 5.2.4
Software: Control
Languages
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Points: |
- Candidates should be able to create instructions to respond to data from sensors;
- Candidates should be able to write a sequence of instructions to control a screen image or external
device such as lights, buzzers, sound or turtle, using repeated
instructions, procedures and variables as appropriate;
- Candidates should be able to identify typical applications involving the use of
control and data
logging software.
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You are not expected to have a detailed understanding of
programming languages at
GCSE level. However, the exam paper is likely to have a question on using or interpreting
Logo commands.
Control:
 Control
technology is used to allow a computer to respond to data that has been
captured or recorded using sensors.
An example would be a control system to maintain the correct conditions in a
greenhouse automatically.
- Sensors could measure the temperature and amount of light.
- A control program would make decisions if the readings got outside a
certain range.
- Motors could open windows if the temperature got too high or switch on
heaters if it got too low.
- Motors could close blinds if the light was too much or relays could switch
on lights if it was too dark.
The control program is a series on instructions written in a particular programming language. This language has commands to
read input sensors, process the data in some way and make
decisions and then control outputs such as
motors, lights, relays etc.
Many control languages have the following additional features:
- They can use and alter variables. This is a way of giving a number
a label (such as A=12). The value of the variable can be easily altered
(i.e. A = A + 1 would add 1 to whatever A was before) or used in a
program in decisions (i.e. IF A >= 10 MOTOR OFF).
- The can use LOOPS to make part of a program repeat until a certain
condition is met
(i.e. REPEAT
T = TEMPERATURE READING (from a
sensor)
UNTIL T = 90)
- The can use procedures (or macros) . These a
self-contained bits of program that are used for commonly repeated tasks in
the main program. This avoids having the same bits of instruction coded
repeated in lots of different places in one program. A procedure is
usually given a simple name by the programmer and then the main program uses
this name to run it.
Types of Control Languages:
- Command Line languages:
- These use a wide range of different commands and they are usually typed
into the computer line by line.
- When the program runs it starts at the first line and then either moves
through the program one line at a time or is directed from one set of
instructions to another depending on the way the program is written.
- The way the commands are entered has to be exactly right (this is
called the SYNTAX) and it can take a long time to learn.
- Unfortunately, many different control languages will use a different syntax to do
exactly the same job. For example:
| Program 1 |
Program 2 |
REPEAT 10
T=TEMPERATURE
IF T>10 THEN END
END REPEAT |
LOOP
T=TEMPERATURE
UNTIL T>10
END |
- Logo:
- This is simple command line computer language that is usually
used to draw shapes on a computer screen but it can also be used to move a motorised buggy or
"turtle" around the floor.
-
 Example Logo instructions:
- REPEAT 4 [FORWARD 20 RIGHT 90 ]
- These instructions would make the 'turtle' draw a square. It would
repeat 4 times the commands to move forward 20 and then turn right 90 degrees.
- Flowsheets:
- An example of this is
Logicator. To construct a program, commands are dragged and dropped
onto a screen and connected by lines.
- When the program starts it moves from one command to the next along the
connecting lines.
- The individual commands can be edited and include Input commands, output
commands and decision commands etc.
- Flowsheet programs are usually easier to follow than command line
programs.
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