Interesting test: I was wondering if you could avoid the automatic string copy to RAM by putting strings inside a subroutine:

#include <avr/pgmspace.h>
int freeRam () {
  extern int __heap_start, *__brkval;
  int v;
  return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
}
void sub(void)
{
  char *text="ssssssssssssssssssssssssssssssss";
  Serial.print("inside function: ");
  Serial.println(freeRam());
//  text[0]='\0';
}
void setup() 
{
  Serial.begin(9600);
  Serial.println(freeRam());
  sub();
  Serial.println(freeRam());
}
void loop() 
{
}

Run it, and you’ll get a memory display of RAM before, during, and after the subroutine call, something like this:

1840
inside function: 1834
1840

But uncomment the line

//  text[0]='\0';

and run again – likely, you’ll get something more like this:

1806
inside function: 1800
1806

What happened? In the first one, the compiler optimized the text string right out of the system – until you did something with it (like setting text[0]) then it put it back in, and with a vengeance: that string is now in free memory RAM from the start of the program (notice the value before the subroutine was called – no change after).

What does this mean? If you use strings, be careful of them – anywhere they exist they add to RAM usage. Of course, if you move your strings to program memory, that’s another matter…