How to write a float value EEPROM

Question

I'm using this library for my DS3231 which have a Atmel 24C32 on it. i have a float value which increases by 0.5, like:

27.50

28

28.50 ...

the code is like this:

float lowTemp= 10.5

float highTemp= 10.5

void setup(){
  lowTemp = i2c_eeprom.read(100);
  highTemp = i2c_eeprom.read(101);
}
void loop(){
  if ((menuswtichStatus == HIGH) && (lcdWelcome == HIGH)) {
    previousMillis = millis();
    lcd.clear();
    menuScroll++;
    lcdClear = 1;
    lcdClear2 = 1;
  }
  if (menuScroll == 1) {
    lcd.setCursor(0, 0);
    lcd.print("Temperature set:");
    lcd.setCursor(0, 1);
    lcd.print("Minimum  ");
    lcd.print(lowTemp);
    lcd.print((char)223);
    lcd.print("C ");
    if (plusSwitchstatus == HIGH) {
      lowTemp += 0.5;
    }
    if (minusSwitchstatus == HIGH) {
      lowTemp -= 0.5;
    }
  }
  if (menuScroll == 2) {
    lcd.setCursor(0, 0);
    lcd.print("Temperature set:");
    lcd.setCursor(0, 1);
    lcd.print("Maximum  ");
    lcd.print(highTemp);
    lcd.print((char)223);
    lcd.print("C ");
    if (plusSwitchstatus == HIGH) {
      highTemp += 0.5;
    }
    if (minusSwitchstatus == HIGH) {
      highTemp -= 0.5;
    }
  }
  if (menuScroll == 3) {
    lcd.setCursor(0, 0);
    lcd.print("   Saving the");
    lcd.setCursor(0, 1);
    lcd.print("   Settings...");
    delay(1000);
    i2c_eeprom.write(100, lowTemp);
    i2c_eeprom.write(101, highTemp);
    delay(1000);
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("    SETTINGS");
    lcd.setCursor(0, 1);
    lcd.print("     SAVED!");
    delay(2000);
    menuScroll = 0;
    lcdClear = 0;
    lcdClear2 = 0;
  }
}

i have the library and stuff up there, it's just an example of my code...

The float value is not saving(written), what's the solution?

Answer 1

You have multiple options:

1. According to jsotola's remark: the easiest is to multiply your value by 2, store it, and after reading, divide it by 2. In one byte you can store a value from 0 to 127.5 (255 / 2), or if you use signed from -64.0 to +63.5. Of course you also can use an offset in case you know the value cannot be less than e.g. -20.
2. If you need a higher range, you can still multiply it by 2, but store it in two bytes. Split the value in a 'high value' (value % 256) / 256, and a 'low value' (value % 256).
3. If you want to store the value completely, than use sizeof(float) to find the length, and a for loop to write each byte, starting from the first byte of the float until the last one.