Topic 7—Control (14 hours)

JSR Note: Good to do a full overview birds eye view of Topic 7 in class # 1, and then go back to.

7.1 Control (14 hours)


control system is a device, or system of devices, that manages, directs or regulates the behavior of other devices or systems and/or itself. This can be as simple as a remote controlled toy car, all the way up to extremely complex industrial control systems in manufacturing plants.

Often, an important part of the control system is feedback from the controlled device - these are called closed loop control systems, and utilize sensors for supplying the feedback; for example a rivet machine on a car assembly line that gives feedback about the resistance encountered. Systems with no feedback from the controlled device are called open loop control systems; for example the speed control of a simple remote control car that doesn't sense it's about to crash into a wall.


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Simple diagram of a closed loop control system

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One of a myriad of industrial control systems ("Amerongen Hydrocentrale") used in manufacturing.


Control systems are generally described as being in one of three categories:


--- Centralized control systems --- (This is Assessment Statements 7.1.1 - 7.1.6)


Discuss a range of control systems.


Teaching Note:

A variety of control systems should be examined such as automatic doors, heating systems, taxi meters, elevators, washing machines, process control, device drivers, domestic robots, GPS systems, traffic lights and other common devices.

Technical knowledge of specific systems is not expected but students should be able to analyze a specified system.

AIM 9 Develop an appreciation of the possibilities for control systems with developments in computer systems.


With each of the examples below, you can imagine that in terms of IT, since here we are talking about centralized control systems, there is one central processor/microprocessing chip that handles everything.

Washing machines

General process: After you fill the tub with clothes, the machine fills the tub with water, and then stirs the clothes around using an agitator. Then, 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.

Washing Machine
By david007 sxuLicense



Washing Machine Parts
By Mrcnrmnwsk - Own w
ork, Public Domain


Timer Dial and Other Buttons
By Belchers Albert - Own work, CC BY-SA 3.0

- to begin, the user turns a big round dial to the desired routine and time

- when a start button is pressed the dial starts turning very, very slowly (due to a gearing down mechanism),

- as strips of various metal contacts on the dial pass by the main control contact, one of six or so cycles begins (like water in, or water out), with the completion of the given circuit

- the length of the various contact strips on the dial is what determines the duration of the various cycles - so this is an example of an open loop system

- there are switches for determine if hot or cold water is to be used, and a closed loop system of thermometer and microprocessor to keep the temperature at what was set initially

- and a water level sensor (so a closed loop system) which uses pressure to detect the water level in the tub, which is air tight when the door is closed. Or a weight sensor, since both clothes and water contribute to the overall weight being worked with.

  ---> Degree of local centralizedized control vs. more widely spread centralized control
Generally just within each washing machine.

Automatic Doors

(Like the Math Quad automatic doors just outside room 3-120)

- Either an infrared or microwave signal is sent from the main sensor down from the front middle of the door

- if that sensor receives positive feedback, in the form of the beam bouncing back at a certain level (so as not triggered by a mosquito), it is assumed a person is there, and a signal is sent to the processing unit

- the processing unit will then either open the door if it is closed, using two motors, or leave the doors open

- when the main sensor signal no longer is receiving beams bouncing back, it is assumed no one is waiting for the doors to be or remain open

- so then, control is shifted to another pair of photocell sensors to check to see if there is anyone in-between the two doors; alternatively touch sensors on the doors are (fortunately, for cats) used

- and if not, a signal is sent to the processor to close the doors,

- and the processor sends a signal to the the motors to close the doors

  ---> Degree of local centralized control vs. more widely spread centralized control:
Generally just within one door, though there could be more coordinated cenralized control when there are a series of doors one after the other, and the opening of one implies the other will soon need to open.

lh6.googleusercontent.com slidingdoorpic02.jpg



- Generally motors move an elevator up and down through a shaft based on requests received to go up or down from and to certain floors

- a up or down button pressed at a certain floor send that request to the processor

- the main processor then determines the optimal elevator (assuming more than one) to look after than request, based on both how close it is to that floor, and if it is currently in motion, direction it is going, and possibly also the current load weight

- the main processor knows where each elevator cab is through information sent to it from sensors in the cabs that read a series of holes in a long magnetic tape along the shaft

- the main processor, upon determination of the best cab for the request, sends the appropriate up/down signals to the appropriate elevator cab motor controlling it's suspension cables

- using feedback from the magnetic sensors, the cab will slow down gradually as it reaches a certain point, and stop at the desired floor

- the doors then open, remain open for a certain amount of time, and then automatically start to close

- if a person is still in-between the doors, an infrared and/or mechanical touch sensing devices within the doors will sense this, and trigger opening the doors again

- a button is pressed for the desired floor, this signal is sent to the main processor, and appropriate commands are then sent to the motors of that elevator cab

 ---> Degree of local centralized control vs. more widely spread centralized control: Each elevator can look after it's own, though take input from the others it is beside, or in a multi-elevator system, it makes sense to have more widely cast centralized control for the determination of which elevator is assigned to which job.

