Bluetooth module(HC05) isn´t communicating correctly due to code or app related problems

[999]

Hello,
I have built an Arduino robotic arm following this link...

DIY Arduino Robot Arm with Smartphone Control

However instead of using an Arduino Uno as in the link, I used an Elegoo Mega. Accordingly I initialized the Bluetooth module (HC05) on pins 12 and 13 instead of pins 3 and 4.
I also adjusted the wiring on the board as required( not in 3 and 4).
The code compiles and uploads successfully, but when I check the communication using the serial monitor , I only receive trash.
Other people have suggested that the issue might not be with the Arduino Code but with the corresponding MIT App.
When I use the app and move the sliders to control the servo motors, nothing happens- even though the HC05 module is receiving data.
It seems like the arduino cannot interpret the data being sent correctly.
I am not very experienced in programming, so troubleshooting the issue is challenging for me.
The wiring matches the circuit diagram precisely, so I am unsure where the problem lies.
If someone could help me, I would greatly appreciate it.
(ideally with an explanation that is easy for a beginner to follow)
Thank you very much!!!!

Here is my code:

#include <SoftwareSerial.h>
#include <Servo.h>

Servo servo01;
Servo servo02;
Servo servo03;
Servo servo04;
Servo servo05;
Servo servo06;

SoftwareSerial Bluetooth(13 , 12); // Arduino(RX, TX) - HC-05 Bluetooth (TX, RX)

int servo1Pos, servo2Pos, servo3Pos, servo4Pos, servo5Pos, servo6Pos; // current position
int servo1PPos, servo2PPos, servo3PPos, servo4PPos, servo5PPos, servo6PPos; // previous position
int servo01SP[50], servo02SP[50], servo03SP[50], servo04SP[50], servo05SP[50], servo06SP[50]; // for storing positions/steps
int speedDelay = 20;
int index = 0;
String dataIn = "";
void setup() {

Serial.begin(38400);

  // put your setup code here, to run once:
 servo01.attach(5);
  servo02.attach(6);
  servo03.attach(7);
  servo04.attach(8);
  servo05.attach(9);
  servo06.attach(10);
  Bluetooth.begin(38400); // Default baud rate of the Bluetooth module
  Bluetooth.setTimeout(1);
  delay(20);
  // Robot arm initial position
  servo1PPos = 90;
  servo01.write(servo1PPos);
  servo2PPos = 90;
  servo02.write(servo2PPos);
  servo3PPos = 90;
  servo03.write(servo3PPos);
  servo4PPos = 90;
  servo04.write(servo4PPos);
  servo5PPos = 90;
  servo05.write(servo5PPos);
  servo6PPos = 90;
  servo06.write(servo6PPos);
  Serial.println("init ok");
}

void loop() {
  // put your main code here, to run repeatedly:
  // Check for incoming data
  if (Bluetooth.available() > 0) {
    dataIn = Bluetooth.readString();  // Read the data as string
    Serial.println("bluetooth ok");
    Serial.println(dataIn);

