EEPROMに値を保存する

Normal variables live in RAM, which wipes clean the moment power drops. To keep a setting around, you need memory that remembers.

EEPROM is a small block of storage built into the chip that survives power loss. Think of it as a tiny notepad that stays written.

An Arduino Uno gives you about 1024 bytes of EEPROM. It is small, so save settings and counters, not big logs.

EEPROM is organized by numbered slots called addresses, starting at 0. You choose which address holds each value.

To use it, pull in the built-in EEPROM library at the top of your sketch. No download needed; it ships with the IDE.

EEPROM.write stores one byte at an address. Here we save the number 42 into slot 0.

EEPROM.read fetches the byte you stored. Read slot 0 and you get your value back, even after a reset.

A single byte stores values from 0 to 255. To save a larger number, you split it across several addresses.

For ints, floats, or structs, use EEPROM.put and EEPROM.get. They handle the byte splitting for you automatically.

EEPROM survives roughly 100,000 writes per cell. Don't write every loop, or you'll burn it out fast.

Use EEPROM.update instead of write. It skips the write when the value is unchanged, sparing the memory.

Let's check why we reach for EEPROM at all.

You saw EEPROM as non-volatile memory, wrote and read bytes by address, and learned to limit writes. Your settings can now persist! 💾