HowStuffWorks "How Elevators Work"

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(Mainly non-IT control system parts of an elevator)                     Elevator "Lifts" By Chris McKenna (Thryduulf), CC BY-SA 4.0

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 a microprocessor to request a walk sign

- the microprocessor then determines the appropriate time to wait to trigger the signal to change, based on the other traffic lights at that corer

- when the time has come, other lights are changed to amber and then red, and the walk sign is changed to go

Wikimedia CPT-FSM-FSA-Traffic.svg

By Pluke, Creative Commons CC0 1.0

Automatic traffic lights can use underground electrical wire to induce an electromagnetic field (an inductive loop detector) which will detect any presence of metal, i.e. a car, and send a signal to a processor to change the light to green.

Great video with several technologies for traffic lights control.

 ---> Degree of local central control vs. more widely spread centralized control
Can be an individual traffic light looking after itself, or more likely a system which is controlled in a centralized more widely, as with synchronized lights that turn green one after the other



The Global Positioning System (GPS)

- The US government's NASTAR GPS system that we all use consists primarily of thirty satellites which circle the globe at a fairly low orbit of 20,000 km, making two complete rotations every day.

- each satellite sends off microwave signals which our GPS receivers can receive

- these signals include information about the exact time the signal was sent, and its location.

- with this information, a distance of each satellite from the receiver can be determined

- and with at least three distances of three different satellites received, using the process of trilateration, an exact location of the receiver can be determined (it's basically the only place on earth these three distances could simultaneously intersect - and with a fourth, altitude can also be taken into consideration).

Great video explaining how GPS works

 ---> Degree of local central control vs. more widely spread centralized control
Centeralized control of all satallites from one "command center".

tctechcrunch2011 gps-image.jpg


Control Systems Mentioned In the Syllabus

Automatic Doors

General Description Sensor & Senson's Role Microprocessor's Role

(See above, also.) Basically, the whole process boils down to the optic/motion sensor. The sensors are mounted over and integrated within the door slides. The sensors use either infrared or microwave technology to observe motion. As the sensors detect the motion, then the door can be opened.

The optical or motion sensor is wired to an electrified main drive train that controls a clutch mechanism which opens up the door.

To report to the microprocessor whenever an object that is likely a person is within the set range of the sensor.

These sensors are pretty unintelligent: there is something there or not. But they may require a certain size to trigger them, so a mouse, for example would not.

To determine the various states ("particularly person approaching" or "no person approaching"), and send signals to open and close the doors accordingly.

Determination of whether to keep opening, or start closing (for example in the middle of a close operation, start opening again if an arm is still there.)

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Automatic doors

Alternatively, a weight sensor can be used to trigger the opening of the doors; if a person was standing in front of the door, then it would sense the change in weight, and the door would open.

The use of a weight sensor has an advantages of having a clearer measurement and has a less advanced level of technological sophistication and thus potential repair. With motion/optical sensors, even a change in air flow could potentially trigger the opening of the doors.

The use of weight sensor has clear disadvantage too. The area of detection is not as flexible as the one by motion detector, which can simply increase or decrease the detective range by putting less or more micro/infrared waves. Furthermore, the motion detector is much more durable, as the sensors are not the ones which receive the influence of the pressure directly.

Other alternatives (present or future) include:

Voice activation, laser, motion, like with Kinect, retina scanner, camera, the proximity of a key or card (as seen with modern cars' keys which unlock the car as the owner approaches).


Heating and Cooling Systems

General Description Sensor & Senson's Role Microprocessor's Role

An individual sensor keeps track of the temperature and adjusts the level of heating accordingly.

Or an array of sensors throughout the building send data back to a centralized microprocessor/server, and it controls the various heating or cooling systems.

The sensor senses the temperature in the room and reports it continually to the microprocessor.

In terms of physically how this is sensed: thermo-couples can sense changes in temperature to very small degrees.

Or, more conventionally, the sensor has something that expands and contracts with change in temperature.

And there are a variety of other teamperature sensing devices/techniques.

