The ICT Lounge
 
Section 7.4:
Control Devices (Examples)
 
Computers can be used to control a range of devices through the use of sensors. Some of these devices include:
Key Concepts of this section:
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Understand how computers can control devices automatically.
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Know why computers are more effective at controlling devices than people.
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Be able to discuss different examples of devices that can be controlled by computers.
  • Security Lights
  • Burglar Alarms
  • Central Heating Controllers
  • Computer Controlled Greenhouses
  
  • Automatic Cookers
  • Automatic Washing Machines
  • Microwave Ovens
Controlling stuff using Computers
Key Words:
Sensor, Input, Process, Output.
The role of the sensor
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In section 7.3 we looked at how sensors could be used alongside computers to measure quantities (like temperature, light intensity etc) and then log changes in these quantities.

Sensors can also be used alongside computers to control different devices . The process goes like this:
Examples of Sensors
Temperature/Heat - Detect changes in temperature.
Light Sensor - Used to detect the brightness of light.
Sound Sensor - Detect the loudness of sound.
Humidity Sensor - Detect water in air.
Infra-red Sensor - Detect movement (Used in burglar alarms).
Load/Weight Sensor - Detect weight (Used in digital scales).
Proximity Sensor - Detect how near/far something is.
 
REMEMBER!
Most sensors are Analogue so we can only connect them to a computer using an Analogue to Digital Converter.

 
Input -
Sensor detects data in the environment around it
Process -
Data passed to a computer (microprocessor) inside the device which analyses it and decides what action to take. The computer sends instructions to the device telling it what to do.
Output -
The device would carry out the instructions.

Picture Example:

Advantages of using a computer to control devices rather than people
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Computers have certain advantages over people when it comes to controlling devices. For example:
Radioactive sites can be too dangerous
for people to work in.
 
Cheaper -
If a computer is monitoring and controlling applications, you do not need to employ people.
Higher Work Rate -
Computers can control applications all day, every day without getting tired or bored.
Safer -
Computers can work in conditions that would be too dangerous for people. Examples include chemical plants, radioactive sites and extremely cold areas (antarctic).
Accuracy -
Computers will respond to inputs from sensors accurately every time. E.g. a heater will be switched on as soon as the temperature falls below 10°C.
Speed -
Computers will respond to data received from sensors very quickly. E.g. as soon as an infrared sensor detects an intruder the alarm will sound.
Examples of Devices that are controlled by a Computer
Key Words:
Security Light, Alarm System, Automatic Heating System, Automatic Greenhouse.
The following examples discuss a number of devices that can be controlled by a computer:
Security Lights
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 Security lights use infra-red sensors to detect movement.
Security lights with built-in infra-red sensor

Video of Infra-Red Security Light
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Movement is detected when something (man or beast) breaks the infra-red beam. When this happens, the system will turn on the light.

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If nothing else breaks the beam after a period of time, the system will turn the light off.

 
Burglar Alarms
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Burglar alarms work in almost the same way as a security light system.
A modern alarm system with infra-red sensors
Input -
Infra-red sensor detects movement when the sensor is broken and this information is sent to the computer
Process -
Computer makes the decision to sound the alarm
Output -
Alarm is activated.

 
Central Heating
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Modern central heating systems can be programmed to maintain a constant desirable temperature.

Let's imagine our perfect room temperature was set at 25°C - we could use sensors and a computer to:
  • Maintain the optimum temperature of 25°C
  • Turn heating off when it rises above 25°C
  • Turn heating on when it falls below 25°C
Programmable heating system
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Here is how it would work:
 
Input -
Heat sensor detects the current temperature and sends this data to the computer built into the heating system
Process -
Computer would check the sensor heat data against the temperature setting stored in it's memory. Computer decides if the heating needs to be turned on (or off)
Output -
Heating is switched on or off.
 
Computer Controlled Greenhouse
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Automatic greenhouses can provide the optimum conditions for growing plants by using computer control.

Computers can be used to monitor conditions and control a range of applications (devices) to keep the perfect conditions constant.
Computer controlled greenhouses automatically
detect humidity levels and switch sprinklers on when
the soil becomes too dry

Sensors needed to collect data:
  • Light sensor
  • Moisture sensor
  • Heat sensor
Control applications (devices) needed:
  • Grow lights to make plants flourish
  • Motor to turn sprinkler on if plants need water
  • Heater to warm the greenhouse
  • Motor to open window vent to cool greenhouse down if it gets too hot.
 

Click Image to zoom
How the system works:
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Computer reads data from sensors and compares it to preset values.
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If it is too hot = heater turned off and vent opened.
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If it is too cold = heater switched on and vent is closed.
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If there is enough light = grow light switched off.
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If it is too dark = grow light switched on.
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Wet soil = sprinkler switched off.
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Dry soil = sprinkler switched on.
NOTE!
The process will repeat constantly. Sensors continually feed new data into the system and the computer will make decisions based on that data.
 
Other Examples.....
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Other examples of devices that can be controlled by a computer include:
  • Automatic Cookers
  • Automatic Washing Machines
  • Microwaves Ovens.

 

These devices were discussed in section 6.2: The effects of ICT on society