1. IGCSE ICT
Control Systems

2. Objectives
True control system is when the computer is controlling the output dependent on information from sensors about what is happening.
Be able to describe a number of uses, giving the hardware and software requirements.
Be able to describe the applications that these uses can be put to.
Computers can control systems far more accurately, and respond to changes far more quickly than a human could

3. IPO (INPUT PROCESS OUTPUT) What is the role of the processor in any control system?

4. What is a control system?
Uses microprocessors or computers to control certain physical conditions
Sensors take measurements, then A/D converter converts them into digital signals
The measurements are compared to stored (predefined) values
Processor makes a decision based on the comparison
Control output devices will be used

5. Examples of control systems
Turtle Graphics (LOGO)
Control of Lights and Lamps
Traffic Control System
Control of Washing Machines
Robotics
Burglar Alarms
Central Heating
Video Recorders
Microwave Ovens
Control of Automatic Cookers
Central Air Conditioning
Computer-controlled Greenhouses

6. Usually measured by Sensors
Physical conditions (variables) that are controlled by computer/microprocessors include:
Temperature
Pressure
Humidity
Light
Moisture etc

7. Hardware requirements: Input
Numeric Keypad
Push buttons/switches
Temperature sensor
Moisture sensor
Pressure sensor
Light sensor

8. Processor ADC (A/D Converter) DAC (D/A Converter) Timer
Algorithms to compare data from sensors to predefined values or ranges
Signals sent to control output devices

9. Hardware requirements: Output
Robot
Fans
Heaters
Boilers
Buzzer/alarm
Lights
LED display
Motors

10. Computer-Controlled Greenhouse
ADC
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

11. IPO Computer-Controlled Greenhouse
Inputs
Processes
Outputs
Light Sensor
Sensors monitor amount of light , moisture, temperature continuously
Light
Moisture Sensor
Analogue data from sensors converted to digital using ADC
Water Pump
Temperature sensor
Temperature compared to preset range/value
Heater
Signal sent to turn on heater and use motor to close window if too cold
Motor
Signal sent to turn off heater and use motor to open windows if too warm
Signal to actuator to turn water pump on if soil dry or off is soil is moist

12. Air conditioning
Sensors are needed to monitor temperature (continuously)
Microprocessor compares the temperature with a preset value/range
Depending on result microprocessor causes the fan motor to speed up or slow down
Fan motor switched on or off

13. IPO Central Air Conditioning
Inputs
Processes
Outputs
Buttons/touchscreen
Sensors monitor temperature continuously
LED display
Contact switch
Analogue data from sensors converted to digital using ADC
Fan
Temperature sensor
Temperature compared to preset range/value
Buzzer
Pressure sensor
Signal sent to actuator to switch fan on or off

14. Closed Loop system Output directly affects the input
No human intervention is necessary
Good for situations where control is required 24/7, or in a dangerous/difficult environment

15. Refrigeration Sensors continuously monitor temperature
Microprocessor compares the temperature with a preset value/range
Depending on result microprocessor causes the fan motor to speed up or slow down
Fan motor switched on or off

16. IPO Refrigeration Inputs Processes Outputs Contact switch (door)
Sensors monitor temperature continuously
LED display
Pressure sensor (door)
Analogue data from temperature sensor converted to digital by ADC
Compressor
Number pad or dial
Temperature compared to preset range/value input by user
Buzzer
Temperature sensor
Signal sent to actuator to switch compressor on if temp is too high
Signal sent to actuator to switch compressor off if temp is OK

17. Central heating
Sensors are needed to monitor temperature (continuously)
Microprocessor compares the temperature with a preset value/range
Microprocessor controls two actuators
one opens gas valves in the boiler
the other switches the pump on

18. IPO Central Heating Inputs Processes Outputs Touch screen
Sensors monitor temperature continuously
LED display
Number pad or dial
Analogue data from temperature sensor converted to digital by ADC
Radiators
Temperature sensor
Temperature compared to preset range/value input by user
Signal sent to actuators to switch pump on & open valves if temp is too low
Signal sent to actuator to switch pump off/close valves if temp is OK

19. Automatic Cooker (Microwave Ovens are very similar, more features, most can be set to turn themselves on and off at particular times)
2 User inputs:
Desired temperature
Length of cooking time
Sensor measures the temperature in the cooker
Microprocessor controls a heating element to keep the temperature constant
Microprocessor controls a buzzer to inform the user when the time is up.

20. IPO Automatic Cooker Inputs Processes Outputs Touch screen/Keypad
Sensors activated
Temperature Sensor
Checks if temperature greater than the temperature from the sensor
Buzzer
Timer
Heater
Analogue data from sensors converted to digital by ADC

21. Burglar Alarm
User inputs a code to set the alarm when they leave the house and a code to stop the alarm being triggered when they re-enter the house
Detects when a door or window is open using a simple magnet and contact switch
If the movement sensor senses something, the computer can immediately decide what to do

22. IPO Burglar Alarm Inputs Processes Outputs Touch screen/Keypad
Sensors activated
Light Sensor
Checks if lights have been turned on
Buzzer/Alarm activated
Movement Sensor (senses infra-red light changes)
Detects if something is moving within a certain range
Magnet/Contact Switch
Checks if doors/windows are open
Analogue data from sensors converted to digital by ADC

23. Software requirements
Control software