Arduino Code Not Processing Serial Output

Question

I am using a Arduino Uno for an embedded systems course. My assignment is that I have to write a function that implements these specifications. Take an input from the user (‘R’, ‘G’, ‘B’) and display Red, Green or Blue. The function name must be dispColor(), the input must be char a and their is no return. My code is below, however whenever I type in an input I receive no output. Where is the error in my code?

String dispColor(char){

  char a = Serial.read();

  if (a == "R")
    Serial.print("Red");
  else if (a == "G")
    Serial.print("Green");
  else if (a == "B")
    Serial.print("Blue");

}

void setup() {
// put your setup code here, to run once:
  Serial.begin(9600);
  String dispColor();
}

void loop() {
// put your main code here, to run repeatedly:

}

My Updated code

void dispColor(char a){
  if(Serial.available()){
        a = Serial.read();
        if(a == 'R')
        Serial.print("Red");
        else if(a == 'G')
        Serial.print("Green");
        else if(a == 'B')
        Serial.print("Blue");
    }
  }

void setup() {
    Serial.begin(9600);   
    Serial.println("Please type in R, G, or B.");
    dispColor();
}

void loop() {

}

Have you initialized Serial to begin with? If you did, are you sure you opened Serial in the same baudrate? — Miradil Zeynalli
– Miradil Zeynalli, Commented Oct 11, 2019 at 21:11
Use double quotes for strings e.g. "Red". Use single quotes for single characters, e.g. if (a == 'R') — user3386109
– user3386109, Commented Oct 11, 2019 at 21:13
Then it is as @user3386109 said. You dont compare strings, in a way you did. Using single quotes will solve the problem. If you want to compare strings, use strcmp function — Miradil Zeynalli
– Miradil Zeynalli, Commented Oct 11, 2019 at 21:16
Moreover, you wrote function as follows: function takes an argument of type char and returns a String. However, as you mentioned, function should not return anything so it should be void. Moreover, you should read Serial in loop and call that function while passing read charachter — Miradil Zeynalli
– Miradil Zeynalli, Commented Oct 11, 2019 at 21:19

Chris · Accepted Answer · 2019-10-11 21:35:10Z

1

As says the comment in setup ("// put your setup code here, to run once:", that code will be executed only once, so when you're ready to "type an input", there will not be any code running to read it.

Thus, one thing you'll definitely need to do is move dispColor to loop.

There are a few more mistakes:

You're comparing a char with a String
You should be passing a parameter to dispColor, not reading from within it
You should probably only be calling dispColor if there's input available.

Have a look at https://www.arduino.cc/reference/en/language/functions/communication/serial/read/ to get started!

answered Oct 11, 2019 at 21:35

Chris

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3 Comments

Chris Over a year ago

Please edit your question and add a new section with your updated code (don't modify the original code).

Angel Over a year ago

I've added another section with the updated the code.

Chris Over a year ago

It doesn't look like you've addressed any of the points I listed, but only added a check for whether a signal was available on the serial port. Please change your code to incorporate the points mentioned and post an update. If you don't understand something, feel free to ask specific questions!

Angel · Accepted Answer · 2019-10-12 22:08:17Z

0

I figured it out!

My new code

void setup() 
{
Serial.begin(9600);   
Serial.println("Please type in R, G, or B.");  
}

void dispColor(char a)
{
while(!Serial.available());
a = Serial.read();
 if(a == 'R')
    Serial.println("Red");
      else if(a == 'G')
    Serial.println("Green");
      else if(a == 'B')
    Serial.println("Blue");
    Serial.print('\n');
}

void loop() {
char a;
dispColor(a);

}

answered Oct 12, 2019 at 22:08

Angel

831 silver badge9 bronze badges

1 Comment

Chris Over a year ago

One thing that remains: you should read from Serial in loop and pass that as to dispColor - at the m.j moment you're ignoring (overwriting) the parameter a in dispColor.

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