[SOLVED] Negative input into Serial Monitor

[JDM]

Hi. Can anyone tell me on how can i put a negative number into the serial monitor? Everytime i put a -1 (for example), this happens:

Screen Shot 2012-11-06 at 1.30.05 PM.png (18.21 KiB) Viewed 2478 times

It seems that the serial monitor reads a minus sign as -3, then read 1 as 1 (which is correct, except the negative sign).

Here's the code:

CODE: SELECT_ALL_CODE

void loop() {

     while (!Serial.available());   // wait until there was signal send from computer
     inByte = Serial.read();
     inByte = inByte-48;        // minus 48 (30 hex) to get the decimal value (got from Cytron tutorial)

     Serial.print("I received: ");
     Serial.println(inByte);
               
}


I've been googling around but not yet found any solution

[shahrul]

inByte is char (8 bit value)

Then you type '-' & '1'. 2 character.
ASCII for '-' equal to 45. Then 45 minus 48, it get -3.

[JDM]

Oooo i see. Now i understand. Thanks!

Any idea on how i can make it to read 2 character at once?

[shahrul]

You do if(Serial.available()); first.
Then while (!Serial.available())
{what_ever_code_here();};

[JDM]

Thanks!

BTW after playing around with your recommendation, this is what i've done to differentiate between a negative & positive input.

CODE: SELECT_ALL_CODE

    inByte = Serial.read();
   
    if (inByte == 45) {                     // read negative input. -ve == 45
      while (!Serial.available());          // wait until there was signal send from computer
      inByte = Serial.read();
      inByte = -(inByte-48);                // minus 48 (30 hex) to get the decimal value
      Serial.print("I received: ");
      Serial.println(inByte);
    }
 
    if (inByte > 45) {                      // read positive input
      inByte = inByte-48;
      Serial.print("I received: ");
      Serial.println(inByte);
    }


Thanks again!