By wathcing this video, you can understand PID in just 4 minutes. More explanation is given below on this website.
There are four different types of controllers and these are P, PI, PD and PID explanined below.
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard which opererate in a full duplex mode. Devices communicate in master or slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select lines with the chip select.
Introduction to I2C
An Inter-IC bus is often used to communicate across circuit-board distances. Here's a primer on the protocol.
At the low end of the spectrum of communication options for "inside the box" communication is I2C ("eye-squared-see"). The name I2C is shorthand for a standard Inter-IC (integrated circuit) bus.
I2C provides good support for communication with various slow, on-board peripheral devices that are accessed intermittently, while being extremely modest in its hardware resource needs. It is a simple, low-bandwidth, short-distance protocol. Most available I2C devices operate at speeds up to 400Kbps, with some venturing up into the low megahertz range. I2C is easy to use to link multiple devices together since it has a built-in addressing scheme.
What is the UART?
The UART, or Universal Asynchronous Receiver / Transmitter, is a feature of your microcontroller useful for communicating serial data (text, numbers, etc.) to your PC. The device changes incoming parallel information (within the microcontroller/PC) to serial data which can be sent on a communication line. Adding UART functionality is extremely useful for robotics. With the UART, you can add an LCD, bootloading, bluetooth wireless, make a datalogger, debug code, test sensors, and much more!
Understanding the UART could be complicated, so I filtered out the useless information and present to you only the useful need-to-know details in an easy to understand way . . .