Hi. I'm using ROS2 foxy with no libraries installed. It runs on an Ubuntu 21.04 x64 machine with kernel 5.8.0-59-generic.

I created a project with the goal of controlling an Arduino using python serial in a workspace with the following structure:

- workspace
    - src
        - arduino_comm
             - serial_server.py
             - serial_client.py
        - motor_interface
        - other_interface

the motor interface provides the action that is used by the arduino_comm package to send serial data. I have an old Arduino Nano that I've had for like 7 years ago that uses the old legacy bootloader. Still operational but sadly seems incompatible with the rosserial and I've checked the Micro-Ros packages and they also seem incompatible with my old arduino. Also I wanted to understand the code I'm working with at its bare basics before adding more complexity with an external library.

So I created the following code.

Arduino code

//Variable to store the bot command.
String botCommand;

void setup() {
  //Initialize Serial port.
  Serial.begin(9600);
  //Initialize BUILTIN LED to light up for feedback.
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  if(Serial.available()){
    botCommand = Serial.readString();
    if(botCommand == "forward"){
      //Light up the led.
      digitalWrite(LED_BUILTIN, HIGH);
      delay(10);
    }
    Serial.println(botCommand);
  }
  //Shut down the LED.
  digitalWrite(LED_BUILTIN, LOW);
  delay(10);
}

The Server and Client use the following action, which is based on the tutorial

##################################################
#Action that sends robot towards a specific spatial position.
##################################################
#Goal of achieving a specific position.
int32 botgoalposition
---
#Resulting position that we're aiming to attain.
int32[] botendposition
---
#Feedback message about current position.
int32[] botcurrposition

The arduino_comm serial_server.py dedicated to sending commands to the Arduino to follow.

import time
#Import the Serial library to send commands to Arduino.
import serial

#Elements required to generate an ActionServer.
import rclpy
from rclpy.action import ActionServer

#Library required to generate a ROS2 Node.
from rclpy.node import Node

##################################################
#                   ACTIONS
##################################################
#Action to calculate Fibonacci code. FOR DEBUGGING.
from code_interfaces.action import Fibonacci

#Action to send commands to the Arduino until it reaches the desired coordinates.
from bot_move.action import BotMove

#Class that encapsulates the Action Server.
class SerialCommServer(Node):
    def __init__(self):
        #Declare the Node with the name "serial server".
        super().__init__('serial_server')
        #Declare it'll be an ActionServer that publishes to the topic 'botmove'.
        self._action_server = ActionServer(
                self,
                BotMove,
                #Action name.
                'botmove',
                #Callback for executing accepted goals.
                self.executeCallback
                )

    #When it has been initialized, it'll start executing the following callback.
    def executeCallback(self, goalHandle):
        #Set the logger to indicate we're starting to execute our goal.
        self.get_logger().info('Executing goal...')

        #Get feedback to see if we're close to our goal.
        feedbackMsg = BotMove.Feedback()
        feedbackMsg.botcurrposition = [0,1]

        goalHandle.publish_feedback(feedbackMsg)

        #Send a small Hello to Arduino.
        arduino = serial.Serial(port="/dev/ttyUSB0")
        for i in range(1, 10):
            arduino.write(bytes(str("forward"), 'utf-8'))
            feedbackMsg.botcurrposition.append(i)
            self.get_logger().info('Feedback: {0}'.format(i))

            #Read back response from the Arduino.
            #TODO: THIS SECTION HANGS, NEED TO FIGURE HOW TO FIX IT.
#            response = arduino.readline()
#            print("Response: " + str(response ...