Save app data

Generally, you will be needing to use real, or simulated EEPROM.

The EEPROM library contains all that you will need.

I always put data that I want stored between sessions into a user-defined structure, it makes life really simple ...

// Create the EEPROM data structure
struct udt_eeData {
int16_t   runaway_time;     // seconds
int16_t   gassing_time;     // seconds
uint8_t   id;               // this is last to catch structure changes
};

then you have to create an "instance" data of that declared structure ...

//Create the EEPROM data of type udt_eeData
udt_eeData eeData;

Read your data using EEPROM.get(eeData) reads the whole of the data you declared.

In the example above, the saved "gassing_time" is addressed as "eeData.gassing time".

I use the "id" member of the user-defined structure to detect structure changes, or i can force a change in my code by changing it before compilation, sort of like a "build" number. Use it to assert "default" values.

  // initialise eeData if NOT already present
  // THIS SHOULD ONLY OCCUR IF BUILD has changed !!
  if (eeData.id != build_no) 
    {
    eeData.runaway_time = 30;
    eeData.gassing_time = 3;  
    eeData.id = build_no;
    EEPROM.put(eeAddress, eeData);
    EEPROM.commit(); // only needed for virtual EEPROM
    }

Write data to the EEPROM using EEPROM.put(eeData).  This function only writes to the EEPROM any bytes that have changed, prolonging the EEPROM write-cycle lifetime.

Any questions ? Please ask... I've used this technique on several projects, with huge success .....