When the temperature reading in the room rises above a certain level, the heating/cooling unit is either turned down or turned off, and when the temperature reading falls below a certain level, the heating/cooling is turned up or turned on.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Heating Systems

An interesting thing is to note that a digital sensor is actually not as sensitive as an analog one.

But a microprocessor allows a lot more flexibility in how the temperature is regulated. For example, the user can make a schedule which sets varying target temperatures - warmer during the day and cooler during the night.

An improvement could be adding the control possibilities to the sensor itself, giving it a degree of autonomy. A "smart" sensor unit.


Taxi Meter

General Description Sensor & Senson's Role Microprocessor's Role

Both distance and waiting time needs to be tracked. A sensor is attached to the cab and every time the cab travels a certain distance, this sensor sends electric pulses to the meter. There is a timer in the meter that sends out a pulse whenever a certain amount of time has passed while stationary.

When in slow, or stop-and-go traffic, the meter will use a combination of distance and time data according to a certain algorithm.

One sensor passes the data necessary for distance calculations, and one sensor passes data about wait time to the microprocessor.

Distance is measured through the rotation of the wheels, as the encoders of a robot car work, so the sensor senses each rotation of the tire by proximity of a magnet, or laser with a time delay mechanism.

The microprocessor takes in the various inputs, both distance and wait time inputs and other selections made by the driver (like midnight to dawn extra charge, or bridge toll), and continually calculates and displays the fare on the meter.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Taxis

What are alternative ways of sensing input?

A motion sensor could be used to see how much of the time is spent traveling and how much is spent waiting. The amount of gas used by the car could be measured so fares accurately represent how much gas costs for the trip.



General Description Sensor & Senson's Role Microprocessor's Role

(See above also.)

Elevators are raised and lowered through either hydraulic presses or a system of ropes/pullies and counter-weights.

Technologies of the control system:

  • Control mechanisms to dictate where you are going (buttons and then through electric signals to either the valve or the control system)
  • Safety devices (phones, speakers, cameras will have various audio-visual sensors which relay to the microprocessor)
  • Different access methods to certain floors via secure cards or keys.
  • Weight sensors for overload.
  • Door senses pressure if closing on someone.
  • For certain kinds of elevators, it is entirely encoders which are responsible for the calculation of where to stop, and also for speed and acceleration; via a "closed PID loop".

The microprocessor controls opening and closing of doors in various normal operations and safety situations.

And the microprocessor may run sophisticated algorithms to determine the best up/down stop/start sequence during busy traffic times, and may even include data from other parallel elevators in the same building.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Elevators

"Smart" up/down stop/start algorithms will lead to much more efficient transport of passengers, particularly in multiple-elevator systems and during high traffic times.


Washing Machines

General Description Sensor & Senson's Role Microprocessor's Role

(See above, also.)

The control system of washer usually resides in the control panel or the timer of the machine. The user usually inputs the temperature, length, and intensity of the washing-cycle and the timer/control board takes this information and run the cycle.

Temperature (thermometer)
⁃ this is the only way to measure temperature

Water level (the option of a pressure switch)
⁃ this work by having the drum of the washing machine air tight, so that the air pressure inside the drum increases when water is added. Once the pressure reaches a specific point, the water valve is closed.

"Spin-out-of-balance" (displacement sensor)
⁃ measures how much the drum moves when it spins. obviously the drum needs to move a little when there is an uneven load, but when the drum spins irregularly to a point where its displacement is greater than normal, the
sensor gives of a warning message

- drum speed sensor...
- Water main failure (FloodStop) sensor...
- Door closed sensor...

The microprocessor has two functions:
⁃ 1) Taking in the values that the user gives and running a cycle with those values
⁃ i.e. running a cycle at 100º C, delicate, slow rotation...
⁃ 2) Making sure that all the sensor inputs (outlined above) are what they should be; if they aren't then the machine should report an error or try to fix it
⁃ i.e. if a cycle should be running at 100º but is at 90º, then the machine senses this and tries to correct it.

Other functions of the microprocessor:

- Control of heating the water to a specific temperature.

- Control of spinning speed.

- Monitoring weight, possibly via a simple Newton meter (a spring).

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Washing Machines

Digital sensing of the various inputs can increase the efficiency of the wash and flexibility of the kinds of cycles which can be run. In older models, there were a limited number of standard cycles, which did not take into account real load weights, for example.

Some sort of biological sensor to determine when the load is clean, based on the amount of remaining bacteria etc. in the water.


