AT24C256 I2C EEPROM Memory Module - 256Kb (32KB) Non-Volatile Storage

Specifications

• Memory IC: AT24C256

• Memory Type: EEPROM (Non-Volatile)

• Storage Capacity: 256 Kilo-bits (32 KiloBytes / 32,768 x 8 bits)

• Communication Interface: I2C (SCL, SDA)

• Operating Voltage: 2.7V to 5.5V DC (3.3V and 5V Logic Compatible)

• I2C Clock Speed: 100 kHz (Standard Mode) / 400 kHz (Fast Mode)

• Write Endurance: 1,000,000 Write Cycles

• Data Retention: >100 Years

• Onboard Components: 10K Ohm I2C Pull-up Resistors

• Pinout: VCC, GND, SCL, SDA

• Board Dimensions: ~19mm x 11mm

Key Applications and Projects

• Weather Station Data Logging: Taking temperature and humidity readings every hour and saving the data points to the EEPROM so they are not lost if the station's battery temporarily dies.

• IoT Device Configuration: Storing user-inputted WiFi SSIDs, passwords, and API keys securely so the device can reboot and automatically reconnect to the network.

• Robotics Calibration: Saving complex PID tuning variables and servo "zero" positions so the robot doesn't have to be recalibrated every time you turn it on.

Unlock New Capabilities (Project Evolution) The Offline Black-Box Flight Recorder: SD card modules can suffer from file-system corruption if power is pulled mid-write during a drone crash. EEPROM does not use a file system; it stores raw bytes. Evolve your custom drone or RC plane! Wire this lightweight module to your flight controller. Write a script to continuously overwrite the EEPROM with the last 10 seconds of GPS coordinates, altitude, and pitch angles. If your drone crashes and the battery ejects, simply recover the board, plug it into a laptop, and dump the EEPROM to see exactly what happened in the moments before the crash!

Package includes:

• 1 x AT24C256 EEPROM Storage Module

• 1 x 4-Pin Straight Male Header (Unsoldered)

FREQUENTLY ASKED QUESTIONS (FAQ)

1. What exactly is EEPROM? EEPROM stands for Electrically Erasable Programmable Read-Only Memory. It is a type of non-volatile memory chip that retains its data even when power is completely removed from the circuit.

2. What does 256Kb mean in actual bytes? Memory chips are rated in "bits" (lowercase b). 256 Kilo-bits divided by 8 equals 32 KiloBytes (KB) of actual usable storage capacity.

3. What happens to the data if the power goes out? Absolutely nothing. Because it is non-volatile memory, the data is physically trapped in the silicon and will remain there safely until you overwrite it or erase it.

4. What voltage does this module operate on? The AT24C256 chip natively supports a wide operating voltage range, typically from 2.7V up to 5.5V DC, making it highly versatile.

5. Can I use this with a 3.3V microcontroller like an ESP32 or Raspberry Pi? Yes! Because it operates happily at 3.3V, you can wire VCC to 3.3V and connect the I2C lines directly to your ESP32 or Pi without needing a logic level shifter.

6. Does this module use I2C or SPI communication? This module utilizes the I2C (Inter-Integrated Circuit) protocol, requiring only the SCL (Clock) and SDA (Data) pins.

7. Do I need to add external pull-up resistors for the I2C lines? No. If you look closely at the board, there are two tiny black surface-mount resistors marked "103" (10K Ohms). These are onboard pull-up resistors for the SDA and SCL lines.

8. What is the default I2C address for this module? For the AT24C256, the default I2C address is usually 0x50.

9. Can I change the I2C address to use multiple modules on the same board? Unlike some larger EEPROM breakout boards, this specific minimalist 4-pin module does not break out the A0, A1, and A2 address pins. They are hardwired on the PCB. To use multiple of these specific 4-pin modules, you would need an I2C multiplexer (like the TCA9548A).

10. How many times can I write data to this memory? The chip is rated for approximately 1,000,000 write cycles per memory block.

11. Is there a limit to how many times I can READ the data? No. Reading data causes virtually zero wear on the silicon. You can read the data billions of times without degrading the chip.

12. How long will the memory hold its data? The AT24C256 is rated for a data retention lifespan of over 100 years.

13. Do I need to solder the header pins? Yes. The module ships with a loose 4-pin male header strip. You will need a soldering iron to attach it to the main PCB to plug it into a breadboard.

14. Can I store text or strings on this module? Yes, but EEPROM only understands raw bytes. To store a string of text (like a password), you simply convert the characters into their ASCII byte equivalents and store them in sequential memory addresses.

15. What Arduino library should I use? You can use the standard Arduino <Wire.h> library for basic I2C communication, but downloading a dedicated EEPROM library (like extEEPROM or AT24C256 from the Library Manager) makes writing and reading data much easier.

16. How fast is the I2C interface? The chip supports standard mode (100 kHz) and fast mode (400 kHz) I2C clock frequencies.

17. What is the hole in the middle of the board for? That is a mechanical mounting hole. It allows you to securely bolt the tiny module to your robot chassis or 3D-printed enclosure so it doesn't bounce around on its wires.

18. Why would I use this instead of an SD Card module? SD cards require significantly more power, use complex file systems that can easily corrupt if power is lost during a write, and require more pins (SPI). EEPROM is much simpler, vastly more reliable, and perfect for small amounts of critical data.

19. Does it matter which way the header pins are soldered? You can solder them sticking up from the component side or pointing down from the flat bottom side, depending on how you intend to mount it in your project. Pointing down is best for breadboard use.

20. What is "Page Writing"? The AT24C256 supports a 64-byte Page Write. This means instead of sending a slow write command for every single byte, you can load 64 bytes into a buffer and write them to the memory simultaneously, significantly speeding up data logging.