How to free up more memory

Using Arduino Programming Questions
1

Hi!
I am creating an Arduino based smart watch, and I am having problems with memory.
The majority of my code is fine and doesn't take up that much space, however the timing sequence that reads the time from a Sparkfun DS1307 and projects the time on a Freetronics OLED board is taking up a huge chunk of my memory (around 30%). I was wondering if anyone had any tips on how to cut down some space. Any help/advice would be greatly appreciated :slight_smile:

Below is the timing sequence code:

  DateTime now = RTC.now();
  String writeString;
  time.setForegroundColour(WHITE);
  writeString = "";
  writeString += String(now.hour());
  writeString += ":";
  writeString += String(now.minute());
  oled.selectFont(Droid_Sans_36);
  time.print(writeString);
  time.reset();

  writeString = "";
  writeString += String(now.day());
  writeString += "/";
  writeString += String(now.month());
  writeString += "/";
  writeString += String(now.year());
  date.setForegroundColour(WHITE);
  oled.selectFont(SystemFont5x7);
  date.print(writeString);
  date.reset();
2

You could try not using the String class.

3

AWOL has given you some good advice. This program (I don't have a RTC) is based on your use of the String class:

#define GOOD      // Comment this line out to get bad version

#ifdef GOOD
char writeString[20];
#else
String writeString;
#endif

#ifdef GOOD
void UseCharArray()
{
  writeString[0] = '\0';
  strcat(writeString, "10");
  strcat(writeString, ":");
  strcat(writeString, "59");

  Serial.println(writeString);

  writeString[0] = '\0';
  strcat(writeString, "Saturday");
  strcat(writeString, "/");
  strcat(writeString, "April");
  strcat(writeString, "/");
  strcat(writeString, "2017");
  Serial.println(writeString);
}
#else
void UseStringClass()
{
  writeString = "";
  writeString += "10";
  writeString += ":";
  writeString += "59";

  Serial.println(writeString);

  writeString = "";
  writeString += "Saturday";
  writeString += "/";
  writeString += "April";
  writeString += "/";
  writeString += "2017";
  Serial.println(writeString);
}
#endif

void setup() {
  Serial.begin(9600);

#ifdef GOOD
  UseCharArray();     // Use C strings
#else
  UseStringClass();   // Use String class
#endif
}

void loop() {
}

It uses 3298 bytes of flash memory and 232 bytes of SRAM. If you uncomment the #define at the top, the code using C strings (i.e., lower case 's' using character arrays) compiles to 1918 bytes of flash and 235 bytes of SRAM.

4

...And you could maybe Improve on that by better use of flash memory

5

Thankyou for the quick responses! I'll give it a try

6

Will using std c string library instead of String class to manipulate strings usually save memory ?

7

noweare:
Will using std c string library instead of String class to manipulate strings usually save memory ?

Yes.