Can I write to an I2C EEPROM with an arduino if it is powered by a different circuit?
As long as:


The ground of the Arduino and the AT24C16A are tied together.
The GND connection would dictate a 3-pin connector. (Or a three wire connection from Arduino to AT24C16A assembly).
The Arduino voltage swings are compatible with the EEPROM levels.
The Arduino software generates correct protocol for the I2C interface.
The software generates the correct SCL frequency of the AT24C16A.


You should be able to make it work just fine.