Asked — Edited

Triggering UART At Travel Milestones

Hello @Athena,

I'm working on a project using an Arduino Mega 2560 to control stepper motors and need help with setting up recurring events that trigger at specific points during the movement. Specifically, I want to send a signal when the motors have traveled 33% and 66% of the total path endpoint distance. Here's a code snippet representing the loop where I'd like to incorporate these triggers:

int pathEndpointDistance = 2100;

while (LeftFrontWheel.currentPosition() + RightFrontWheel.currentPosition() <= pathEndpointDistance) {

}

For each of these trigger events, I need to send the character 'O' via UART, so it can be received and processed by my EZ-B v4, which is currently running a JavaScript script. Could you please provide guidance on how to write the C++ code necessary to send the character 'O' via UART at the 33% and 66% progress milestones relative to pathEndpointDistance?

Thank you for your assistance.

Best regards,
Jack


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#1  

Hi Jack,

Let's work through how you can achieve sending the character O at 33% and 66% of the total path distance.

Based on your description, you have a total path distance defined as:

pathEndpointDistance = 2100

And you want to trigger at:

33% trigger: 2100 * 0.33
66% trigger: 2100 * 0.66

You'll need to check the current travel distance during your movement loop and, when the motor positions pass these percentages, send the character O via UART. The key is to use flags so that each trigger sends the character only once.

Below is a sample C++ snippet for your Arduino Mega 2560:


int pathEndpointDistance = 2100;  // Total distance of the path
bool trigger33Sent = false;       // Flag for 33% trigger
bool trigger66Sent = false;       // Flag for 66% trigger

// Example function to get the combined travel distance - adjust as needed.
// Here, it's assumed that LeftFrontWheel.currentPosition() and
// RightFrontWheel.currentPosition() return a value representing the traveled distance.
// You might want to average or sum them based on your actual setup.
int getCurrentDistance() {
  return LeftFrontWheel.currentPosition() + RightFrontWheel.currentPosition();
}

void loop() {
  // Read the current traveled distance.
  int currentDistance = getCurrentDistance();

  // Check if we have reached or passed 33% of the path.
  if (!trigger33Sent && currentDistance >= (pathEndpointDistance * 0.33)) {
    Serial.write('O');   // Send character O via UART
    trigger33Sent = true;
  }

  // Check if we have reached or passed 66% of the path.
  if (!trigger66Sent && currentDistance >= (pathEndpointDistance * 0.66)) {
    Serial.write('O');   // Send character O via UART
    trigger66Sent = true;
  }

  // Continue your loop until you reach the endpoint.
  if (currentDistance >= pathEndpointDistance) {
    // Optionally, handle completion of the travel
  }

  // Other movement or processing code goes here...
}

Explanation

  1. Flags for Triggers:
    Two Boolean flags (trigger33Sent and trigger66Sent) ensure that each event is only triggered once.

  2. Current Distance:
    The function getCurrentDistance() should represent how you calculate progress along the path. In this example, I simply summed the positions from both wheels. Depending on your setup (e.g., if both wheels are moving in tandem or if you need an average instead), you might need to adjust this calculation.

  3. UART Transmission:
    The Serial.write('O'); statement sends the character O via the Serial (UART) interface. Make sure the Serial interface is correctly initialized in your setup() function (e.g., with Serial.begin(baudRate);).

  4. Incorporating with ARC:
    On the ARC (EZ-Builder) side, your JavaScript script can listen for the character O. This will let you process the trigger events accordingly using ARC’s JavaScript functionalities.

Next Steps

  • Verify that your motor functions (e.g., LeftFrontWheel.currentPosition()) return values in the expected units.

  • Ensure that you initialize the Serial port in your Arduino setup():

    void setup() {
      Serial.begin(115200); // Adjust the baud rate if necessary
      // Other initialization code...
    }
    
  • Test the code in a safe environment to ensure that the triggers are activated at the correct milestones.

Let me know if you have any further questions or need adjustments based on how your motors behave or how the data is processed in ARC's JavaScript!


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