Message Transmission Demonstration

• Setup: Assembled two XIAO-RP2040 boards on a breadboard, connected via UART (wired communication). Node 1 acts as the sender, and Node 2 as the receiver.
  • Wiring: Node 1 TX (D6) to Node 2 RX (D7), Node 1 RX (D7) to Node 2 TX (D6), common GND between both boards.
  • Node 2 has an LED on D10 with a 220Ω resistor to GND, and an SG90 servo motor on D9 (signal), with VCC to the soldered 5V pin on Node 2’s XIAO-RP2040.
• Code Snippet (Sender - Node 1):

  void setup() {
      Serial1.begin(9600); // UART communication on D6 (TX) and D7 (RX)
      Serial.begin(115200); // For debugging on Serial Monitor
  }
  
  void loop() {
      // Send command to turn on LED
      Serial1.println("LED_ON");
      Serial.println("Sent: LED_ON");
      delay(2000);
  
      // Send command to move servo to 90 degrees
      Serial1.println("SERVO_90");
      Serial.println("Sent: SERVO_90");
      delay(2000);
  
      // Send command to turn off LED
      Serial1.println("LED_OFF");
      Serial.println("Sent: LED_OFF");
      delay(2000);
  
      // Send command to move servo to 0 degrees
      Serial1.println("SERVO_0");
      Serial.println("Sent: SERVO_0");
      delay(2000);
  }
                          

• Code Snippet (Receiver - Node 2):

  #include 
  
  Servo myservo;
  const int ledPin = 10; // D10 (GPIO 10) for LED
  String message = "";
  
  void setup() {
      Serial1.begin(9600); // UART communication on D6 (TX) and D7 (RX)
      Serial.begin(115200); // For debugging on Serial Monitor
      myservo.attach(9); // D9 (GPIO 9) for servo
      pinMode(ledPin, OUTPUT);
      digitalWrite(ledPin, LOW);
      myservo.write(0); // Start at 0 degrees
  }
  
  void loop() {
      while (Serial1.available()) {
          char incomingChar = Serial1.read();
          if (incomingChar == '\n') {
              if (message == "LED_ON") {
                  digitalWrite(ledPin, HIGH);
                  Serial.println("LED turned ON");
              } else if (message == "LED_OFF") {
                  digitalWrite(ledPin, LOW);
                  Serial.println("LED turned OFF");
              } else if (message == "SERVO_90") {
                  myservo.write(90);
                  Serial.println("Servo moved to 90 degrees");
              } else if (message == "SERVO_0") {
                  myservo.write(0);
                  Serial.println("Servo moved to 0 degrees");
              }
              message = "";
          } else {
              message += incomingChar;
          }
      }
  }
                          

• Result: The Serial Monitor on Node 2 displayed messages confirming the received commands (e.g., "LED turned ON", "Servo moved to 90 degrees"). The LED on Node 2 turned on and off as commanded, and the servo moved between 0 and 90 degrees.

Group Work Page Documentation

Documented the breadboard setup, wiring, code, and results on the group page.
Link to Group Work Page

Individual Reflection

Learned about wired communication using UART between XIAO-RP2040 boards. Collaboration was effective, but we faced issues with cross-talk between the UART lines, which were resolved by ensuring a solid common ground and reducing the baud rate to 9600.

Node Design and Build

• Designed the receiver node using the XIAO-RP2040 with an SG90 servo motor and an LED as outputs. The schematic and PCB layout were created in KiCAD.
• Schematic of the Node: li>
• Assembled the node on a custom PCB, with a pin soldered to the XIAO-RP2040’s 5V pin for the servo’s power.
• Components Used:
  • SG90 Servo Motor: To control a mechanical output.
  • 
  • LED: To provide visual feedback.
• Fabrication Check:
  • Design Rule Check (DRC): Ran DRC in KiCAD; found 3 spacing violations between traces near the I2C header (J2).
  • Adjustments: Increased the spacing between traces and rerouted the I2C lines to resolve violations.
  • Gerber Files: Gerber Files
  • Screenshot: Below is the PCB layout confirming fabrication readiness.
  • 

