WHat is wrong with Serial.println()

Projects Programming
1

void setup()
{
pinMode(13,OUTPUT);
Serial.begin(9600);
}

void loop()
{
while(Serial.available() == 0);

int i= Serial.read()-48;

if(i==1)
digitalWrite(13,HIGH);

else if(i==0)
digitalWrite(13,LOW);

else
Serial.println("invalid!");

}

Why does this code always show invalid no matter what the serial ip is???
the led (pin 13) works properly though...

2

The problem is not println the problem is the code. It was good to post the code, be sure to use the # icon above to put code tags around your code.

A book on C++ may be in order based on your code. Notice the code below - the if statement has the {} around it - very good practice and C++ 101.

Notice the output shows the result when not valid so you can see what is going on. When ever you have a question about the results of your code you should use serial.print to show the results. Now that you can see the results, making adjustments should be simple.

void setup()
{
  pinMode(13,OUTPUT);
  Serial.begin(9600);
}

void loop()
{
  while(Serial.available() == 0);
  
  int i= Serial.read()-49;
 
  if(i==1){
    digitalWrite(13,HIGH);
    
  } else if (i==0) {
    digitalWrite(13,LOW);
  } else {
    Serial.print("invalid ");
    Serial.println(i, DEC);
  }
}
3

Hey i tried out your code... there is a small mistake though it should be 48, so i changed that but still getting invalid...

int i= Serial.read()-48;

invalid -38
invalid -38
invalid 6
invalid -38

This is the output i got on the serial monitor for 3 inputs, The inputs were 1 0 6

4

Carriage return, line feed?

there is a small mistake though it should be 48,

No, it should be '0' .

5

What you should do is grab the actual value and show it / take action on the actual value. Why do you want to subtract a hard coded value?

Example: A or a turns on .... B or b turns off - else invalid.

void setup()
{
  pinMode(13,OUTPUT);
  Serial.begin(9600);
}

void loop()
{
  while(Serial.available() == 0);
  
  int i= Serial.read();
 
  //if A or B pressed
  if(i==97 || i==65){
    digitalWrite(13,HIGH);
    
  //if A or B pressed
  } else if (i==98 || i==66) {
    digitalWrite(13,LOW);
  } else {
    Serial.print("invalid ");
    Serial.println(i, DEC);
  }
}
6 
if(i==97 || i==65){

Isn't
if(i=='a' || i=='A'){ much easier to read?

7

thanx madworm, I had to select "no line end" in the serial monitor.... MY BAD :blush: