Serial Peripheral Interface (SPI)
Contributors:
MikeGrusin
MikeGrusin 
Introduction
Serial Peripheral Interface (SPI) is an interface bus commonly used to send data between microcontrollers and small peripherals such as shift registers, sensors, and SD cards. It uses separate clock and data lines, along with a select line to choose the device you wish to talk to.
Suggested Reading
Stuff that would be helpful to know before reading this tutorial:
Serial Communication
Asynchronous serial communication concepts: packets, signal levels, baud rates, UARTs and more!
Binary
Binary is the numeral system of electronics and programming...so it must be important to learn. But, what is binary? How does it translate to other numeral systems like decimal?