7.1.1+Discuss+a+range+of+control+systems. 

Washing machines
After you fill the tub with clothes, the machine fills the tub with water, and then stirs the clothes around using an agitator.

After some time agitating, the washer drains the water and then spins the clothes to remove most of the water. Then, it refills, and agitates the clothes some more to rinse out the soap. Then it drains and spins again. This is basically what a washing machine does, but how it actually works is different.


 * Inside a washing machine: **

The cycle switch has the job of determining how long the different parts of the cycle last.

Inside the switch is a motor equipped with a gear reduction that makes the control dial turn very slowly. In the top half of the switch, there is a set of six contacts. These are actuated by the small pieces of metal in the plastic arm on the dial. As the dial spins, bumps on the dial raise and lower the six metal pieces, which close and open the contacts in the top half of the switch.

This bumpy plastic disk is really the software program that runs your washing machine. The length of the bumps determines how long each part of the cycle lasts, and the length of the space between bumps determines how long the machine pauses before moving on to its next task.

These switches control the speed of the motor and determine which of the hot/cold water supply will open during the wash and the rinse cycles. If hot is selected, only the hot water valve will open when the machine fills; if warm is selected, both will open; and if cold is selected, only the cold water valve will open.

The level sensor uses a pressure switch to detect the water level in the tub, which controls how high the tub fills with water. As the water rises air is compressed, causing an increase in pressure and affecting the sensor.

Automatic Doors
Automatic doors consist of a sensor, a processor and an automator. The sensor is often infrared and sends out infrared signals which then bounce off of objects. These signals can also be microwaves. The sensor then receives the signal and then sends a signal to the processing unit which then processes the information and sends it to the automator, in the form of two motors that cause the doors to open for a brief moment, and then close.

This is only the basis of the door. Below, it is possible to see that there are also photocells that make sure that the door does not close on people walking through. These sensors sense if there is someone in the way and sends a signal to the processor. If this signal is true, stating that there is somebody in the way, the doors will not close. The processor will then see whether the doors should open or close, based on the information that it has received from the sensors. If the infrared sensor senses a person, the processor will tell the motors to open the door. Then, if the the photocells do not sense a person in the way, the processor will send the signal to close the door again.

Elevators
A person will first press a floor button to call an elevator. The computer will receive this and send the best suited elevator to that floor, this is determined by not only the position of the elevators but also the direction of the elevators currently in use. The computer can ‘see’ where the elevator cab is in the shaft as the cab has magnetic sensors on its side that read a series of holes in a long magnetic tape along the shaft. The computer will send the cab to the floor with motors that control the movement of the elevator. The motor will control the movement of the elevator cab with suspensions cables. When the elevator reaches the floor the doors will only open when the cab reaches a certain point (read with the magnetic sensor), the cab door will also have a timer to ensure it does not stay open without a passenger pressing the close door button. The passenger will then press the button of which floor he/she wishes to go to. This is request is sent to the computer. The computer will then proceed to activate the motors pulling the elevator cab to the passengers desired floor. When the elevator is approaching the floor the computer (recognized with the magnetic sensors) tells the motors to slow down gradually until a full stop at the desired floor. When the floor is reached, the doors will open. || ||
 * In the most basic sense: an Elevator Control System consists of buttons on the floors of a building and within the elevator, a motor to move the elevator up and down, motorised doors, and a computer to control everything.

Traffic Lights
Pedestrian crossing often use traffic lights to ensure safety for both the drivers and the pedestrians. The pedestrian pushes a button which sends a signal to the microprocessor. This then waits for an appropriate time to trigger the signal to change with the use of other sensors.

Traffic lights use underground electrical wire to induce an electromagnetic field which will detect any presence of metal.

GPS
The Global Positioning System (GPS)

Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day.

If you know you are 10 miles from satellite A in the sky, you could be anywhere on the surface of a huge, imaginary sphere with a 10-mile radius. If you also know you are 15 miles from satellite B, you can overlap the first sphere with another, larger sphere. The spheres intersect in a perfect circle. If you know the distance to a third satellite, you get a third sphere, which intersects with this circle at two points. The Earth itself can act as a fourth sphere -- only one of the two possible points will actually be on the surface of the planet, so you can eliminate the one in space. Receivers generally look to four or more satellites, however, to improve accuracy and provide precise altitude information.