Block diagram for cruise control

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.

V_in  is the desired speed, set by the driver.
V_out  is the actual speed on the speedometer.
The pale blue device calculates the error: e = V_in - V_out  
The processor represents the engine and braking system.

Action of the controller:

• if e > 0, then accelerate
• if e < 0, then decelerate