Process Control

General Description Sensor & Senson's Role Microprocessor's Role
By this, any multi-step process could seen as process control, and so the situation of sensors on an assembly line at a factory controlling things. Various sensors sensing various things. Think of a car assembly line, and things to be sensed such as where parts are, and when rivets have been successfully riveted, and the temperature of various machinery and robots. Tons, and tons of things to be sensed, and controlled through a heirarchical distributed control system, both for efficiency and safety reasons.

To interpret all the various sensor input information, and send back control instructions to the various machines/robots based on that data.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Process Control

Increased autonomy handed over to the various machines or robots.


Device Drivers

General Description Sensor & Senson's Role Microprocessor's Role
This usage of device drivers probably means peripherals connected to a computer, say for example: a joystick or mouse.

Mouse Example - two types:

Optical mouse sensor senses: acts like a dumb camera, and when it moves, communicates this to the computer.

Mouse ball sensor - moving ball rotates the horizontal and vertical rollers.

Microprocessor is actually in the computer, but it takes in the data from the mouse via the sensor. The processing is done by the CPU in conjunction with the driver software

In the mouse example, to interpret the signals given from the sensor, via working with the specific mouse (software) driver, and then pass on the desired cursor movement etc. to the application being used.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Device Drivers

In the mouse example, solve the issue of optical mice dysfunction on certain shiny surfaces.


Domestic Robots

General Description Sensor & Senson's Role Microprocessor's Role
Automated roaming vacuum cleaners, such as the Roomba track around a floor according to a variety of algorithms, and when they bump into a wall or furniture, they change direction and keep on cleaning. The main sensor is the touch sensor about the circumference of the machine; it's role is to feedback to the microprocessor when it has hit the wall, or some other obstacle.

The processor, in a basic one of these machines, simply controls the time of the clean and determines when an obstacle has been struck, and which direction to then try going.

In a potentially more sophisticated machine, one way or the other, information about the room to be cleaned is taken into consideration in the development of an ideal series of cleaning forays.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Domestic Robots

There theoretically could be sensors to sense the "cleanliness" of the floor over which the robot currently is. This could be done through the sensing of physical particles being taken in, or through smell.

Poor algorithms can result in both a waste of time and energy, and parts of a floor being missed - so work is still needed to improve cleaning algorithms.


GPS System

General Description Sensor & Senson's Role Microprocessor's Role

(See above, also.)

Here's another good GPS video, with another good description of trilateration.

You'll recall from above that it's all based on trilateration of the distances of three satellites from the ground position.

Ground Control Stations (could be our phone's GPS receiver): Sensors continually receive location information from each satellite.

The Satellites Themselves: Somehow they must precisely sense their position over the earth, to be reported to their microprocessors in case corrective positioning must be taken.

Ground Control Stations: the microprocessors monitor various important processes going on in each satellite which maintain its stable orbit, and also potentially instruct corrective measures on board the satellite when errors or problems occur.

The Satellites Themselves: the microprocessors control all of the activities of the satellite, including the important transmission of "beams" down to earth, where GPS units receive them.

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for GPS Systems

New geo-positon-using apps are being developed every day, since the smart phones which use them move with their owner, and can therefore report back things such as the nearest pizza restaurant or police station.


Traffic Lights

General Description Sensor & Senson's Role Microprocessor's Role

(See above, also.)

  1. Inductive loops: A groove is cut on an asphalt road, electric circuits are placed and covered. Whenever cars pass on, those electric circuits sends signal to the traffic light connected to them that the traffic light can sensor how many cars are coming or waiting.

  2. Detectors: Detectors mounted on poles beside roads sensor cars. This way is more efficient then inductive loops. It takes less money to install, and also able to send real-life photos as well that inductive loop cannot do.
The sensor reports back continually to the microprocessor when a vehicle is approaching (either through motion detection or weight detection).

The microprocessor takes in the sensed motion or electromagnetic signal, and initiates the change in the traffic light's color, either immediately, or upon consideration of traffic going the other way and/or the amount of time since the light last changed color. Other inputs can be taken into consideration, such as if a tram is coming one direction or another (in Prague, at least, trams trump cars in almost all traffic interchange situations; the way they are going will be a green light - refer to the video linked above for more on this.)

Improvements Over Past or Alternative Systems      &      Possibilities for the Future      for Traffic Regulation

Past: A fixed traffic light system, which does not require/use sensor systems at all; the traffic light rotates to green and red for certain time period.

Future: Infrared: Cars emit infrared that are recognized by devices can communicate with traffic lights. However, one disadvantage is if this is not part of the original car, then people have to buy devices.

Radio Frequency: Input would be radio wave. This could be used without extra installation such as infrared since most cars have radio function. However, the problem is that Radio waves are not always recognizable, especially when the car windows are covered with coating.

