Two way serial communication with raspberry Pi (radio project)

I removed some lines that are not used at the moment anyway:

/*
 * 
 * Siehe Arduino Cookbook: safari books online
 * Sends station numbers to Raspberri: ok
 * Receives max Numb of stations from Raspberry: nok
 */
const int MaxChars = 2;
char strValue[MaxChars+1];
int index = 0;
int maxNumb = 26;
int upperValue;
int lowerValue;
char ch;
int poti = 0;
int sensorValue = 10;
int tunerValue = 1;

void setup()                    // run once, when the sketch starts
{
  Serial.begin(9600);           // set up Serial library at 9600 bps
}

void loop()                       // run over and over again
{
 sensorValue = analogRead(poti);

 tunerValue = map(sensorValue, 0, 1023, 1, maxNumb);
  
  Serial.println(tunerValue,DEC);

delay(250);

if (Serial.available())
{
  char ch = Serial.read();
    if(index <  MaxChars && ch >= '0' && ch <= '9'){
      strValue[index++] = ch; // add the ASCII character to the string;
    }
    else
    {
      // here when buffer full or on the first non digit
      strValue[index] = 0;        // terminate the string with a 0
      maxNumb = atoi(strValue);  // use atoi to convert the string to an int
      index = 0;
    }
  }

}

At least at the built in serial console it does what I want it to do:

  • Starting with an initial value for the variable "maxNumb" (26) depending on the poti's position a number between 1 and 26 ist transfered via serial;
  • If I enter a different value in the console, maxNumb is updated; if for instance I enter 50, by turning the knob I can produce numbers between 1 and 50:

But I still have the problem, that I cannot use "echo" from my computer to fill this variable.