11. Networking and Communications

Hero Shot!

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Group Assignment

You can find more details on our lab site: TechWorks - Networking and Communications

Learning Outcomes:

• Understand the differences between communication protocols: UART, I²C, SPI
• Apply these protocols in real embedded systems
• Evaluate their pros and cons based on project requirements

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Overview of Communication Protocols

UART

• Universal Asynchronous Receiver-Transmitter
• Uses two wires (TX and RX)
• No clock signal — devices must agree on the baud rate
• Used for simple serial communication between two devices

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I²C

• Inter-Integrated Circuit
• Uses two lines: SDA (data) and SCL (clock)
• Allows multiple slave devices with unique addresses
• Slower but requires fewer pins and supports multi-master

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SPI

• Serial Peripheral Interface
• Uses four lines: MOSI, MISO, SCK, SS (chip select)
• Faster communication than I²C
• Ideal for high-speed sensors and displays but uses more GPIOs

🔄 Comparison of Communication Protocols: UART vs I²C vs SPI

Feature	UART	I²C	SPI
Wires Required	2 (TX, RX)	2 (SDA, SCL)	4 (MOSI, MISO, SCK, SS)
Speed	Up to 1 Mbps (standard); varies by implementation	Up to ~3.4 MHz (Fast Mode Plus / High Speed Mode)	Typically 10–50+ MHz
Complexity	Simple, point-to-point	Moderate; needs addressing, start/stop conditions, ACK/NACK handling	Higher; more pins, but straightforward full-duplex communication
Device Support	1:1 communication	Supports multiple devices via unique addresses on shared bus	Supports multiple devices using separate SS lines
Data Direction	Bi-directional (half/full-duplex)	Bi-directional on SDA	Full-duplex with separate MOSI and MISO lines
Clock Signal	No (asynchronous)	Yes (SCL line)	Yes (SCK line)
Master-Slave	Not strictly defined	Yes (1 master, multiple slaves)	Yes (1 master, multiple slaves)
Power Consumption	Low	Lower at idle; open-drain lines with pull-up resistors	Higher at high speed, but more power-efficient during fast data transfers
Pin Efficiency	High	Very high—only 2 pins for many devices	Lower—requires more pins, especially with multiple slaves
Range	Short to medium (typically under 15 meters)	Short (usually under 1 meter)	Very short (under 1 meter)
Error Checking	Optional parity bit	Built-in ACK/NACK mechanism	None inherently; must be implemented in software
Use Case Suitability	Serial communication between two devices (e.g., PC ↔ microcontroller)	Great for low-speed sensors, RTCs, EEPROMs, small OLEDs	Best for high-speed peripherals like displays, ADCs, SD cards
Multi-master Support	No	Yes (but rarely used)	No

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💡 Summary: - UART: Great for simple two-device serial communication. - I²C: Best when you want to connect many devices with minimal wiring. - SPI: Preferred for high-speed and high-performance communication, especially for displays and storage devices.

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UART Communication Protocol

XIAO RP2040 —> Arduino Uno

I started by connecting the Arduino Uno R3 and the XIAO RP2040. Since the Arduino works at 5V and the XIAO at 3.3V, I needed a voltage divider circuit to avoid damaging the XIAO.

Voltage Divider Circuit

Designed in Altium Designer:

1. Install: 1x3 header footprint from JLCPCB.
2. Calculate resistor values R1 “”1k”” and R2 “1k+1k” to divide 5V into 3.3V.
3. Simulate and fabricate using MODS as done in Electronics Production Week

Images:

Testing the voltage divider using a multimeter:

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Wiring: Arduino Uno —> XIAO RP2040

UART Code:

Arduino_Transmitter_UART

#include <SoftwareSerial.h> //to create another serial port on different pins.
SoftwareSerial ArduinoSerial(10, 11); // RX, TX

void setup() {
  Serial.begin(9600);
  ArduinoSerial.begin(9600);
  Serial.println("Arduino ready");

