The 555 Timer is a very cheap, popular and useful precision timing device that can act as either a simple timer to generate single pulses or long time delays, or as a relaxation oscillator producing stabilized waveforms of varying duty cycles from 50 to 100%. The 555 timer chip is extremely robust and stable 8-pin device that can be operated either as a very accurate Monostable, Bistable or Astable Multivibrator to produce a variety of applications such as one-shot or delay timers, pulse generation, LED and lamp flashers, alarms and tone generation, logic clocks, frequency division, power supplies and converters etc, in fact any circuit that requires some form of time control as the list is endless.
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.
Radio-controlled cars, boats, airplanes, etc use servos to control steering and other functions. The interface is well defined and the servos are quite affordable, so they are also used for robotics and other clever purposes. The servo positions itself based on the width of positive pulses fed to it. The rate at which pulses are sent to the servo is relatively unimportant(40 per second seems pretty typical).A servo motor has an output shaft that can be positioned by an encoded control signal. The motor drives the angular position of the controlled device.
Servo motors have three wires: