Lego nxt light sensor calibration

BASIC COURSE

2 Contence | Cursus Basiskennis LEGO MINDSTORMS

C ON T E N C E

CONTENTS ....................................................................................................................................... 2

PREFACE .......................................................................................................................................... 3

USE OF SENSORS ............................................................................................................................. 4

INTRODUCTION ................................................................................................................................... 4

TASK 1 : USING MOTORS ....................................................................................................................... 4

WHEN DO YOU USE A MOTOR? ...................................................................................................................... 4

HOW TO USE A LEGO MOTOR ......................................................................................................................... 5

HOW TO USE THE “DISPLAY”SCREEN ................................................................................................................ 5

TASK .......................................................................................................................................................... 5

TASK 2 : USING THE TOUCH SENSOR ......................................................................................................... 7

WHAT IS A TOUCH SENSOR AND WHAT CAN YOU USE IT FOR? .............................................................................. 7

HOW TO USE THE LEGO TOUCH SENSOR ........................................................................................................... 7

TASK .......................................................................................................................................................... 8

TASK 3 : USING A LICHTSENSOR ............................................................................................................. 9

WHAT DO YOU USE THE LIGHT SENSOR FOR? .................................................................................................... 9

HOW DO YOU USE THE LEGO LIGHTSENSOR? ................................................................................................... 10

HOW TO CALIBRATE THE LIGHT SENSOR .......................................................................................................... 11

TASK ........................................................................................................................................................ 11

TASK 4 : USING THE ULTRASONIC SENSOR ................................................................................................ 13

WHAT IS AN ULTRASONIC SENSOR AND WHAT IS IT USED FOR? ........................................................................... 13

HOW TO USE THE LEGO ULTRASONIC SENSOR .................................................................................................. 13

TASK ........................................................................................................................................................ 14

TASK 5 : USING THE SOUND SENSOR ....................................................................................................... 15

WHAT IS A SOUND SENSOR AND WHAT DO WE USE IT FOR? ............................................................................... 15

HOW TO USE THE LEGO SOUND SENSOR ........................................................................................................ 15

TASK ........................................................................................................................................................ 16

Cursus Basiskennis LEGO MINDSTORMS | Preface 3

P R E F AC E

This course material is the result of a Comenius project 2007 – 2009 between VTI Veurne (Belgium), Budai

Középiskola (Hungary), ISS Deambrosis Natta (Italy), Portalens Gymnasium Uddevalla (Sweden) and Vocational

High School of Orestiada (Greece).

In 2007 these schools decided to start a LEGO MINDSTORMS project.

The purpose was to get the students of these schools communicating about the project, having them carry out

experiments with the LEGO NXT and ultimately develop attractive course material for students / teachers.

Very soon other teachers became interested and the LEGO NXT motivated them to introduce it in their lessons.

Therefore a basic course was made up to enable starters to get introduced to the NXT.

At our school group work exercises will be introducing LEGO NXT in the ICT lessons of the first grade of

secondary education, without dealing with sensors though.

In the second grade the students will learn how to work sensors and they will try more difficult exercises with

LEGO NXT..

In the third grade they will start using LabVIEW to program the LEGO NXT.

Please, enjoy!

4 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

U S E OF S E N S ORS

I N T R O D UC TI O N

We subdivide the class into groups of 3 to 4 students. Each group has to complete 5 tasks. Whenever a group

thinks they are ready to do the task they ask the teacher to take their time. The groups can have 3 tries to

correctly complete each task. The teacher notes down the time in the table. If a group does not manage to

complete a task they get the maximum penalty time of 25 seconds for that task.

Group 1 Group 2 Group 3 Group 4 Group 5

Task 1

Task 2

Task 3

Task 4

Task 5

All tasks can be done on a standard classroom table.

T A S K 1 : U SI N G M O T O R S

W H E N D O YO U U S E A M O T O R ?

In our daily life a lot of things need a motor. Everyone knows that.

Can you give some examples?

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H O W T O U SE A L E G O MO T O R

You can drive a little car with a LEGO motor.

But you could also use a motor to have it hit a ball.

