Serial.read() giving very strange results

Projects Programming
1

This may be a basic question so please bear with me.

I'm running the following code below to better understand how the Arduino serial buffer works. The code is supposed to read a serial input string, character by character into a string variable, then serial.print that same string back to me.

String str;
int count=0 ;
char charBuffer;

void setup() {
  Serial.begin(9600);
}

void loop() {
  while (Serial.available()!= 0) {
  Serial.println("starting new while loop...");
  charBuffer = Serial.read();
  str += charBuffer;
  count+=1;
  }

  if (str != "") {Serial.println(str);str="";}
}

When I try to enter text into serial monitor (in this case "Arduino"), i get a weird result:

starting new while loop...
A
starting new while loop...
r
starting new while loop...
starting new while loop...
starting new while loop...
starting new while loop...
starting new while loop...
starting new while loop...
duino

I have 2 questions:

  1. How does Serial.read() interact with the serial buffer? My assumption is that it reads the first byte then discards it, which is how i implemented it in my code.

  2. Why is my code escaping the while loop, even with the condition while (Serial.available()!= 0) and the serial buffer not being exhausted yet?

3

Delta_G's answer is of course correct. To help you further understand the Problem:

You issued a Serial.begin(9600); command to initiate Serial communications at 9600 Baud (bits per second). A single Byte of data, such as "A" is 8 bits. Serial communication also has additional bits in the protocol (parity - but the Arduino is by Default NONE) and stop bits which add a "dead space" at the end of each Byte (by Default the Arduino uses 1). There is also a start bit. So... for a single character to be transmitted it will take

(8 + 1 +1 + 0) / 9600 =0.001041667 seconds - or just over a millisecond for each character to transmit. For a microcontroller running at 16MHz, a millisecond is a Long time...

4

You should look for a carriage return character before printing the string

5

You should be using if, not while.

The body of loop is expected to run very frequently, there's no point whatsoever in optimizing
the case of two serial bytes arriving spacing a few microseconds part (which is what using a while
loop is implying).

Generally loop()'s body should look like:

void loop()
{
  if (condition1) 
    handle_condition1 () ;
  if (condition2)
    handle_condition2 () ;
  ....
}

In other words its solely there to recognize when actions need to be performed and to do them.
Coding each action in a separate function is good style, it keeps loop() clean and free from any
detail that's specific to particular actions.

void loop()
{
  if (Serial.available() > 0)
    handle_serial () ;
  ...
  ...
}

void handle_serial()
{
  str += Serial.read();
  count+=1;
}

Note that doing things this way means you have a self-contained function for each action that
potentially can be reused from other places, and than combining several sketches into one is
much much easier.