2.5 Additional Exercise

2.5.1 Hardware Setup

You'll need:

• Camera/Webcam

• Jumper wires

• Arduino Nano (or Uno)

• USB cable to connect Arduino to PC

• External 5V power supply (if required)

• Red LED

• Blue LED

• 2 x 220Ω resistors

• Breadboard

Wiring:

• Connect the Red LED to digital pin 7 (with the resistor in series).

• Connect the Blue LED to digital pin 8 (with the resistor in series).

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2.5.2 Writing ROS Node

We will build system in ROS combine detection in face detection with Arduino LEDs. When face detected, the Blue Led will light up and Red Led will turn off, vise versa when no face detected.

Create a ROS package if you haven’t already:

source /opt/ros/foxy/setup.bash
cd ~/ros_ws/src
ros2 pkg create --build-type ament_python --node-name ser_facedetection ros_arduino_fd

cd ~/ros_ws/src/ros_arduino_fd/ros_arduino_fd
nano ser_facedetection.py

Before editing the python code, make sure already install all necessary python library.

sudo apt update
sudo apt install ros-foxy-rclpy ros-foxy-std-msgs
pip install opencv-python
pip install pyserial

code for python

ser_facedetection.py:

#!/usr/bin/env python3

import rclpy
from rclpy.node import Node
import cv2
import serial

class FaceDetectionNode(Node):
    def __init__(self):
        super().__init__('face_detection_node')
        
        # Setup serial communication with Arduino
        self.arduino = serial.Serial('/dev/ttyUSB0', 9600, timeout=1)  # Adjust the port accordingly
        self.arduino.flush()

        # Load OpenCV face detector (Haar Cascade)
        self.face_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_frontalface_default.xml')
        
        # Start video capture (webcam)
        self.cap = cv2.VideoCapture(0) #number based on your camera index: 0,1,2,3,4

        # Create a timer to run the face detection periodically
        self.create_timer(0.1, self.detect_face)

    def detect_face(self):
        # Capture frame from webcam
        ret, frame = self.cap.read()
        if not ret:
            self.get_logger().info("Failed to grab frame")
            return

        # Convert frame to grayscale
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

        # Detect faces
        faces = self.face_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbors=5, minSize=(30, 30))

        if len(faces) > 0:
            self.get_logger().info("Face detected")
            # Send command to Arduino for Blue LED (face detected)
            self.arduino.write(b'FACE_DETECTED\n')
        else:
            self.get_logger().info("No face detected")
            # Send command to Arduino for Red LED (no face detected)
            self.arduino.write(b'NO_FACE\n')

        # Display the frame with detection (optional for testing)
        for (x, y, w, h) in faces:
            cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 0), 2)
        cv2.imshow("Face Detection", frame)
        cv2.waitKey(1)

def main(args=None):
    rclpy.init(args=args)
    node = FaceDetectionNode()
    rclpy.spin(node)

    # Cleanup when shutting down
    node.cap.release()
    cv2.destroyAllWindows()

    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Make sure to modify /dev/ttyUSB0 to match the correct serial port for your Arduino.

Also look for your camera index and modify the code cv2.VideoCapture(0)

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2.5.3 Uploading Arduino Code

This Arduino code will receive commands via serial communication from the ROS 2 node and control the LEDs accordingly. Connect the Red LED to Pin 7 and the Blue LED to Pin 8.

Arduino Sketch:

const int redLedPin = 7;
const int blueLedPin = 8;

void setup() {
  // Initialize pins as outputs
  pinMode(redLedPin, OUTPUT);
  pinMode(blueLedPin, OUTPUT);

  // Initialize serial communication
  Serial.begin(9600);
}

void loop() {
  // Check if data is available from the serial
  if (Serial.available() > 0) {
    String command = Serial.readStringUntil('\n');

    if (command == "FACE_DETECTED") {
      // Turn on Blue LED, turn off Red LED
      digitalWrite(blueLedPin, HIGH);
      digitalWrite(redLedPin, LOW);
    } 
    else if (command == "NO_FACE") {
      // Turn on Red LED, turn off Blue LED
      digitalWrite(redLedPin, HIGH);
      digitalWrite(blueLedPin, LOW);
    }
  }
}

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2.5.4 Running the Code

1. Open a terminal on your PC and source ROS 2:

   source /opt/ros/foxy/setup.bash
   cd ~/ros_ws
   colcon build
   source install/setup.bash

2. Run the ROS node:

   ros2 run ros_arduino_fd ser_facedetection

Now you can see commands being sent from ROS to Arduino. Check the Arduino Serial Monitor to see the received data.

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