Arduino can't read Serial properly

Question

Alright, I've googled getting a string from Serial with Arduino and I've had no luck even copy and pasting examples.

I'm trying to get a string from the Serial. Here's my code:

void setup() {
    Serial.begin(9600);
    Serial.write("Power On");
}

void loop()
{
    while(!Serial.available());

    while (Serial.available() > 0) {
      Serial.write(Serial.read());
    }
    Serial.println();
}

And it's printing out character by character.

I also tried

char* read(int len) {
  while (!Serial.available());
  char str[len];
  int i = 0;
  while (i < len) {
    str[i] = '\0';
    int inByte = Serial.read();
    Serial.println(inByte);
    if (inByte == -1) {
        return str;
    } else {
      str[i++] = inByte;
    }
  }
  return str;
}

And it returns 1 character at a time (serial.print(inByte) gives -1 every other time). Why is the Serial splitting each character?

If I enter 'hello' and I call serial.read() it gives a character then says there's nothing, then gives another character and says there's nothing.

Solution 1

I figured it out.

When you open a Serial with 9600 baud (Serial.begin(9600);), it's reading/writing at 9600 bytes per second. That means at fastest it can get just under 10 bytes per millisecond. I don't know what the operating speed is, but it seems like the Arduino gets alerted of and reads the first byte before the second one arrives. So, you must add a delay(1) to "wait" for another byte in the "same stream" to arrive.

String read() {
    while (!Serial.available()); //wait for user input
    //there is something in the buffer now
    String str = "";
    while (Serial.available()) {
        str += (char) Serial.read();
        delay(1); //wait for the next byte, if after this nothing has arrived it means the text was not part of the same stream entered by the user
    }
    return str;
}

You may ask, well since you're delaying how do you know if the user is just typing very fast? You can't avoid it here, since the Serial is essentially limited at a certain speed. However, the user must be typing virtually-impossibly-fast for two inputs to be confused as one.

Solution 2

I don't have access to the Arduino source files here, but the following line of code won't give you a full String for obvious reasons (let me know if it's not that obvious):

int inByte = Serial.read();

Also, using

Serial.write()

you'll be sending byte per byte. That's the oposite from

Serial.println()

in which you'll be sending full sentences.

I would try working with Serial.print() or println() rather then Serial.write().

You can check out the references:

http://arduino.cc/en/Serial/Write

http://arduino.cc/en/Serial/Println

Solution 3

Even though this post is old, I'll post my answer in case someone googles their way here.

For reading strings from the serial you can use the following:

String str;

while (Serial.available() > 0) {
    str = Serial.readString();
}

Works like a charm!