual Assignment

After learning I2C communication, I used my own PCB with a XIAO-ESP32-C3 (master) to communicate. It is connected to a computer to read serial input (keyboard 1 or 2) and control the LED connected to D7 on the Arduino (slave)

1.1 Upload Slave Code

LED connection

code

Serial output: I2C Slave Ready

1.2 Upload Master Code

code

The serial monitor shows: ESP-ROM: esp32c3-api1-20210207 I2C Master is ready. Press 1 to turn the LED ON, 2 to turn it OFF.

1.3 Hardware Connection

Signal	ESP32-C3	Arduino Uno
SDA	D6	SDA
SCL	D7	SCL
GND	GND	GND
LED	—	D7 → LED → GND

1.4 Test

Press 1 on the keyboard → LED turns on; Press 2 on the keyboard → LED turns off.

Video

Code03 for this week Code04 for this week

In an access control system, the RC522 module is used to detect RFID cards and read their UID. The node sends the UID to the master controller through a wired I2C connection. The master controller then parses the UID and instructs the display to record and show the information.

1 Introduction

1.1 RFID

RFID uses electromagnetic waves in the radio frequency spectrum for communication and data transfer. RFID tags are used in many industries and we can find them in product tags from stores to security access cards. RFID tags can expedite the checkout and can be used for antitheft measures.

Components of an RFID System An RFID system typically consists of several main components, each playing a different role in the system.

Component	Description
RFID Tag	Used to store and transmit information.
RFID Reader	Reads the data from the RFID tag by emitting radio waves. It communicates with a microcontroller or computer.
Antenna	Transmits and receives radio waves between the RFID tag and reader, influencing the system's range and performance.
Middleware	Software that manages and processes the data between the RFID system and application, facilitating communication with the database.
Software	Used to process and manage the data from RFID tags and integrate it into applications (e.g., security, inventory management).
Database	Stores the RFID tag information and related data, enabling real-time updates and retrieval of relevant data for processing.
Power Supply	Provides necessary power for the RFID system, especially for active tags and readers.

1.3 RC522 RFID

The RC522 RFID is a popular RFID reader/writer module that communicates with microcontrollers like Arduino. It uses the MFRC522 chip and supports reading and writing of 13.56 MHz RFID cards/tags.

RC522 RFID Module Pins and Descriptions

Pin	Description
SDA / SCL	I2C Communication pins: Data (SDA) and Clock (SCL).
SS / SCK / MOSI / MISO	SPI Communication pins: Slave Select (SS), Clock (SCK), Master Out Slave In (MOSI), and Master In Slave Out (MISO).
RX / TX	UART Communication pins for serial data transmission.
IRQ	Interrupt signal from the module to indicate RFID tag detection.
GND	Ground pin that needs to be connected to the GND pin on the Arduino.
RST	Reset pin for the module.
VCC	Supply pin for the module. The supply voltage ranges from 2.5V to 3.3V and must be connected to the 3.3V pin on the Arduino.

RC522 RFID Reader/Writer Module|Parts&Circuit Diagram

2 Circuit Setup

2.1 Components

RFID Module & Arduino Uno Board & RFID Key Tag & Relay Module & I2C LCD1602 & Breadboard & Jumper Wires

2.2 Circuit Setup

2.2.1 RFID Module

RFID Module	Arduino Uno
3.3V	3.3V
GND	GND
RST	2
SDA (SS)	10
MOSI	11
MISO	12
SCK	13
IRQ	7

2.2.2 I2C LCD1602

I2C LCD1602	Arduino Uno
GND	GND
VCC	5V
SDA	A4
SCL	A5

2.2.3 Relay Module

Relay Module	Arduino Uno
SIG	8
VCC	5V
GND	GND

3 Reading an RFID Tag

3.1 Installing the MFRC522 Library

1. Open Arduino IDE.
2. Click Tools → Manage Libraries (S+C+M)
3. In the search bar, type: MFRC522.
4. Find MFRC522 by GithubCommunity.
5. Click the Install button.

Notes:Place the RFID key tag near the center of the reader

3.2 Test Code

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 10
#define RST_PIN 2
MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
    Serial.begin(9600);
    SPI.begin();
    rfid.PCD_Init();
    Serial.println("Scan RFID Card...");
}

void loop() {
    if (!rfid.PICC_IsNewCardPresent()) {
        return;
    }
    if (!rfid.PICC_ReadCardSerial()) {
        return;
    }
    Serial.print("Card ID: ");
    for (byte i = 0; i < rfid.uid.size; i++) {
        Serial.print(rfid.uid.uidByte[i], HEX);
        Serial.print(" ");
    }
    Serial.println();
    rfid.PICC_HaltA();
}
    

3.3 Card ID

Serial Debugging: Viewing scanned card IDs in the Serial Monitor.

Card ID 1: 73 B2 63 D

Card ID 2: D3 E1 5C A3

RFID Serial Monitor Output & Troubleshooting

Serial Monitor Output	Possible Issue	Suggested Solution
⚠ ERROR: RFID module not detected	Wiring issue or incorrect power supply	ensure standard SPI pins and 3.3V power are used
No card detected	No RFID card detected near reader	Try a different RFID card, adjust scanning angle, or ensure the card is 13.56MHz.
Failed to read card	Read failure due to card or hardware issue	Try another card, adjust timing (add delay), or test another RFID module.
Card ID: xx xx xx xx	Success	RFID card read successfully. Use this ID for verification logic.

4 RFID Door Lock System Code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 10
#define RST_PIN 2
#define RELAY_PIN 8

MFRC522 rfid(SS_PIN, RST_PIN);
LiquidCrystal_I2C lcd(0x27, 16, 2);
byte allowedUID[4] = {0x73, 0xB2, 0x63, 0xD};

void setup() {
    Serial.begin(9600);
    SPI.begin();
    rfid.PCD_Init();
    lcd.init();
    lcd.backlight();
    pinMode(RELAY_PIN, OUTPUT);
    digitalWrite(RELAY_PIN, LOW);
    lcd.setCursor(0, 0);
    lcd.print("Welcome !");
}

void loop() {
    if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) {
        return;
    }
    bool isAuthorized = true;
    for (byte i = 0; i < rfid.uid.size; i++) {
        if (rfid.uid.uidByte[i] != allowedUID[i]) {
            isAuthorized = false;
        }
    }
    if (isAuthorized) {
        digitalWrite(RELAY_PIN, HIGH);
        lcd.setCursor(0, 1);
        lcd.print("Welcome home !");
        delay(2000);
        digitalWrite(RELAY_PIN, LOW);
    } else {
        lcd.setCursor(0, 1);
        lcd.print("Unknown Guy !");
        delay(2000);
    }
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Welcome !");
    rfid.PICC_HaltA();
}
    

5 Compilation & Testing

Run Steps

• Reading RFID Cards: Detecting nearby cards and retrieving their IDs.
• LCD Display: Showing card ID and access status on the LCD1602 screen.
• Relay Control: Unlocking the door if the RFID card matches.
• Serial Debugging C OPEN & CLOSE

Run Results

At the beginning, we can see "Welcome!" displayed on the I2C LCD1602.

Swipe Card 1, and the relay's normally open contact will activate. The LCD will display:

• "ID: 73 B2 63 D"
• "Welcome Home!"

After two seconds, it will return to displaying "Welcome!".

Swipe Card 2, and if the ID is incorrect, the relay's normally open contact will deactivate. The LCD will display:

• "ID: D3 E1 5C A3"
• "Unknown Guy!"

After two seconds, it will return to displaying "Welcome!".

video