Card sensor: Input would be information in cards such as bar code or QR code. Traffic lights sensor card within cars and analyze information. This could require less money than Inductive Loops method.

But all of this will soon be replaced by a distributed control system of all vehicles, autonomously driven, but continually supervised also.


Interesting Current Control Systems Under Development

Control System General Description Microprocessor's Role Sensor & Sensor's Role

Improvements Over Past

& Possibilities for the Future

GPS Personal Tracker Either embedded under the skin, or worn as a watch or bracelet etc., it reports back to a parent or parole officer where a person, or indeed a dog or cat is.

Tracked Device: Receive the GPS information and do the calculations required to determine geo location.

Tracking Device: Interpret the signal transmitted by the bracelet etc., and determine the exact location.

And possibly alert the user when the location of the person/animal being tracked is out of the range of the desired/allowed location.

Tracked Device: Sense the signals from the three satellites necessary for the calculation.

Tracking Device: Sense the transmitted signal from the bracelet etc.

Great safety addition for parents and pet owners. Great benefits for parole officers and other law enforcement officials.

But there are ethical implications.

Auto-driving Cars Cars sense their environment, including the free road ahead and any obstacles which could cause an accident, and with this information drive the car, only handing back control to the human operator in case of an emergency "exception" the driving algorithm was not programmed to handle. Make a myriad of constant calculations, which basically re-construct the scene the car is driving through in 3D, and then with this information, determine the most efficient and safest way to proceed, and then to send the appropriate driving instructions to the various devices such as gas pedal and breaks and blinkers. Sense all the objects around the car, from the center median of the road, to pedestrians, to other cars, to road hazards such as hedgehogs.

You can safely text while driving.

But driving does become a lot less exciting. Still, it's the vast improvements in safety which will drive this development very quickly.

Drone Parcel Delivery On-line orders initiate merchandise in a warehouse being taken (either manually or robotically) to an aerial drone launch pad. The drone then flies to the destination and drops off the parcel. Likely these destinations will be shared neighborhood landing and storage areas, analogous to rural group mailboxes. A code will release the appropriate merchandise to the receiver, as from a vending machine.

Drone: Using GPS, information from air traffic control, and current environmental conditions information, the microprocessor will determine the best, safest, most efficient route to the destination, and control the routers of the drone.

Neighborhood Dispenser: Taking in a security code, it will match it up with an order and dispense the package.

Drone: Sensors will take in GPS, air traffic control, and environmental information. They will also continually evaluate local weather conditions, and the orientation of the drone, so that it can be leveled when needed.

Neighborhood Dispenser: Takes in the code, and/or a thumb print or some other security key.

No need to travel relatively large distances to stores. Yet a lot quicker delivery than relying on a network of delivery trucks and drivers.

But will likely never happen; who wants a bunch of drones constantly overhead?

Control of Exoskeleton

By joystick: A strong exoskeleton is controlled by a non-disabled person to do various super-human feats, such as lifting/carrying heavy loads, and defeating vile villains from the outer reaches of our galaxy.

By brain waves: A quadriplegic person is able to walk and do other things with their four limbs and hands and feet by controlling the exoskeleton with brain waves. The first kick of the 2014 FIFA World Cup in Rio is to be done with this kind of control.

By joystick: The processor translates various movements of the joystick, and presses of buttons into actions by the various robotic limbs and digits.

By brain waves: The processor translates various brainwave signals into actions by the various robotic limbs and digits.

By joystick: The various movements of the joystick and preses of buttons are sensed either through pressure or through closing of electrical circuits.

By brain waves: The sensor detects certain levels of electrical activity, and certain distinctive patterns of electrical activity of the brain that can be confidently and consistently produced by the user, after a bit of training and practice.

By joystick: Combines the flexibility and convenience of the human body with the strength of large, awkward, hard to control machines.

By brain waves: There could be nothing more liberating for a person with no control of any body movement below their neck.


Other Great Examples:

- Auto car wash



Sample Question 1 - FORMER CURRICULUM (and not too applicable, but worth a look):

Outline an application that would make use of a touch screen for input of data. [2 marks]

Sample Question 2 - FORMER CURRICULUM (and not too applicable, but worth a look)

A car-park opens from 07:30 to 18:00 each day and functions as follows:

When a car is about to enter the car-park, a ticket is issued to the driver and the barrier is raised,
allowing the car to enter.

When the driver wishes to leave, he/she must insert the ticket into the pay-machine and pay the
amount displayed.

(a) Suggest how the pay-machine is able to automatically determine the time of
entry when calculating the cost of parking. [3 marks]