Interfacing with Arduino
As well as using straightforward digital inputs and outputs to connect electronics to an Arduino, the Arduino also supports three common standards for serial interfaces. These are I2C (pronounced “I squared C”), SPI, and UART (or TTL Serial).
Whereas digital and outputs are fine for connecting switches or LEDs with no intelligence, the serial interfaces to Arduino are often used to connect ICs or modules that might have their own microcontroller built-in. Serial communication is the norm when you need to send and receive more information than a single high or low. This includes some sensor chips that might send their readings as a stream of binary digits, or display modules that expect to be sent a stream of binary ...