43. Project: EEPROM Settings

This lesson uses: Arduino UNO R3 board, TinkerBlock TK31 EEPROM module, TinkerBlock TK04 Push Button module, TinkerBlock TK01 XL LED module, jumper wires (or breadboard). Project: save LED on/off state in EEPROM; outcome: button toggles LED and writes state to EEPROM; after power off and on, state is read from EEPROM and LED is restored.

1. Project goal

Build a settings-save system:

• Press button: change LED state and save to EEPROM
• Power on again: read last state from EEPROM and restore LED

2. Wiring

• TK31 EEPROM: GND → GND, VCC → 5V, SDA → A4, SCL → A5
• TK04 Button: VCC → 5V, GND → GND, SIGNAL → D2
• TK01 LED: GND → GND, SIGNAL → D13

3. Program structure

Same as last lesson: two fixed blocks setup() and loop().

• setup(): Include library, init, read last state from EEPROM, restore LED; runs once.
• loop(): Keep repeating “detect button → change state → save to EEPROM → wait → repeat”.

Button changes LED state and it is stored in EEPROM; after power cycle the LED returns to the last state.

4. Code to write

Type the code below at the top of the file and in setup() and loop() (do not copy-paste; typing it yourself helps you remember):

// EEPROM save LED state: button toggles and writes; on power-up read and restore
#include <Wire.h>
#define EEPROM_ADDR 0x50   // TK31 I2C address
#define BUTTON_PIN 2
#define LED_PIN 13

int lastButtonState = HIGH;
bool ledState = false;

void setup() {
  Wire.begin();   // I2C init (SDA=A4, SCL=A5)
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  
  // Read last state from EEPROM
  byte savedState = readEEPROM(0);
  ledState = (savedState == 1);
  digitalWrite(LED_PIN, ledState ? HIGH : LOW);
  
  Serial.print("Restored: LED ");
  Serial.println(ledState ? "on" : "off");
}

void loop() {
  int buttonState = digitalRead(BUTTON_PIN);
  
  // Button press (HIGH -> LOW)
  if (buttonState == LOW && lastButtonState == HIGH) {
    ledState = !ledState;   // Toggle LED
    digitalWrite(LED_PIN, ledState ? HIGH : LOW);
    
    // Save to EEPROM
    writeEEPROM(0, ledState ? 1 : 0);
    
    Serial.print("Saved: LED ");
    Serial.println(ledState ? "on" : "off");
    
    delay(200);
  }
  
  lastButtonState = buttonState;   // For edge detection
  delay(50);   // Debounce
}

void writeEEPROM(int address, byte data) {   // I2C write one byte
  Wire.beginTransmission(EEPROM_ADDR);
  Wire.write(address >> 8);
  Wire.write(address & 0xFF);
  Wire.write(data);
  Wire.endTransmission();
  delay(5);
}

byte readEEPROM(int address) {   // I2C read one byte
  byte data = 0;
  Wire.beginTransmission(EEPROM_ADDR);
  Wire.write(address >> 8);
  Wire.write(address & 0xFF);
  Wire.endTransmission();
  Wire.requestFrom(EEPROM_ADDR, 1);
  if (Wire.available()) {
    data = Wire.read();
  }
  return data;
}

Program notes

Overall idea: In setup() read one byte from EEPROM address 0; if 1 then ledState=true and LED on, else off. In loop() detect button edge (HIGH→LOW), toggle ledState and writeEEPROM(0, ledState?1:0); on next power-up readEEPROM(0) restores. Review L28 I2C EEPROM read/write.

5. Hands-on

1. After entering the code, click Verify (✓) to compile
2. Click Upload (→) to upload to the board
3. Test:
   • Press button: LED state changes and is saved to EEPROM
   • Power off and on: LED restores to last state
4. Try yourself: save more settings (e.g. brightness, color)

Expected result: After power cycle, LED restores to the last saved state.

Proceed to Lesson 44.

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