Network/Bus Configuration

• Configured the XIAO-RP2040 as the receiver node in a wired network using UART communication.
• Connected the receiver node (Node 2) to the sender node (Node 1) via UART: Node 1 TX (D6) to Node 2 RX (D7), Node 1 RX (D7) to Node 2 TX (D6), common GND between both boards.
• The sender node sends commands (e.g., "LED_ON", "SERVO_90") to the receiver node to control the LED and servo motor.

Local Input/Output Integration

• Integrated UART input from the sender node (Node 1) via the wired network, receiving commands to control the LED and servo.
• Integrated an SG90 servo motor to move to the specified angle (e.g., 0 or 90 degrees), connected to D9 (GPIO 9) on the J5 header for the signal, with VCC to the soldered 5V pin on the XIAO-RP2040.
• Integrated an LED to turn on or off, connected to D10 (GPIO 10) on the J5 header with a 220Ω resistor to GND.

Code Snippet

The code below configures the XIAO-RP2040 as the receiver node to control the servo and LED based on UART commands from the sender node.

#include 

Servo myservo;
const int ledPin = 10; // D10 (GPIO 10) for LED
String message = "";

void setup() {
    Serial1.begin(9600); // UART communication on D6 (TX) and D7 (RX)
    Serial.begin(115200); // For debugging on Serial Monitor
    myservo.attach(9); // D9 (GPIO 9) for servo
    pinMode(ledPin, OUTPUT);
    digitalWrite(ledPin, LOW);
    myservo.write(0); // Start at 0 degrees
    Serial.println("Receiver node initialized");
}

void loop() {
    while (Serial1.available()) {
        char incomingChar = Serial1.read();
        if (incomingChar == '\n') {
            if (message == "LED_ON") {
                digitalWrite(ledPin, HIGH);
                Serial.println("LED turned ON");
            } else if (message == "LED_OFF") {
                digitalWrite(ledPin, LOW);
                Serial.println("LED turned OFF");
            } else if (message == "SERVO_90") {
                myservo.write(90);
                Serial.println("Servo moved to 90 degrees");
            } else if (message == "SERVO_0") {
                myservo.write(0);
                Serial.println("Servo moved to 0 degrees");
            } else {
                Serial.println("Unknown command: " + message);
            }
            message = "";
        } else {
            message += incomingChar;
        }
    }
}
                

Node Code File: Node Code

Result

The XIAO-RP2040 receiver node successfully received commands via the wired network (UART) from the sender node. The LED turned on and off as commanded (e.g., "LED_ON" turned it on, "LED_OFF" turned it off). The SG90 servo motor moved to the specified angles (e.g., "SERVO_90" moved it to 90 degrees, "SERVO_0" moved it to 0 degrees). The Serial Monitor on the receiver node displayed messages confirming the actions (e.g., "LED turned ON", "Servo moved to 90 degrees").

Documentation

• Challenges: Initially attempted to use a water flow sensor and LCD, but both failed (reported on April 10, 2025). Switched to using an SG90 servo motor and an LED for the individual assignment. Powered the servo at 3.3V initially, which resulted in reduced torque; soldered a pin to the XIAO-RP2040’s 5V pin, improving performance. Faced issues with UART communication due to noise on the breadboard; resolved by ensuring a solid common ground and using a lower baud rate (9600).
• Hero Shot:
  • 
  • Description: This image shows the fabricated receiver node with the XIAO-RP2040 microcontroller (center), the SG90 servo motor connected to the soldered 5V pin, an LED on D10, and pin headers (J5) for UART connections to the sender node.
• Link to Group Assignment Page: The group assignment demonstrated wired communication using UART, which informed the individual assignment’s approach. Link to Group Work Page