Arduino EEPROM Read-Write Example

eeprom_rw_test.ino

/******************************************************

    Arduino EEPROM Read-Write Test
    by Ted Hayes 2012
    [email protected]
    
    Demonstrates the usage of the EEPROM Library for checking the state of a single value,
    changing it, and resetting it.  To use:
    
    1) Put a momentary switch between ground and pin 11 on your Arduino.
    2) Upload this program to it.
    3) Open the serial monitor
    4) You should see:
    Starting; current EEPROM value is 0
    EEPROM byte not set yet; Writing...
    Done.
    5) Now press the reset button on your Arduino and keep the serial monitor open.
    You should see:
    Starting; current EEPROM value is 1
    EEPROM byte was set!
    Done.
    6) Press your momentary switch, and you should see:
    Resetting EEPROM value
    7) Now press the reset button one more time, and you should see:
    Starting; current EEPROM value is 0
    EEPROM byte not set yet; Writing...
    Done.
    
    That's it!  Remember that the EEPROM on ATmega chips has a specified life of 100,000
    write/erase cycles, so be careful about putting writes/erases in loops, etc..

******************************************************/

#include <EEPROM.h>

#define PIN_SWITCH 11

int lastSwitch = HIGH;
boolean didReset = false;

void setup(){
  Serial.begin(9600);
  pinMode(PIN_SWITCH, INPUT);
  digitalWrite(PIN_SWITCH, HIGH); // set internal pull-up resistor
  
  int val = EEPROM.read(0);
  Serial.print("Starting; current EEPROM value is ");
  Serial.println(val);
  
  if(val != 1){
    Serial.println("EEPROM byte not set yet; Writing...");
    EEPROM.write(0, 1);
  } else if (val == 1){
    Serial.println("EEPROM byte was set!");
  }
  Serial.println("Done.");
}

void loop(){
  int currentSwitch = digitalRead(PIN_SWITCH);
  if(currentSwitch == LOW && lastSwitch != currentSwitch && !didReset){
    // switch has changed state
    // didReset is a simple form of debouncing, which prevents
    // this from being run too many times
    Serial.println("Resetting EEPROM value");
    EEPROM.write(0, 0);
    didReset = true;
  }
}