If you study control theory you will encounter so-called block diagrams, which are schematic representations of control systems and help one to understand how they work. Below is the block diagram for a cruise control system.
Vin is the desired speed, set by the driver.
Vout is the actual speed on the speedometer.
The pale blue device calculates the error: e = Vin - Vout
The processor represents the engine and braking system.
Action of the controller:
- if e > 0, then accelerate
- if e < 0, then decelerate