Sensors and Control
Sensors
Sensors are often used as part of a feedback cycle. They collect data continuously and are typically linked to a control program that specifies acceptable levels, eg the minimum and maximum temperature in a greenhouse. The control program decides what to do next based on the data it's fed by the sensors.
Logo
Logo is a simple computer programming language which can be used to control devices. For example, a small robot known as a A robot that can be programmed using the programming language Logo to carry out simple commands, eg forwards and backwards. can be moved around the floor using logo. Logo is often used with a screen turtle, which is an object on the screen used to simulate how a turtle moves around the floor. There are many An instruction given to a computer. which can be used to control the turtle.
Logo commands
Here are some examples of the most common Logo commands:
| Command | Action |
| FORWARD 50 | move forward 50 steps |
| BACK 50 | move backward 50 steps |
| LEFT 90 | turn 90° left |
| RIGHT 90 | turn 90° right |
| PENDOWN | lower pen and begin drawing |
| PENUP | raise pen and cease drawing |
| Command | FORWARD 50 |
|---|---|
| Action | move forward 50 steps |
| Command | BACK 50 |
|---|---|
| Action | move backward 50 steps |
| Command | LEFT 90 |
|---|---|
| Action | turn 90° left |
| Command | RIGHT 90 |
|---|---|
| Action | turn 90° right |
| Command | PENDOWN |
|---|---|
| Action | lower pen and begin drawing |
| Command | PENUP |
|---|---|
| Action | raise pen and cease drawing |
These commands can be used to draw a square on the screen:
- FORWARD 100
- LEFT 90
- FORWARD 100
- LEFT 90
- FORWARD 100
- LEFT 90
- FORWARD 100
- LEFT 90
Repeating commands
The same commands can be written more quickly using the REPEAT command, for example:
REPEAT 4 [FORWARD 100 LEFT 90]
This single command would have the same effect as the eight individual commands above - it draws a square.
The REPEAT command can be used to create any number of patterns. For example, a shape similar to a spirograph was created with this command:
REPEAT 30 [FORWARD 100 RIGHT 156]
Storing a series of commands like this creates a simple program. The order of the commands in a program is vital. If it is in the wrong order, the program will not work as expected.
Computer programming languages are very fussy. Any errors, however small, will cause the program not to work. The computer won't like spelling mistakes or, for example, if you forget to put a space between FORWARD and 50.