    // If "Waist" slider has changed value - Move Servo 1 to position
    if (dataIn.startsWith("s1")) {
      String dataInS = dataIn.substring(2, dataIn.length()); // Extract only the number. E.g. from "s1120" to "120"
      servo1Pos = dataInS.toInt();  // Convert the string into integer
      Serial.print("Servo 1: ");
      Serial.println(servo1Pos);
      // We use for loops so we can control the speed of the servo
      // If previous position is bigger then current position
      if (servo1PPos > servo1Pos) {
        for ( int j = servo1PPos; j >= servo1Pos; j--) {   // Run servo down
          servo01.write(j);
          delay(20);    // defines the speed at which the servo rotates
        }
      }
      // If previous position is smaller then current position
      if (servo1PPos < servo1Pos) {
        for ( int j = servo1PPos; j <= servo1Pos; j++) {   // Run servo up
          servo01.write(j);
          delay(20);
        }
      }
      servo1PPos = servo1Pos;   // set current position as previous position
    }
      // Move Servo 2
    if (dataIn.startsWith("s2")) {
      String dataInS = dataIn.substring(2, dataIn.length());
      servo2Pos = dataInS.toInt();
      Serial.print("Servo 2: ");
      Serial.println(servo2Pos);
      if (servo2PPos > servo2Pos) {
        for ( int j = servo2PPos; j >= servo2Pos; j--) {
          servo02.write(j);
          delay(50);
        }
      }
      if (servo2PPos < servo2Pos) {
        for ( int j = servo2PPos; j <= servo2Pos; j++) {
          servo02.write(j);
          delay(50);
        }
      }
      servo2PPos = servo2Pos;
    }
      // Move Servo 3
    if (dataIn.startsWith("s3")) {
      String dataInS = dataIn.substring(2, dataIn.length());
      servo3Pos = dataInS.toInt();
      Serial.print("Servo 3: ");
      Serial.println(servo3Pos);
      if (servo3PPos > servo3Pos) {
        for ( int j = servo3PPos; j >= servo3Pos; j--) {
          servo03.write(j);
          delay(30);
        }
      }
      if (servo3PPos < servo3Pos) {
        for ( int j = servo3PPos; j <= servo3Pos; j++) {
          servo03.write(j);
          delay(30);
        }
      }
      servo3PPos = servo3Pos;
    }
     // Move Servo 4
    if (dataIn.startsWith("s4")) {
      String dataInS = dataIn.substring(2, dataIn.length());
      servo4Pos = dataInS.toInt();
      Serial.print("Servo 4: ");
      Serial.println(servo4Pos);
      if (servo4PPos > servo4Pos) {
        for ( int j = servo4PPos; j >= servo4Pos; j--) {
          servo04.write(j);
          delay(30);
        }
      }
      if (servo4PPos < servo4Pos) {
        for ( int j = servo4PPos; j <= servo4Pos; j++) {
          servo04.write(j);
          delay(30);
        }
      }
      servo4PPos = servo4Pos;
    }
    // Move Servo 5
    if (dataIn.startsWith("s5")) {
      String dataInS = dataIn.substring(2, dataIn.length());
      servo5Pos = dataInS.toInt();
      Serial.print("Servo 5: ");
      Serial.println(servo5Pos);
      if (servo5PPos > servo5Pos) {
        for ( int j = servo5PPos; j >= servo5Pos; j--) {
          servo05.write(j);
          delay(30);
        }
      }
      if (servo5PPos < servo5Pos) {
        for ( int j = servo5PPos; j <= servo5Pos; j++) {
          servo05.write(j);
          delay(30);
        }
      }
       servo5PPos = servo5Pos;
    }
    // Move Servo 6
    if (dataIn.startsWith("s6")) {
      String dataInS = dataIn.substring(2, dataIn.length());
      servo6Pos = dataInS.toInt();
      Serial.print("Servo 6: ");
      Serial.println(servo6Pos);
      if (servo6PPos > servo6Pos) {
        for ( int j = servo6PPos; j >= servo6Pos; j--) {
          servo06.write(j);
          delay(30);
        }
      }
      if (servo6PPos < servo6Pos) {
        for ( int j = servo6PPos; j <= servo6Pos; j++) {
          servo06.write(j);
          delay(30);
        }
      }
      servo6PPos = servo6Pos; 
    }
     // If button "SAVE" is pressed
    if (dataIn.startsWith("SAVE")) {
      Serial.println("SAVE");
      servo01SP[index] = servo1PPos;  // save position into the array
      servo02SP[index] = servo2PPos;
      servo03SP[index] = servo3PPos;
      servo04SP[index] = servo4PPos;
      servo05SP[index] = servo5PPos;
      servo06SP[index] = servo6PPos;
      index++;                        // Increase the array index
    }
    // If button "RUN" is pressed
    if (dataIn.startsWith("RUN")) {
      Serial.println("RUN");
      runservo();  // Automatic mode - run the saved steps 
    }
    // If button "RESET" is pressed
    if ( dataIn == "RESET") {
      Serial.println("RESET");
      memset(servo01SP, 0, sizeof(servo01SP)); // Clear the array data to 0
      memset(servo02SP, 0, sizeof(servo02SP));
      memset(servo03SP, 0, sizeof(servo03SP));
      memset(servo04SP, 0, sizeof(servo04SP));
      memset(servo05SP, 0, sizeof(servo05SP));
      memset(servo06SP, 0, sizeof(servo06SP));
      index = 0;  // Index to 0
    }
  }
}
// Automatic mode custom function - run the saved steps
void runservo() {
  while (dataIn != "RESET") {   // Run the steps over and over again until "RESET" button is pressed
    for (int i = 0; i <= index - 2; i++) {  // Run through all steps(index)
      if (Bluetooth.available() > 0) {      // Check for incomding data
        dataIn = Bluetooth.readString();
        if ( dataIn == "PAUSE") {           // If button "PAUSE" is pressed
          while (dataIn != "RUN") {         // Wait until "RUN" is pressed again
            if (Bluetooth.available() > 0) {
              dataIn = Bluetooth.readString();
              if ( dataIn == "RESET") {     
                break;
              }
            }
          }
        }
        // If speed slider is changed
        if (dataIn.startsWith("ss")) {
          String dataInS = dataIn.substring(2, dataIn.length());
          speedDelay = dataInS.toInt(); // Change servo speed (delay time)
        }
      }
      // Servo 1
      if (servo01SP[i] == servo01SP[i + 1]) {
      }
      if (servo01SP[i] > servo01SP[i + 1]) {
        for ( int j = servo01SP[i]; j >= servo01SP[i + 1]; j--) {
          servo01.write(j);
          delay(speedDelay);
        }
      }
      if (servo01SP[i] < servo01SP[i + 1]) {
        for ( int j = servo01SP[i]; j <= servo01SP[i + 1]; j++) {
          servo01.write(j);
          delay(speedDelay);
            }
      }

