Selasa, 23 September 2014
Control Application is split into two parts: turtle graphics and the use of sensors to control or monitor applications.
I. Turtle Graphics
A ‘turtle’ is an on-screen object that follows command given to it by the user. As the turtle moves around the screen it drags a ‘pen’ that leaves a trail behind it.
The command language is called ‘LOGO’.
What is LOGO?
LOGO (also known as 'Turtle Graphics') was developed in 1967 as a way to teach
children basic computer programming.
In LOGO, a curser (called a turtle) can be controlled and moved around the screen by
inputting simple commands. As the curser moves around the screen it draws a line.
Here are some examples of LOGO commands being used to draw simple shapes. You will practice drawing each shape in an online
version of LOGO which can be accessed by clicking the link in the grey box found on the right of each example.
LOGO commands to draw it:
PENDOWN
FORWARD 60
RIGHT 90
FORWARD 60
RIGHT 90
FORWARD 30
RIGHT 90
FORWARD 30
LEFT 90
FORWARD 30
RIGHT 90
FORWARD 30
LOGO commands to draw it:
PENDOWN
FORWARD 40
RIGHT 90
FORWARD 20
PENUP
FORWARD 10
PENDOWN
FORWARD 20
RIGHT 90
FORWARD 40
RIGHT 90
FORWARD 20
PENUP
FORWARD 10
PENDOWN
FORWARD 20
(using REPEAT and ENDREPEAT)
Option 1:
PENDOWN
FORWARD 30
RIGHT 90
FORWARD 30
RIGHT 90
FORWARD 30
RIGHT 90
FORWARD 30
Option 2:
PENDOWN
REPEAT 4
FORWARD 30
RIGHT 90
ENDREPEAT
II. Application Using Sensors
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:
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.
In both cases, sensors are used to send data to a computer where the data is processed – it is what happens next where the differences occur:
In monitoring, the computer simply reviews the data from the sensors
(by comparing it to data stored in memory) and updates its files and/or gives a warning signal if the values are outside given parameters. No changes to the process are made during monitoring.
In control applications, the computer again reviews the data from the sensors (by comparing it to data stored in memory). But if the values are outside the given parameters it takes action to try and get the values within acceptable ranges. It does this by sending signals to devices controlling the process (such as motors, valves, etc.).
Advantages of Using A Computer Control Devices
Cheaper
If a computer is monitoring and controlling applications, you don't 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.
Radioactive sites can be too dangerous for people to work in.
Examples:
1. Burglar Alarms
Burglar alarms work in almost the same way as a security light system.
Input - Infrared 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
a modern alarm system with infra-red sensors
2. Central Heating
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
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.
3. Computer Controlled Greenhouse
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.
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.
III. Robotics
