IGCSE ICT – Controlling Real-World Things | IGCSE ICT

Source: IGCSE ICT – Controlling Real-World Things | IGCSE ICT

How Can Computers Control Things?

A computer control system, like any system, is made up of three parts…

1. Input devices called sensors feed data into the computer
2. The computer then processes the input data (by following a set of instructions)
3. As a result of the processing, the computer can turn on or offoutput devices called actuators.

The best way to understand how a computer can control things is to think about how a person controls something…

For example, how does a human control a car when he/she is driving?

The person looks ahead at the road to see what is approaching, thinksabout what he/she has seen, then acts upon it (turns the steering wheel and/or presses the pedals).

In other words the person reacts to what is happening in the world around them.

Computer-controlled systems work in a similar way – the system detects what is happening in the world around it, processes this information, and then acts upon what it has detected.

Sensors

A normal PC has no way of knowing what is happening in the real world around it. It doesn’t know if it is light or dark, hot or cold, quiet or noisy. How do we know what is happening around us? We use our eyes, our ears, our mouth, our nose and our skin – our senses.

A normal PC has no senses, but we can give it some: We can connect sensors to it…

A sensor is a device that converts a real-world property (e.g. temperature) into data that a computer can process.

Examples of sensors and the properties they detect are…

Sensor	What it Detects
Temperature	Temperature
Light	Light / dark
Pressure	Pressure (e.g. someone standing on it)
Moisture	Dampness / dryness
Water-level	How full / empty a container is
Movement	Movement nearby
Proximity	How close / far something is
Switch or button	If something is touching / pressing it

Note: many sensors are analogue devices and so need to be connected to the computer using an analogue-to-digital convertor.

Actuators

A normal PC has no way of affecting what is happening around it. It can’t turn on the lights, or make the room hotter. How do we change what is happening around us? We use our muscles to move things, press things, lift things, etc. (and we can also make sound using our voice).

A normal PC has no muscles, but we can give it some. In fact we can give it the ability to do lots of things by connecting a range of actuatorsto it…

An actuator is a device, controlled by a computer, that can affect the real-world.

Examples of actuators, and what they can do are…

Actuator	What it Can Do
Light bulb or LED	Creates light
Heater	Increases temperature
Cooling Unit	Decreases temperature
Motor	Spins things around
Pump	Pushes water / air through pipes
Buzzer / Bell / Siren	Creates noise

Note: some of these devices require an analogue signal to operate them. This means that they need to be connected to the computer using a digital-to-analogue convertor.

Making Decisions (The Process)

The steps followed by the computer in a control system are just about the same for all systems…

1. Check the data from the sensors
2. If necessary, turn on/off one or more of the actuators
3. Go back to step 1

That’s it! Of course the details vary, but that is basically how things work.

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

If we look beyond our homes, we come across even more systems that operate automatically under the control of a computer…

• 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

Of course, car engines, factories and traffic lights were not always computer-controlled. Before microprocessors even existed, car engines ran, factories produced goods and traffic lights changed.

However using computers to manage these systems has brought many benefits…

Why Use Computers to Control Thing?

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
• 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

An Example Control System – An Automated Greenhouse

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

• 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
• 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

The process for this system would be…

1. Check light sensor
   • If it is dark, turn on the lights
   • If it is not dark, turn off the lights
2. Check temperature sensor
   • 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
3. Check the moisture sensor
   • If soil is too dry, turn on the water pump
   • If soil is too wet, turn off the water pump
4. Go back to step 1 and repeat

Note that 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.

 

Networks Topologies

The word topology means ‘arrangement’, so when we talk about the topology of a network, we mean how the different parts are arranged and connected together.

There are three common network topologies…

Bus Network

In this type of network, a long, central cable, the ‘bus’ is used to connect all of the computers together. Each computer has a short cable linking it to the ‘bus’.

A bus network…

• Is cheap to install (just one long cable)
• Can be quite slow since all computers share the same cable when communicating
• Will stop working if there is a break in the central bus cable.

Ring Network

In this type of network each computer is connected to a loop of cable, the ‘ring’. (If you took a bus network and connected the ends of the bus cable together, you would have a ring network.)

A ring network…

• Can cope with a break in the ring cable since all computers are still joined together (it is now a bus network)

Star Network

In this type of network every computer is connected to a central device. The device passes messages between computers.

At the centre of a star network you might use a hub (cheap, but slower) or a switch (more expensive, but faster).

A star network…

• Is quite expensive to install (you have to buy lots of cableand the central device)
• Is very fast since each computer has its own cable which it doesn’t need to share
• Can cope with a broken cable (only one computer will be affected)
• Will stop working if the central device breaks
• Is the most common network topology

Hybrid Network

A hybrid network is simply one that combines two or more of the above basic topologies.

E.g. A network that has several star networks linked together is a hybrid network

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