Coding Debugging

There are a couple of issues:

• The function loop() doesn't return anything, by definition. Functions that do return a value return it with a statement like `return(someValue); Did you mean to say that it prints garbage on the terminal?

• If you want to print a value on the terminal, you need to use the the Serial.print(someValue) function; Serial.write() sends a binary value and that is probably not what you wanted. The binary values 0 - 9 represent non-printing characters so I'm not surprised that the terminal printed some odd graphic characters.

  -

That massive program can be compressed into just a handful of lines:

const int LED1 = 1, 
          LED2 = 3, 
          LED3 = 5;

void setup() {
    Serial.begin(9600);
    pinMode (LED1, OUTPUT);
    pinMode (LED2, OUTPUT);
    pinMode (LED3, OUTPUT);
}

void loop() {
    if (Serial.available()) {
        int x = Serial.read();
        x = x - '0';
        digitalWrite(LED1, x & 0x01);
        digitalWrite(LED2, x & 0x02);
        digitalWrite(LED3, x & 0x04);
        Serial.print(x);
    }
}

Note the use of Serial.print() not Serial.write(). If you use Serial.write() then it prints the ASCII character associated with the number you feed it - in your case characters 0 to 7 (none of which are printable).

Also, unless you check for there actually being something available for you to read from the serial you'll only get a brief flicker of something meaningful (too fast for the eye to see) and then it will just return -1, which with 48 subtracted from it would be -49, which would be "complete garbage".