Not clear the meaning of Serial.available() function.
Can someone help!?
thanks
It tells you how many characters are available in the receive buffer for you to read.
See - http://arduino.cc/en/Serial/Available -
Tip: never read more bytes (chars) than Serial.available() indicates 
So, typing:
if (Serial.available()==3){
...
}
Arduino gets data from computer, if you insert three characters only?
is that correct?
Yes, but the problem is, if you don't check often enough, you may find that you have found four characters available, and the test will fail.
= 3 would be a better test.
Thanks a lot!
but, sorry, for me it's still a bit misleading...
//in this case:
void loop(){
if (Serial.available()>2){
int inByte=Serial.read();
Serial.println(inByte);
}
}
/* after uploading the sketch, typing a number of char, in the serial window, lower than 3,
no replies are obtained.
actually, after 4 or more characters are entered, even if just new one is typed, Arduino sends the corresponding
ASCII code back.
How can I change the sketch, so only if 2 or more characters are entered, replies are sent, at any moment?
I hope i've been clear...*/
typing a number of char, in the serial window, lower than 3,
no replies are obtained.
Think about what you have.
Imagine you start "loop" with three characters in the buffer.
Think about what will happen to Serial.available after you have read out one character.
/* after uploading the sketch, typing a number of char, in the serial window, lower than 3,
no replies are obtained.
The Arduino does not have a serial window. The PC has an application called Serial Monitor that the Arduino IDE can launch.
That Serial Monitor application may, or may not append data to the serial stream it is sending, depending on what (unspecified) option you have selected.
That application does not send data as you type. It sends data only when you press the enter key or press the send button.
It would be really helpful if you would explain what application you are using to send the data, what options you have set, and how, exactly, you are sending the data.
It would be really helpful if you would explain what application you are using to send the data, what options you have set, and how, exactly, you are sending the data.
To send data to Arduino, i use the serial monitor launched from the Arduino IDE.
My purpose is to send ASCII codes (so composed by one ore more digits) to Arduino and get back the corresponding character....is it possible...?
Think about what you have.
Imagine you start "loop" with three characters in the buffer.
Think about what will happen to Serial.available after you have read out one character.
I'm not able to figure it out...no ideas..
I'm not able to figure it out.
Imagine you start "loop" with three characters in the buffer.
You see that Serial.available returns three.
Three is greater than two, so you read one character out.
"loop" exits, gets called again, and you call Serial.available again
What happens next?
The best ratio of answers to questions is 1. Higher than 1 is much better than lower than 1.
Now, we know that you are using the Serial Monitor application, but not what options you have set, what you are sending or when.
My purpose is to send ASCII codes (so composed by one ore more digits) to Arduino and get back the corresponding character....is it possible...?
Yes, it is. It is quite easy, in fact.
There are two ways to go about it. One is to always send three characters, and hope like hell none get lost (not a realistic thing to do). The other is to send the value followed by a delimiter. The Serial Monitor makes this option easy.
Then, you read the data on the Arduino, storing it in a NULL terminated char array until the delimiter arrives. When that happens, you convert the array contents to an int, using atoi(), send a response, and reset the array index to 0 and put a NULL in that position of the array.
Though why you want to do this, versus looking in an ASCII table, is unclear.
Imagine you start "loop" with three characters in the buffer.
You see that Serial.available returns three.
Three is greater than two, so you read one character out.
"loop" exits, gets called again, and you call Serial.available again
What happens next?
void setup(){
Serial.begin(9600);
}
void loop(){
if(Serial.available()>2){
char inBytes=Serial.read();
Serial.println(inBytes);
}
}
first three characters typed:
"567"
Serial returns
"5"
(as you said)
going on with serial input, for example with
"sg89"
i get
"67sg"
ecc...
so, opening for the very first time the serial monitor, while less than 3 char are typed,
no signal is returned. When 3 or more char are entered, serial data began to flow from Arduino to pc.
Buffer does not reset each time the loop() cycle begin, for this reason, just when i open for the first time the serial port, this happens.
