IGCSE ICT Control Systems

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

Software requirements Control software