H O W T O U SE T H E “ D IS P L A Y” SC R E EN

Switch on the NXT by pressing the orange button .

The main menu appears. Press the right hand button twice and you will get the “Display” or ‘View’ screen.

Press the orange button again.

With the display you can determine the exact distance that the NXT has to drive. In order to find the number of

revolutions for a certain distance you scroll with the arrow buttons until you find the button ‘Motor rotations

R’. Press the orange button once more. Next you have to select which gate the motor is connected to. If you

now push the robot forward you will see how many rotations it makes.

T A S K

What you need:

• NXT basic model • an extra motor mounted onto the NXT and built in compliance with the

model in the manual

• ball with a little holder built like the model in the manual • black tape for the circuit.

Here you can select a

gate on the NXT.

Here you can define the direction:

forward, backward or stop.

Here you make the NXT turn

under a well defined angle..

Here you can define the next action

the NXT has to take.

Here you can define the distance

the NXT has to cover.

Here you can define the

power of an engine.

6 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

Task

The NXT basic model has to complete the course as represented below. At the end of the course, there is a

little ball. You have to knock away this small ball with the extra motor.

Take care, the NXT robot should stay within the black lines. This can only be done by accurately defining the

angles and by choosing exactly the same starting position with every try. Therefore it can be interesting to

mark this position with a piece of black tape.

See to it that the NXT robot performs the test as fast as possible.

Track

Write down every step of your program in the table below.

Which block do you use? Which are the settings you apply?

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T A S K 2 : U SI N G T H E T OU C H S E NS OR

W H A T I S A T O U C H S E NS O R A ND WH A T C A N YO U U S E I T FO R ?

A touch sensor is a sensor that works as a switch and reacts when you press the button. The sensor signals the

NXT module if it is pressed or not. A good touch sensor can even measure how strong the pressure on the

sensor is. This is measured in Pa.

A touch sensor is used a lot in daily life, but it isn’t that obvious. Can you come up with 2 examples in which

touch sensors are used?

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*………………………………………………………………………………………………………………………………………………

H O W T O U SE T H E L E G O T O U C H S EN S O R

The LEGO touch sensor is a very simple sensor which can only check if the sensor has been pressed or not.

The touch sensor has a hole in the middle in which you can fit an axle. You can build a construction on it that

allows the sensor to “feel” objects better.

You can use the touch sensor in different ways:

A first way in which you can use it, is with the ‘Wait’ block. When using this

block the NXT waits until the touch sensor registers pressure. The robot

can then start on the next task.

A second way to use the touch sensor is by using the ‘Switch’ block. With

this block you can give the robot a task when the touch sensor is pressed

and another task when it is not. This is called true/false programming.

An example: you can have the robot drive forward as long as the touch

sensor isn’t pressed. When the sensor touches an object the robot must

stop.

8 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

T A S K

What you need:

- NXT basic model without sensors

- the touch sensor which you mount at the front of the NXT

- black tape to mark the track

- 2 little vertical boards which will serve as walls.

Task

The goal is to programme your NXT robot so that it keeps to the track and uses the touch sensor.

Have the basic model of the NXT drive forward until it detects the wall with the touch sensor. Next it has to

turn and drive to the other wall and then turn again. Now the robot has to drive to the finish and stop. In the

drawing below you can see the track. You have your robot do the track as fast as possible. It’s not allowed for

the NXT to cross the black lines. You can solve this problem by accurately measuring the angle at the turning

points and by always taking the same starting position. That’s the reason why it can be useful to mark the

starting position with black tape.

Track

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Write down every step of your program in the table below.

Which block do you use? Which are the settings you apply?

T A S K 3 : U SI N G A LI G HT S E N S O R

W H A T D O YO U U S E T HE L I G H T S EN S O R F O R ?

With a light sensor, you can detect different light intensities.

Can you give an example from everyday life in which a light sensor is used?

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10 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

H O W D O YO U U S E T HE L E G O L I GH T S E N S O R?

