part5_python_serial_arduino_ros.md

To See USB port in Ubuntu

lsusb

If serial port does not show in Arduino IDE on Ubuntu

sudo apt remove brltty 

Plug the arduino or dongle off and on

Arduino and Python Serial Communication Example

Python Code

import serial
import time

ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1)
time.sleep(0.1)

user_input = "L"

while user_input != 'q':
    user_input = input("H = LED ON, L = LED_OFF, q = Quit : ")

    byte_data = bytes(user_input, 'utf-8')
    byte_data_capitalize = byte_data.capitalize()
   
    ser.write(byte_data_capitalize) 
    time.sleep(0.5) 

for i in range(5):
    ser.write(b'H')   
    time.sleep(0.2)        
    ser.write(b'L')  
    time.sleep(0.2)

print('You entered q so, I am Exiting the program')

ser.close()

Arduino Code

const int ledPin = 13; 
int incomingByte;      // variable stores incoming serial data

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  if (Serial.available() > 0) {
    // read the oldest byte in the serial buffer:
    incomingByte = Serial.read();
    // if it's a capital H (ASCII 72), turn on the LED:
    if (incomingByte == 'H') {
      digitalWrite(ledPin, HIGH);
    }
    // if it's an L (ASCII 76) turn off the LED:
    if (incomingByte == 'L') {
      digitalWrite(ledPin, LOW);
    }
  }
}

ROS2 Humble node to control LED from turtlebot3 teleop_keyboard

Step 1: Make a node using the code. Arduino code will be same as before.

#! /usr/bin/env python3
import serial
import time

ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1)

#time.sleep(0.1)

user_input = "L"

import rclpy
from rclpy.node import Node
from turtlesim.msg import Pose
from geometry_msgs.msg import Twist

class PoseSubscriberNode(Node):

    def __init__(self):
        super().__init__("led_control_simple")
        self.get_logger().info("Pose Subscriber Node has been started")  
        #self.create_subscription(Twist,"/turtle1/cmd_vel", self.pose_callback, 10)
        self.create_subscription(Twist,"/cmd_vel", self.pose_callback, 10)


    def pose_callback(self, msg: Twist):
        # ros2 run turtlebot3_teleop teleop_keyboard
        # press W to ON Led and Press S to OFF Led 
        if msg.linear.x == 0.0:
            ser.write(b'L')
        if msg.linear.x > 0.0:
            ser.write(b'H')        

        self.get_logger().info(str(msg))



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

Step 2: Run teleop keyboard from the turtlebot3 package

ros2 run turtlebot3_teleop teleop_keyboard

Control a LED with Arduino: 1 ROS Node to Control and Publish LED State to a Topic and 1 ROS Node to Read LED State

Step 1:

First, we will create a Node name "led_control_simple" which will control Arduino LED and will make a topic name "led_state_publisher". This node will take keyboard input from Turtlebot3 teleop_keybaord. If we press 'W', the led will turn ON, and if we press 'S' it will turn OFF the led. To start the teleop keyboard

ros2 run turtlebot3_teleop teleop_keyboard

if you need to download turtlebot3 related package follow https://github.com/Nabilphysics/ros2/blob/main/part5_ros2_nav2.md
Code for our "led_control_simple" node is:

#! /usr/bin/env python3
import serial
import time

ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1)

#time.sleep(0.1)

user_input = "L"

import rclpy
from rclpy.node import Node
from turtlesim.msg import Pose
from geometry_msgs.msg import Twist
from std_msgs.msg import String

class PoseSubscriberNode(Node):

    def __init__(self):
        super().__init__("led_control_simple")
        self.get_logger().info("Pose Subscriber Node has been started")  
        #self.create_subscription(Twist,"/turtle1/cmd_vel", self.pose_callback, 10)
        self.publisher_ = self.create_publisher(String, 'led_state_publisher', 10)
        self.create_subscription(Twist,"/cmd_vel", self.pose_callback, 10)


    def pose_callback(self, msg: Twist):
        # ros2 run turtlebot3_teleop teleop_keyboard
        # press W to ON Led and Press S to OFF Led 
        led_state = "L"
        if msg.linear.x == 0.0:
            led_state = "L"
            ser.write(bytes(led_state, 'utf-8'))
            #ser.write(b'L')
        if msg.linear.x > 0.0:
            led_state = "H"
            ser.write(bytes(led_state, 'utf-8'))
            #ser.write(b'H')     
        led_topic_msg = String()
        led_topic_msg.data = led_state   
        self.publisher_.publish(led_topic_msg)    

        self.get_logger().info(str(msg))



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

Step 2: Create State Reader Node ""led_state_reader_node

import rclpy
from rclpy.node import Node
from std_msgs.msg import String

class PoseSubscriberNode(Node):

    def __init__(self):
        super().__init__("led_state_reader_node")
        self.get_logger().info("ed_state_reader_node Node has been started")  
        self.create_subscription(String,"/led_state_publisher", self.pose_callback, 10)
      


    def pose_callback(self, msg: String):
         

        self.get_logger().info(str(msg))

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

Step 3: Upload Arduino Code

const int ledPin = 13; 
int incomingByte;      // variable stores incoming serial data

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  if (Serial.available() > 0) {
    // read the oldest byte in the serial buffer:
    incomingByte = Serial.read();
    // if it's a capital H (ASCII 72), turn on the LED:
    if (incomingByte == 'H') {
      digitalWrite(ledPin, HIGH);
    }
    // if it's an L (ASCII 76) turn off the LED:
    if (incomingByte == 'L') {
      digitalWrite(ledPin, LOW);
    }
  }
}

Step 4: Edit setup.py file

from setuptools import setup

package_name = 'my_robot_controller'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='nabil',
    maintainer_email='nabil@cruxbd.com',
    description='www.nabilbd.com',
    license='TODO: License declaration',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
            "led_control_simple = my_robot_controller.led_control_simple:main",
            "led_state_reader = my_robot_controller.led_state_reader:main"
           
        ],
    },
)

Step 5: Build using colon build

cd ~/ros2_ws
colcon build --symlink-install

Step 6: Run these two nodes and turtlebot3 teleop keyboard

ros2 run my_robot_controller led_control_simple

ros2 run my_robot_controller led_state_reader

ros2 run turtlebot3_teleop teleop_keyboard

Now, if you press 'W' the led should be turned ON, and if you press 'S' the led should be turned OFF

How to monitor various topic

We can use a tool name rqt to visualize the data

rqt

then, Plugins Menu > Topics > Topics Monitor

How to publish data from rqt

rqt

then, Plugins Menu > Topics > Message Publisher