{"id":42267,"date":"2017-08-31T12:10:03","date_gmt":"2017-08-31T12:10:03","guid":{"rendered":"http:\/\/randomnerdtutorials.com\/?p=42267"},"modified":"2019-08-24T14:33:54","modified_gmt":"2019-08-24T14:33:54","slug":"arduino-eeprom-explained-remember-last-led-state","status":"publish","type":"post","link":"https:\/\/randomnerdtutorials.com\/arduino-eeprom-explained-remember-last-led-state\/","title":{"rendered":"Arduino EEPROM Explained – Remember Last LED State"},"content":{"rendered":"\n

This tutorial explains what is the Arduino EEPROM and what it is useful for. We\u2019re also going to show you how to write and read from the EEPROM and build a project example to put the concepts learned into practice.<\/p>\n\n\n\n

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We have a similar tutorial for the ESP32: ESP32 Flash Memory \u2013 Store Permanent Data (Write and Read)<\/strong><\/a><\/p>\n\n\n\n

Introduction<\/h2>\n\n\n\n

When you define and use a variable, the  generated data within a sketch only lasts as long as the Arduino is on. If you reset or power off the Arduino, the data stored disappears.<\/p>\n\n\n\n

If you want to keep the data stored for future use you need to use the Arduino EEPROM. This stores the variable\u2019s data even when the Arduino resets or the power is turned off.<\/p>\n\n\n\n

What is EEPROM?<\/h2>\n\n\n\n

The microcontroller on the Arduino board (ATMEGA328 in case of Arduino UNO, shown in figure below) has EEPROM (Electrically Erasable Programmable Read-Only Memory). This is a small space that can store byte variables.<\/p>\n\n\n\n

The variables stored in the EEPROM kept there, event when you reset or power off the Arduino. Simply, the EEPROM is permanent storage similar to a hard drive in computers.<\/p>\n\n\n\n

\"\"<\/figure><\/div>\n\n\n\n

The EEPROM can be read, erased and re-written electronically. In Arduino, you can read and write from the EEPROM easily using the EEPROM<\/span> library.<\/p>\n\n\n\n

How many bytes can you store?<\/h3>\n\n\n\n

Each EEPROM position can save one byte, which means you can only store 8-bit numbers, which includes integer values between 0 and 255.<\/p>\n\n\n\n

The bytes you can store on EEPROM dependson the microcontrollers on the Arduino boards. Take a look at the table below:<\/p>\n\n\n\n
Microcontroller<\/strong><\/td>EEPROM<\/strong><\/td><\/tr>
ATmega328 (Arduino Uno, Nano, Mini)<\/td>1024 bytes<\/td><\/tr>
ATmega168 (Arduino Nano)<\/td>512 bytes<\/td><\/tr>
ATmega2560 (Arduino Mega)<\/td>4096 bytes<\/td><\/tr><\/tbody><\/table>\n\n\n\n

However, if you need to store more data you can get an external EEPROM.<\/p>\n\n\n\n

The EEPROM finite life<\/h2>\n\n\n\n

The EEPROM has a finite life. In Arduino, the EEPROM is specified to handle 100 000 write\/erase cycles for each position. However, reads are unlimited. This means you can read from the EEPROM as many times as you want without compromising its life expectancy.<\/p>\n\n\n\n

Applications in Arduino projects – Remember last state<\/h2>\n\n\n\n

The EEPROM is useful in Arduino projects that need to keep data even when the Arduino resets or when power is removed.<\/p>\n\n\n\n

It is specially useful to remember the last state of a variable or to remember how many times an appliance was activated.<\/p>\n\n\n\n

For example, imagine the following scenario:<\/p>\n\n\n\n