The new light sensor is an improved version of the somewhat older

MINDSTORMS for schools. This sensor is much more sensitive, so you can do

more precise light measurements on a scale of 0 to 100. It’s also possible to

turn off the infrared light that can be found just below the sensor. In this way

the sensor only measures light of the environment.

Here you can select the port the sensor is connected to.

Here you can set the moment of activation.

Here you can see the If you switch on the button ‘ Generate

current light value. light’ ,the light sensor will generate its own

light that will be reflected onto the light

sensor.

The button ’Generate light’ can be useful.

The button ’Generate light’ can be useful if the light conditions are difficult, such as in very sunny

weather. The sensor only detect differences in how much light reflects off an object. Closer objects

are brighter than further ones, light-color objects are brighter than dark ones, and redder objects will

seem brighter than blue ones.

How do you detect different light intensities on the NXT?

Switch on the NXT by pressing the orange button.

When the main menu appears, you press the right hand arrow twice so that you get ‘View’ on the

screen. Press the orange button again. Now scroll with the grey keys until you find the light sensor.

On the ‘Display’ screen you can now see the brightness that the sensor perceives. You can have the

light sensor generate light with the button ‘Reflected light’ or let it work with the light of the

environment with the button ‘Ambient light’. Select the port which the light sensor is connected to.

Direct the sensor to different objects and you will see the intensity, shown in percentage. Just like

the other sensors you can combine this sensor with the ‘Switch’ block or the ‘Wait’ block.

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You can use the light sensor in different ways.

The first way is with the ‘Wait’ block. The program will wait until the

sensor perceives a certain light intensity. As soon as this condition has

been fulfilled the program will continue running.

The second way is using the ‘Loop’ block. The program part inside the

‘Loop' block will continue until the light sensor measures a specific light

intensity.

The third way is with the ‘Switch’ block. Here you can give the robot a

certain task when the desired light intensity is reached and another task

when this is not the case. This is called true/false programming. So for

example you have the robot drive forward until it meets an object with a

higher light intensity than the selected value and then you have the robot

turn.

H O W T O C AL IB R A T E THE L I G H T S EN S O R

Sensors can sometimes be influenced by their environment. Therefore it is useful to calibrate them to let them

work correctly in every environment. In order to do this the sensor must be connected to a computer (via the

NXT).

Place the sensor block in the programming window and select it.

In the menu you will find the submenu 'Extra'. In this menu you select 'Calibration of sensors'. Ensure the

sensor is connected to the correct gate. Aim the sensor at the darkest place and press the orange button. Next,

aim at the brightest place and press the orange button again. The calibration is now complete. For the NXT the

darkest place now equals 0 and the brightest place 100.

T A S K

What you need:

- NXT basic model with light sensor fitted onto a long arm.

- black tape.

Task

The NXT (basic model equipped with a light sensor) is placed inside an area, defined by a black line (as you can

see underneath). The NXT starts inside the area, at its edge. It has to make a complete lap along the edge of the

area, as fast as possible.

The NXT will have to detect the line with the light sensor and then execute a movement in order to stay in the

area and close to the line. The NXT must be able to fulfill this task no matter where it is positioned to start.

The task has to be completed as fast and accurately as possible.

12 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

Track

Write down every step of your program in the table below.

Which block do you use? Which are the settings you apply?

Cursus Basiskennis LEGO MINDSTORMS | Use of sensors 13

T A S K 4 : U SI N G T H E U LT R A S O N IC SE N S O R

W H A T I S AN U L T R A S ON I C S E N S OR A N D W H AT I S I T US ED F O R?

An ultrasonic sensor is a sensor that can measure distances. The sensor sends and receives a signal. The time

between sending and receiving determines the actual distance to an object. So, the longer it takes for the

sensor to get the signal back, the further away the object is.

This sensor is used in the parking aid system of new cars. In this case the sensor determines the distance

between the cars to prevent the cars from bumping into each other.

Name 2 other examples in which the ultrasonic sensor is used.

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- ………………………………………………………………………………………………………….

H O W T O U SE T H E L E G O U L T R A S O NI C S EN S O R

The ultrasonic sensor created by LEGO has a reliable range from 5 till 220 cm. The distance shown is the

distance measured from the back of the sensor, as it were the rear side of the ‘eyes’ of the sensor.

