User Interface, Using A buffer with a module

Projects Programming
16 
radio.setFrequency(receivedChars[32]);

That will never work; no idea what it will do though. Why do you use a different approach as to

tft.println(receivedChars);

??

Anyway, you need to convert the text to a float. See man atof and man strtod; the former does not do error checking, the latter does.

void loop()
{
  float frequency;

  recvWithEndMarker();
  if (newData == true)
  {
    tft.fillScreen(BLUE);
    tft.print("You are listening to");
    tft.println(receivedChars);


    frequency = atof(receivedChars);
    radio.setFrequency(frequency);

    newData = false;
  }
}

I suggest that you use strtod (I'm a little lazy) and implement some error checking if it fails (tell the user that he's an idiot if he enters 'abc' instead of '123.45').

Note:
the above is based on the code in your reply #10.