Real-world Feedback/Control Systems

1. Human body in relation to hunger
The human body is constantly monitoring its current state of hunger by noting different levels of hormones throughout the blood.  Put simply, when glucose levels drop, the body signals that it is requires food and consumes food until the glucose levels peak to optimal levels.  The sensing mechanism would be the pancreas, the actuation mechanism would most likely be the hypothalamus which is the main organ that monitors the majority of hormones in the body, and the control computation would be the hypothalamus responding to the state of the pancreas.  This system generally works well since glucose  levels are essential for energy and bodily functions.  However, there is a delay in the system.  Food must be broken down to a certain extent to be converted to glucose before it can be absorbed by the body. Therefore, the delay in determining how much food needs to be consumed before glucose levels are at sufficient levels may cause people to overeat.

2. GPS system
GPS systems in the phone rely on the phone's ability to communicate with satellites to monitor its position and determine how it can reach its destination.  There is a constant feedback loop between the phone sensing its current position and its needed route.  The sensing mechanism would be the GPS locator on the phone that determines its location.  The actuation mechanism would be the actual person moving in the physical world and following the directions of the system while the control computation would be the algorithms within the program that determine which route needs to be taken.  These types of systems can be reliable and are incredibly useful.  However, sometimes the routes the program chooses is not always the most efficient since it doesn't always take stopping at streets or speed limits into consideration.  There may also be some roads that are undesirable due to safety or time issues.

3. Thermostat
The thermostat is the most common type of feedback and control systems.  It relies on the sensing mechanism of the temperature sensitive pins which bend depending on the temperature.  The actuation mechanism would be the magnets that change the system to be either on or off while the control computation system would be the chemistry in the strip that allow it to bend at such sensitive measures of temperature and mechanisms that turn the system on or off depending on the state of the bimetal strip.

4. Fluxx
Fluxx is a program on computers that changes the tint of the screen depending on the time of day.  Blue light is a problem in many electronics because it can affect users ability to sleep at night and can strain their eyes during the day.  Therefore, later at night, the program triggers the screen to show more pink or yellow to contrast with the blue light and prevent users from suffering from affected sleep cycles.  The program asks for the user's zipcode to determine its position in the world and adjusts the screen depending on what time it is at that location.  The sensing mechanism would be the program's understanding of what time it is at the location.  The actuation mechanism would be the change in color on the screen while the control computation would be the program's algorithms to determine how blue, pink, and yellow the screen should be.  The system in general works well since it also provides users with the ability to change how bright, pink or yellow the screen should be.  However, sometimes the screen changes too abruptly between colors when it should be a more gradual fade.