How to transmit a String to another Arduino over a Serial communication?(SOLVED)

Using Arduino Programming Questions
1

I have 2 Mega 2560.

I can transfer a byte between them. No problem.

However, when I transmit a String from A, B only receive a small portion of it. I really have no idea why? Please assist.

A sends to B

Serial2.write("LAT: 1.234567 LON: 102.987654");

B receives and display

while(Serial1.available()) {
       char b = Serial1.read();
       Serial.print(b);
}

From the above code, B only able to display "LAT". Can someone advice me why is that so? What happened to the rest of the String? However, if I change "char b" to "byte b", my output is as below:

766584583249465051525354553276797858324948504657565554535208

Thank you in advance.

2

From the above code, B only able to display "LAT". Can someone advice me why is that so?

I'm pretty sure that the fine folks at http://snippets-r-us.com can help you with your snippets.

Consider, though, that serial data transmission is ssslllooowww, and that the Arduino is fast. By the time the while loop starts, only a little bit of the data has arrived. By the time it ends, nothing more has arrived. If you want to receive the whole string, you have three choices.

  1. Make the string a fixed length, and wait for that number of characters to arrive.
  2. Add a delay between reading characters. That will give time for the next character to arrive. I recommend two weeks.
  3. Send a character that marks the end of the packet. Read and print (and store if there is a good reason for sending the data) the serial data until the end of packet marker arrives.

You can pound your head against the wall for as long as you like, but eventually you'll end up at choice 3 (unless you are zoomkat).

3

Thank you Paul!!!!

Option 1 and 3 is out of question. I added 1 millisecond delay and it works like charm!

Oh, and I apologise if you happen to not like it when I post snippet instead of the full codes.

So, yeah. After correction, the snippet is as below on B:

void setup() {
   Serial.begin(115200);
}

void loop() {
   while(Serial1.available()) {
          char b = Serial1.read();
          Serial.print(b);
          delay(1);
   }
}
4

Option 1 and 3 is out of question.

Nonsense. You own the code on both Megas. You CAN make the sender send a fixed length string or send an end of packet marker.

Serial2.println("LAT: 1.234567 LON: 102.987654");
There. The sender sends an end of packet marker (a carriage return and a line feed).

I added 1 millisecond delay and it works like charm!

I can promise that a change in baud rates IS going to bite you in the ass.

5

Sorry. I did not explain fully. The reason I said that earlier was because I had some concerns about the implementation of the codes in my current scenario, which is not simply,

Serial2.write("LAT: 1.234567 LON: 102.987654");

Nevertheless, from the way you said it, it seems sending a fix length or end of of packet marker is much better, I'll take a look at it, and update my codes accordingly. :slight_smile:

6

Some arduino to arduino test code that uses a comma , as a data packet delimiter.

//zoomkat 3-5-12 simple delimited ',' string tx/rx 
//from serial port input (via serial monitor)
//and print result out serial port
//Connect the sending arduino rx pin to the receiving arduino rx pin. 
//Connect the arduino grounds together. 
//What is sent to the tx arduino is received on the rx arduino.
//Open serial monitor on both arduinos to test

String readString;

void setup() {
  Serial.begin(9600);
  Serial.println("serial delimit test 1.0"); // so I can keep track of what is loaded
}

void loop() {

  //expect a string like wer,qwe rty,123 456,hyre kjhg,
  //or like hello world,who are you?,bye!,

  if (Serial.available())  {
    char c = Serial.read();  //gets one byte from serial buffer
    if (c == ',') {
      if (readString.length() >1) {
        Serial.print(readString); //prints string to serial port out
        Serial.println(','); //prints delimiting ","
        //do stuff with the captured readString 
        readString=""; //clears variable for new input
      }
    }  
    else {     
      readString += c; //makes the string readString
    }
  }
}