}

void loop() {
  ArduinoSerial.println("Hello from Arduino!");
  delay(1000);
}

XIAO_Reciver_UART

void setup() {
  // Start serial communication on both Serial (for debug) and Serial1 (for UART)
  Serial.begin(9600);   // Serial monitor
  Serial1.begin(9600);  // UART communication with Arduino Uno
}

void loop() {
  // Check if data is available on Serial1 (connected to Arduino)
  if (Serial1.available()) {
    // Read data from Serial1 and send it to Serial monitor
    String data = Serial1.readString();
    Serial.println("Received: " + data);
  }
}

Communication Test:

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I²C Communication Protocol

OLED Display with Arduino Uno “For Testing”

Wiring:

• VCC → 5V
• GND → GND
• SDA → A4
• SCL → A5

Code:

Used Adafruit_SSD1306 and Adafruit_GFX libraries to initialize and print to the OLED. I used the ssd1306_128x64_i2c example provided in the Arduino IDE.

1. Install Libraries:

2. Open the Library Manager and install:

   • Adafruit SSD1306
   • Adafruit GFX

3. Open Example:

4. Navigate to:
   File > Examples > Adafruit SSD1306 > ssd1306_128x64_i2c

   

5. Set Board:

6. Select board: Arduino Uno

7. Choose the correct COM port

8. Upload and Run

OLED Address Check

#include <Wire.h>

void setup() {
  Wire.setSDA(6); // GPIO6 = D4
Wire.setSCL(7); // GPIO7 = D5
Wire.begin();

  Serial.begin(9600);
  while (!Serial); // Wait for serial to be ready
  Serial.println("\nI2C Scanner");
}

void loop() {
  byte error, address;
  int nDevices = 0;

  Serial.println("Scanning...");

  for (address = 1; address < 127; address++) {
    Wire.beginTransmission(address);
    error = Wire.endTransmission();

    if (error == 0) {
      Serial.print("I2C device found at address 0x");
      if (address < 16) Serial.print("0");
      Serial.print(address, HEX);
      Serial.println("  !");

      nDevices++;
    }
    delay(5);
  }

  if (nDevices == 0)
    Serial.println("No I2C devices found\n");
  else
    Serial.println("done\n");

  delay(2000);
}

SSd1306 OLED Check

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

void setup() {
  Serial.begin(9600);
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    while (1);
  }

  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 10);
  display.println(F("SSD1306 Test"));
  display.display();
}

void loop() {}

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XIAO RP2040 —> OLED Display

This section explains how to connect an SSD1306-based OLED display to the XIAO RP2040 using the I²C communication protocol.

Wiring:

Ensure your OLED display operates at 3.3V (to match the XIAO RP2040’s logic level).

OLED Pin	XIAO RP2040 Pin
VCC	3V3
GND	GND
SDA	D4
SCL	D5

💡 Note: On the XIAO RP2040, the default I²C pins are: - SDA → D4
- SCL → D5

Code:

Included OLED initialization, I²C address setup, and message display.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET    -1  // No reset pin
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  Wire.setSDA(4);  // SDA on D4
  Wire.setSCL(5);  // SCL on D5
  Wire.begin();

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;); // Infinite loop if display not found
  }

  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 10);
  display.println(F("Hello XIAO!"));
  display.display();
}

void loop() {}

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Conclusion

Understanding the communication protocols UART, I²C, and SPI is essential for embedded systems. Choosing between I²C and SPI depends on your speed, wiring, and complexity requirements. For displays, I²C is simple and effective for basic OLEDs, while SPI is better for high-performance displays requiring fast data throughput.

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Files

Electronics

• Schematic + PCB voltage divider

• LIB_header1X3

• Voltage Divider Traces

• Voltage Divider Outline

Codes

• Arduino_Transmitter_UART

• XIAO_Reciver_UART

• SSd1306 OLED Check Code

• OLED I²C address Check Code

• ssd1306_128x64_I²C

• OLED_XIAO_I²C