Right?...
my goodness, i'm sweating...
I don't see anything in your observations that I don't expect.
What are you expectations?
When 3 or more char are entered, serial data began to flow from Arduino to pc.
No, it does not. No serial data is sent until you press the Send button or hit the enter key.
Buffer does not reset each time the loop() cycle begin
True. It would be useless if it did.
just when i open for the first time the serial port, this happens.
No. The buffer is cleared because opening the serial port resets the Arduino. The buffer is set up after the reset, empty.
my goodness, i'm sweating...
You wouldn't be here. It's freezing.
When 3 or more char are entered, serial data began to flow from Arduino to pc.
No, it does not. No serial data is sent until you press the Send button or hit the enter key.
Yep, sorry, i meant "after pressing" enter key...
I don't see anything in your observations that I don't expect.
What are you expectations?
i was trying to get the meaning of Serial.available function, and what seem to be obvious statements,
for my experience, are enormous obstacles!
Thanks foor helping me, Your all advices have been precious for me!
PaulS:
You wouldn't be here. It's freezing.
Where I am it is 10 pm, 28 C (82 F). It's hot, man!
Think of Serial.available as a little guy who sits in your letter box, who tells how many letters there are in the box when you ask him.
If you take a letter out of the box (Serial.read) there's one fewer letter in the box, so next you ask Serial.available, he reports one fewer than last time you asked.
If you decide that you're only going to take out letters when there are three or more letters in the box.
You ask Serial.available, and he says "three".
So, you take one letter.
Then you ask again, and he says "two", so you don't take any letters.
If you decide that you're only going to take out letters when there are three or more letters in the box.
You ask Serial.available, and he says "three".
So, you take one letter.
Then you ask again, and he says "two", so you don't take any letters.
So, the trick here is when the little guy says that there are three letters, you need to take three.
Keep in mind that you still have not answered the question about what option you have chosen for the Serial Monitor, so if you type three characters and hit enter, there may be 3, 4, or 5 characters actually sent to the Arduino.
But, the idea that, because there are three or more characters to read, the characters represent a packet, and nothing but a packet is flawed. Serial data is not guaranteed to be delivered. A byte could have gotten corrupted for any number of reasons.
What you should be doing is having the Serial Monitor append something to the string you send. Then, you read and store each character that is available, followed by a NULL, unless that character is one that was added by the Serial Monitor. If it is, then the stored data is of interest, so you use it, and reset the index that defines where in the array you are storing data, along with NULLing the first element off the array.
Keep in mind that you still have not answered the question about what option you have chosen for the Serial Monitor, so if you type three characters and hit enter, there may be 3, 4, or 5 characters actually sent to the Arduino.
after uploading the program on Arduino, I open the serial monitor, digit characters inside the communication field, and hit enter. That's it.
Referring to the following code:
int input;
void setup(){
Serial.begin(9600);
}
void loop(){
if(Serial.available()>=3){
char input=Serial.read();
Serial.println(input);
Serial.println("what serial.available contains:");
Serial.println(Serial.available());
}
}
if i enter "567", the Serial.print function returns "5"; that because, characters are sent to Arduino one by one, so when the first digit is sent, the if statement goes like that: "the first char enter the Arduino buffer. Now the Arduino buffer contains >= 3 elements? = NO! and so on, until i enter"7".
Now Arduino buffer contains 3 or more elements so 'if loop' is triggered, and Serial.read reads the first element stored in the buffer, that is "5"! Printing the element (Serial.available) left in the buffer, the answer is "2", and that is trivial...
But going on in the same serial monitor, typing other three char, for example "890": this is the signal returned:
6
what serial.available contains:
2
7
what serial.available contains:
3
8
what serial.available contains:
2
why after "7" character has been read, there are 3 elements left in Arduino buffer!?
I asked a very simple question. What option have you selected at the bottom of the Serial Monitor dialog? I'm not going to participate in this discussion any more until you answer that question.