1. IGCSE ICT
Control

2. The syllabus says you must:
understand the use of control applications:
turtle graphics
control of lights, buzzers and motors
automatic washing machines
automatic cookers
central heating controllers
burglar alarms
video recorders / players
microwave ovens
computer controlled greenhouse

3. Today’s objectives:
Understand the role of computers and sensors in control systems
Know the hardware required by a variety of control systems

4. Where is Computer Control Used?
Many of the devices that we use in our everyday lives are controlled by small computers...
Washing machines
Air-conditioning systems
Programmable microwave ovens

5. Other uses of control applications:
Modern cars have engines, brakes, etc. that are managed and controlled by a computer
Most factory production lines are computer-controlled, manufacturing products with little or no human input
Traffic lights are switched on and off according to programs running on computers which manage traffic flow through cities

6. How Can Computers Control Things?
A computer control system, like any system, is made up of three parts:

7. The computer turns on or off output devices called actuators.
Processing…
Actuators
Sensors
INPUT:
Sensors feed data into the computer.
The computer processes the input data by following a set of instructions
OUTPUT:
The computer turns on or off output devices called actuators.

8. An analogy
Think about how a human controls a car when he/she is driving:
The person :
looks ahead at the road to see what is approaching (INPUT)
thinks about what he/she has seen (PROCESSING)
acts upon it (OUTPUT: turns the steering wheel and/or presses the pedals).
In other words the person reacts to what is happening in the world around them.

9. Input: Hardware required
A computer can’t look around, so it needs to have sensors attached to it.
A sensor is a device that converts a real-world property (e.g. temperature) into data that a computer can process.
Because physical data can have an infinite range of values, most sensors are analogue devices and so need to be connected to the computer using an analogue-to-digital convertor.

10. Making Decisions (The Process)
The steps followed by the computer in a control system are just about the same for all systems...
Read in the data from the sensors
Check the data against a range of preset values
If necessary, turn on/off one or more of the actuators
Go back to step 1

11. Output: the Actuators
A normal PC has no way of affecting what is happening around it. It can’t turn a steering wheel or flick a switch.
We use our muscles to move things, press things, lift things, etc.
A computer has no muscles, but we can give it some: we can give it the ability to do lots of things by connecting a range of actuators to it…
An actuator is a device, controlled by a computer, that can affect the real-world.

12. Automatic washing machines
Sensors:
Pressure (switch & door closed)
Water level/pressure
Temperature
Drum speed
Balance
Actuators
Motor
Pump
Heater
LED
Buzzer/bell

13. Automatic cookers Sensors: Pressure (switch) Temperature
Pressure (weight)
Actuators:
Light
Heater
Bell/buzzer
LED display
(Since weather is so complex, and the models are not (yet) accurate enough, often the weather forecast is wrong!)

14. Central heating controllers
Sensors:
Temperature
Pressure (touchpad/switch)
Actuators:
Pump
Motor
Heater
Cooling Unit
LED display

15. Burglar alarms Sensors: Motion (PIR) Light Pressure Contact
Glass break
Smoke
Heat
Actuators:
Siren
Light
Motor (automatic door & window locks)

16. Video recorders / players
Sensors:
Pressure (switch)
Infra red (tape/DVD in?)
Track
Movement
Actuators:
Motor
LED
Buzzer

17. Microwave ovens Sensors: Temperature Pressure (switch) Actuators:
Motor
Buzzer/bell
Light
Heater

18. Computer controlled greenhouse
A computer-controlled greenhouse might have a number of sensors and actuators:

19. Sensors A light sensor to detect how much light the plants are getting
A temperature sensor to see how cold/hot the greenhouse is
A moisture sensor to se how wet/dry the soil is

20. Actuators Lights to illuminate the plants if it gets too dark
A heater to warm up the greenhouse if it gets too cold
A water pump for the watering system
A motor to open the window if it gets too warm inside

21. How would the processes work?
Light Sensor:
Read data in from light sensor
Check data against pre-set/permitted values
If it is dark, turn on the lights
If it is not dark, turn off the lights
Go back to step 1 and repeat

22. Heaters & Windows: Read data in from temperature sensor
Check data against pre-set/permitted range of values
If it is too cold, turn on heater AND use motor to close window
If it is too warm, turn off heater AND use motor to open window
Go back to step 1 and repeat

23. Water pump: Read data in from moisture sensor
Check data against pre-set/permitted range of values
If soil is too dry, turn on the water pump
If soil is too wet, turn off the water pump
Go back to step 1 and repeat

24. Be careful:
if you have to describe a control process, never say that anything like: “the temperature sensor switches on the heater” This is totally wrong! Sensors cannot control anything - all they can do is pass data to the computer. The computer takes the actions and turns on/off the actuators.

25. Why use computers to control things:
It is often far better to have a system that is managed and controlled by a computer rather a human because...
Computers never need breaks - they can control a system without stopping, all day, every day
Computers don’t need to be paid. To buy and install a computerised control system can be very expensive, but, in the long-term, money is saved by not having to employee staff to do the work

26. Computers can operate in conditions that would be very hazardous to human health, e.g. nuclear power stations, chemical factories, paint-spraying areas
Computers can control systems far more accurately, and respond to changes far more quickly than a human could

27. Today’s assignment:
Your assignment for today is to make sure your notes are complete!

28. Homework Go to bbc.co.uk/bitesize Complete the Activity and the Test
Add any notes that you need to