Sending data over Serial communication has 1 second delay

Projects Programming
1

Dear user of the forum,

I am currently doing a project where I am designing, and programming a scara robot completely from scratch. Currently I have the prototype design fabricated and ready to be used and I am now officially working on the software.

I managed to write software in C# (I wrote in C# due to experience gained during my education) which allows me to have a GUI and a G-code data converted. The way my software works is:

  • Reads G-code file
  • Manipulates data
  • Converts coordinates into stepper angles
  • Converts angles into steps
    When these steps are calculated they will be send in pairs of steps over the serial port in the following format: 100,50
    100 means stepper 1 should take 100 steps and 50 means stepper 2 should take 50 steps.
    When the stepper motor is done it will send the character x to the c# software which then knows the arduino is ready to recieve the new stepper position (See Arduino code below).

Now the problem that I have is that there seems to be a 1 second delay between the arduino sending the "x" character and the arduino recieving the new stepper positions from the C# software.

Do any of you know what I might be doing wrong in my code which causes this 1 second delay to occur? (Inverse kinematics calculations take place outside of the arduino on my laptop and only take about 0.004 seconds)

Arduino code:

#include <AccelStepper.h>

AccelStepper Motorjoint1(1, 2, 3); // pin 3 = step, pin 6 = direction
AccelStepper Motorjoint2(1, 8, 9); // pin 3 = step, pin 6 = direction

int movementdone = 0;

void setup() 
{
  Serial.begin(115200);
  Motorjoint1.setMaxSpeed(50000);
  Motorjoint1.setAcceleration(2000);
  Motorjoint1.setSpeed(200);
  //Motorjoint1.setCurrentPosition(300);
  Motorjoint2.setMaxSpeed(50000);
  Motorjoint2.setAcceleration(2000);
  Motorjoint2.setSpeed(200);
  //Motorjoint2.setCurrentPosition(-40);
}

void loop() 
{  
  if(Serial.available())
  {
    String holders = Serial.readString();
    int commaIndex = holders.indexOf(',');
    String joint1 = holders.substring(0, commaIndex);
    String joint2 = holders.substring(commaIndex +1, holders.length());

    int t1 = joint1.toInt();
    int t2 = joint2.toInt();
    
    Motorjoint1.moveTo((t1*4)*-1);
    Motorjoint2.moveTo((t2)*4); 

    while(abs(Motorjoint1.distanceToGo()) !=0 || abs(Motorjoint2.distanceToGo()) !=0 )
    {
      Motorjoint1.run();
      Motorjoint2.run();
    }
   
    if((Motorjoint1.distanceToGo() == 0) && (Motorjoint2.distanceToGo() == 0) && (movementdone == 0))
    { 
      movementdone++;     
      Serial.println("x");
    }
  }
}

C# communication code with arduino:

        private async void button1_Click(object sender, EventArgs e)
        {
            port = new SerialPort();
            port.PortName = "COM7";
            port.BaudRate = 115200;

            try
            {
                port.Open();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            if (port.IsOpen)
            {
                for(int i = 0; i < dataGridView1.RowCount - 1; i++)
                {
                    if(dataGridView1.Rows[i].Cells[2].Value.ToString().Contains(','))
                    {
                        DateTime t1 = DateTime.Now;
                        InverseKinematics InvKin_1 = new InverseKinematics(Convert.ToDouble(dataGridView1.Rows[i].Cells[2].Value), Convert.ToDouble(dataGridView1.Rows[i].Cells[3].Value));
                        string steps_to_take = Convert.ToString(Math.Ceiling(InvKin_1.Inverse_V2_Theta1()/0.45)) + ',' + Convert.ToString(Math.Ceiling(InvKin_1.Inverse_V2_Theta2()/0.45));
                        
                        System.Console.WriteLine(steps_to_take);
                        port.WriteLine(steps_to_take);
                        DateTime t2 = DateTime.Now;
                        TimeSpan t3 = t2 - t1;
                        System.Console.WriteLine(t3);
                        port.ReadLine().ToString().Contains("x");
                        
                    }
                }
                port.Close();
                MessageBox.Show("G-code finished");
            }
        }

Hopefully my explantation is clear and some of you might know what I am doing wrong.

Thank you in advance

-C

2

Try changing the timeout, or use a more responsive technique.

1 Like
3

The serial input basics tutorial shows robust ways to read and parse serial data without using the potentially problematic String class.

4

consider using readBytesUntil() recognizing the line terminator (\n or \r)

5

Thank you so much,

This is indeed the answer I was looking for. I didn't look into the Serial() data sheet. Turns out the default Serial.Timeout() is set to 1000 milliseconds. A quick change to 2 milli seconds (baudrate/max. amount of bits sent) solved the problem.

A simple change in the setup code showed how easy this solution actually was haha:

void setup() 
{
  Serial.setTimeout(2); //Milliseconds
  Serial.begin(115200);
  Motorjoint1.setMaxSpeed(50000);
  Motorjoint1.setAcceleration(2000);
  Motorjoint1.setSpeed(200);
  Motorjoint2.setMaxSpeed(50000);
  Motorjoint2.setAcceleration(2000);
  Motorjoint2.setSpeed(200);
}
1 Like
6

It's a sticking plaster rather than a solution; much better to use more robust methods, like looking for line endings, as mentioned.

7

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