      // Servo 2
      if (servo02SP[i] == servo02SP[i + 1]) {
      }
      if (servo02SP[i] > servo02SP[i + 1]) {
        for ( int j = servo02SP[i]; j >= servo02SP[i + 1]; j--) {
          servo02.write(j);
          delay(speedDelay);
        }
      }
      if (servo02SP[i] < servo02SP[i + 1]) {
        for ( int j = servo02SP[i]; j <= servo02SP[i + 1]; j++) {
          servo02.write(j);
          delay(speedDelay);
        }
      }

      // Servo 3
      if (servo03SP[i] == servo03SP[i + 1]) {
      }
      if (servo03SP[i] > servo03SP[i + 1]) {
        for ( int j = servo03SP[i]; j >= servo03SP[i + 1]; j--) {
          servo03.write(j);
          delay(speedDelay);
        }
      }
      if (servo03SP[i] < servo03SP[i + 1]) {
        for ( int j = servo03SP[i]; j <= servo03SP[i + 1]; j++) {
          servo03.write(j);
          delay(speedDelay);
        }
      }

      // Servo 4
      if (servo04SP[i] == servo04SP[i + 1]) {
      }
      if (servo04SP[i] > servo04SP[i + 1]) {
        for ( int j = servo04SP[i]; j >= servo04SP[i + 1]; j--) {
          servo04.write(j);
          delay(speedDelay);
        }
      }
      if (servo04SP[i] < servo04SP[i + 1]) {
        for ( int j = servo04SP[i]; j <= servo04SP[i + 1]; j++) {
          servo04.write(j);
          delay(speedDelay);
        }
      }

      // Servo 5
      if (servo05SP[i] == servo05SP[i + 1]) {
      }
      if (servo05SP[i] > servo05SP[i + 1]) {
        for ( int j = servo05SP[i]; j >= servo05SP[i + 1]; j--) {
          servo05.write(j);
          delay(speedDelay);
        }
      }
      if (servo05SP[i] < servo05SP[i + 1]) {
        for ( int j = servo05SP[i]; j <= servo05SP[i + 1]; j++) {
          servo05.write(j);
          delay(speedDelay);
        }
      }

      // Servo 6
      if (servo06SP[i] == servo06SP[i + 1]) {
      }
      if (servo06SP[i] > servo06SP[i + 1]) {
        for ( int j = servo06SP[i]; j >= servo06SP[i + 1]; j--) {
          servo06.write(j);
          delay(speedDelay);
        }
      }
      if (servo06SP[i] < servo06SP[i + 1]) {
        for ( int j = servo06SP[i]; j <= servo06SP[i + 1]; j++) {
          servo06.write(j);
          delay(speedDelay);
        }
      }
    }
  }
}

[ABG]

Regarding your project wiring, you might double check it against a bluetooth terminal app from the Play Store, to rule out AI2 problems.

I don't see you using any end of message delimiters like \n (decimal 10).

They are especially important when you are sending variable length message suffixes like thumb positions.

Check your development language library for verbs like ReadUntil to help grab only one message at a time.

This would require you to add '\n' to the ends of all messages sent either way.

Because of Bluetooth buffering, grabbing the entire conrtents of the incoming buffer might leave you with multiple messages in your String variable, and result in failure of any exact match attempts against your variable (unless you scan letter by letter.)

[Patryk_F]

@999

Serial.println(dataIn);

Make a test application, send some value, then show what the monitor displays using this function. We want to know exactly what you send and exactly what you receive.

@999

I only receive trash

This is not enough, but if these are strange characters, you may have the incorrect data transfer speed set here:

@999

Bluetooth.begin(38400); // Default baud rate of the Bluetooth module

Check what speed your BT module supports.

[999]

The baud rate seems to be set correctly. I tested it again and would like to explain the current status with a few images below:
1, Image 1 shows the output in the serial monitor when I try to control the robot via app.

2, the robot now responds to the movement of the sliders in the app(image 2). However, only one servo motor moves, specifically the Wrist Roll.

3, I tested all the other servos using a predefined Arduino code, and they all work perfectly. Still, they do not respond when I move the corresponding sliders in the app. Only the wrist roll moves.

4, I also tried using the readuntil() method. The result is shown in image 3 .
However, I am unsure whether I inserted the string correctly, as I have no prior knowledge of programming.

2

3

1

3

[ABG]

This can't be diagnosed without aia and ino files.

[Patryk_F]

To me it looks like a transmission speed problem, then such bushes appear. If I were you I would set it to 9600 instead of 38400. I think the default speed may depend on the manufacturer and may be different for different modules of the same type.

See this topic on how to adjust the speed to make sure it is that way.

HC-05 Bluetooth. Arduino. Change baud rate 38400. Send random to app

Hello friends, To carry out applications with Bluetooth between Arduino and App Inventor, the HC-06 module is usually used. This module can only work as a client, enough for most of the projects that you will see in the tutorials, it is the most used and recommended. Default 9600. [bluetooth1] Another similar module is the HC-05, this can function as a server or a client. You may have to set the speed using AT commands to adapt it to App Inventor. It comes with 38400 baud and you will have t…