IGCSE ICT

Control

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

The syllabus says you must:

Today’s objectives:

Understand the role of computers and sensors in control systems

Know the hardware required by a variety of control systems

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 syste

ms Programmable

microwave ovens

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

How Can Computers Control Things? A computer control system, like any

system, is made up of three parts:

OUTPUT: The computer turns on or off output devices

called actuators.

Sen

sors

Act

uato

rs

Processing…

The computer processes the input data by following a set of

instructions

INPUT:

Sensors feed data into the computer.

An analogy

Think about how a human controls a car when he/she is driving:

The person :1 .looks ahead at the road to see what is

approaching (INPUT) 2. thinks about what he/she has seen

(PROCESSING) 3. 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.

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 analogu

- - e to digital convertor.

Input: Hardware required

Making Decisions (The Pr ocess)

The steps followed by the computer in a control system are just about the sam

e for all systems...Read in the data from the sensorsCheck the data against a range of

preset values If necessary, turn on/off one or more o

f the actuators Go back to step 1

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 realworld.

Automatic washing machines

Sensors:Pressure (switch & door closed)

Water level/pressure

TemperatureDrum speedBalance

Actuators Motor Pump Heater LED Buzzer/bell

Automatic cookers

Sensors:Pressure (switch)TemperaturePressure (weight)

Actuators:LightHeaterBell/buzzerLED display

Central heating controllers

Sensors:TemperaturePressure (touchpad/switch)

Actuators:PumpMotorHeaterCooling UnitLED display

Burglar alarms

Sensors:Motion (PIR)LightPressureContactGlass breakSmokeHeat

Actuators:SirenLightMotor (automatic door & window locks)

Video recorders / players

Sensors:Pressure (switch) Infra red (tape/DVD in?)TrackMovement

Actuators:MotorLEDBuzzer

Microwave ovens

Sensors:TemperaturePressure (switch)

Actuators:MotorBuzzer/bellLightHeater

Computer controlled greenhouse

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

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

ActuatorsLights to illuminate the plants if it gets to

o 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

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 lightsGo back to step 1 and repeat

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

Water pump:

Read data in from moisture sensorCheck 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

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 .

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 t

hey can control a system without stopping, all day, every day

Computers don’t need to be paid . To buy and install a computeris

ed control system can be very ex - pensive, but, in the long term, m

oney is saved by not having to e mployee staff to do the work

Why use computers to control things:

Computers can operate i n conditions that would b e very hazardous to hum

an health, e.g. nuclear p ower stations, chemical f

- actories, paint sprayingareas

Computers can control s ystems far more accurat

ely, and respond to chan ges far more quickly tha

n a human could

Today’s assignment:

Your assignment for today is to make sure your notes are complete!

Go to bbc.co.uk/bitesizeComplete the Activity and the TestAdd any notes that you need to

Homework