You can use the sensor with the ‘Switch’ block. With this block you can choose between two conditions: closer

or further away than the selected distance. Similar to a camera a flower suggests nearby, the closer or ‘less

than’ option. The mountain suggests further away, the ‘farther than’ option.

You can also use the ‘Wait’ block. The action of the next block can only start when the condition of this block

has been fulfilled. So the robot waits for the condition to be realized. This condition could be “a distance

smaller than or bigger than a selected value”.

14 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

T A S K

What you need:

- tape, to mark a zone

- LEGO NXT with the LEGO ultrasonic sensor

- free standing table.

Task

You let the robot drive along the edge of the table, but ensure that the robot does not fall off the table. The

robot must always drive within an area of 20 cm from the edge of the table. At the corners of the table the area

is slightly rounded.

Track

Write down every step of your program in the grid below.

Which block do you use? Which are the settings you apply?

Cursus Basiskennis LEGO MINDSTORMS | Use of sensors 15

T A S K 5 : U SI N G T H E S OU N D S E N SOR

W H A T I S A S O U N D S ENS O R A ND WH A T D O W E U S E I T F O R?

The main function of a sound sensor is registering sound. With most sensors you can also register the sound

level. The best known example of a sensor that can measure the sound level is the decibel meter, but a baby

alarm can also register the sound level. If a baby cries too loud the “alarm” in the baby intercom of the parents

will sound: they will hear their baby cry.

Can you think of some examples yourself ?

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H O W T O U SE T H E L E G O S O U N D S EN S O R

We measure the sound level in decibel (dB). When you talk to a

person in a normal voice the sound level will be around 40 to 60 dB.

When you make a lot of noise the membrane of the microphone will

move much more and you will measure a level of sound that is higher

than 90 dB.

The sound level of this sensor is represented in %.

< 5 % : quiet room

5-10% : talking at a distance from the sensor

10-30% : talking into the sensor/ playing background music

30-100% : shouting into the sensor/ very loud music

The sensor can also be turned into dBA mode by a contact point in the data hub.

The human ear is not as sensitive for all frequencies . The dBA mode will adapt the level of the measured sound

more to how we experience the sound level as a human being.

The sound sensor can register the difference between a normal voice and a loud voice. You can programme the

robot to complete a certain task when one person is giving the command and another task when there are

more people giving the command simultaneously.

The sound sensor is also able to recognise several sound patterns. Clapping your hands twice can have a totally

different meaning to the robot than clapping once.

Apart from different sound patterns the sensor also has the capability to register the difference in tone. This

way you are able to programme different commands depending on the pitch.

You can use the sound sensor in different ways:

This block can measure the actual sound level and then send this in a logical signal

(true/false) via the data link. If the sound level is above a certain limit, then the

‘true’ signal will be sent. If it’s under a certain limit it will send a ‘false’ signal.

16 Use of sensors | Cursus Basiskennis LEGO MINDSTORMS

A second way is using the ‘Wait’ block. It allows you to make the NXT robot wait until

the sound sensor registers the required sound level. Once this demand has been

fulfilled, the robot will continue to the next task.

A third way is using the ‘Switch’ block. This way you’re able to give the NXT robot a

task when it does not hear the required sound signal and one when it does. We call

this a true/false function. For example you’re now able to make the robot move

forward as long as the sound sensor doesn’t register 50% of its sound range. When it

does reach this sound level it will perform another task, such as driving around in

circles until the sound drops below 50% again.

T A S K

What you need:

- NXT basic model without sensors

- the sound sensor which is mounted on the side of the NXT

- black tape to mark the starting position

- bell or toy that makes a noise when you drive a lego car into it

- a cardboard box which is used as a garage.

Task

In this task the NXT robot must start from the starting position (S) and activate the bell (B). When the sound

sensor registers the signal the robot has to drive to the garage (G).

Track

Cursus Basiskennis LEGO MINDSTORMS | Use of sensors 17

Write down every step of your program in the grid below.

Which block do you use? Which are the settings you apply?