Computer control

Computers are also used for controlling and monitoring tasks. Such computers are called as control systems.
Like any other computer, control systems are also made up of three parts:

  1. Input devices called sensors feed data into the computer.
  2. The computer then processes the input data (according to the program)
  3. As a result of the processing, the computer can turn on or off output devices called actuators.

How do we, human beings know what is happening around us?
We use our eyes, our ears, our mouth, our nose and our skin (our senses.)

But a computer 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, light, pressure etc.) into data that a computer can process.

Example for sensors are:

  • Temperature sensor
  • Pressure sensor
  • Humidity sensor
  • Light sensor
  • Sound sensor


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 actuators to it.
An actuator is a device, controlled by a computer, which can affect the real-world.
Some of the examples are – motor, pump, buzzer , heater etc.

Processing (decision making)

The steps followed by the computer in a control system are just about the same for all systems:
Check the data from the sensors.
If necessary, turn on/off one or more of the actuators.
Go back to step 1.

Advantages of using computer control

  1. Computers don't need breaks - they can work 24 hours 7 days without stopping
  2. 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.
  3. Computers can work in extreme conditions that human beings cannot. e.g. nuclear power stations, chemical factories, paint-spraying areas.
  4. Computers are more accurate than human beings.
  5. They respond more quickly than a human could.

Burglar alarm system

An automatic burglar alarm system works on the principle of IPO:

Input -> Process -> Output.

Let us see what is input – process – output?

  • Computer controlled and monitored system gathers information from the sensors.
  • A computer controlled burglar alarm system might have number of sensors
  • Movement sensors – detects movement within the range of the sensors.
  • Passive infra red sensors – detects something moving within the range of sensor
  • Pressure sensor - detect somebody enters a certain area​​

ADC ( Analogue to Digital Converter)

Computers are digital devices, hence only understand digital data. Whereas sensors are analogue devices and produce only analogue data.
So to make the computer able to understand the data sent by the sensors we need a converter called Analogue to Digital Converter.

DAC (Digital to Analogue Converter)

Sometimes computer will have to send instructions/commands to actuators.
We know that computers are digital devices and actuators are analogue devices. To make this communication possible we use a converter between the computer and actuators, called Digital to Analogue Converter (DAC)

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