variables, logic and sensors day 3 computer programming through robotics cpst 410 summer 2009

Variables, logic and sensorsDay 3

Computer Programming through Robotics

CPST 410

Summer 2009

7/1/09 Harry Howard, CPST 410, Tulane University 2

Course organization

Course home page (http://robolab.tulane.edu/CPST410/)

Lab (Newcomb 442) will be open for practice with 3-4 Macs, but you can bring your own laptop and all robots.

http://robolab.tulane.edu/CPST410/


Phot

os


Mindstorms NXT 2.0

You can preorder it now, and it will ship by 1 Aug 2009.

$ 279.99http://shop.lego.

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Wired!

Kelly §7


Hubs and wires

Kelly's introduction to wiring is not based on real NXT-G blocks, but rather on ones he made up for the sake of perspicuity.

I would rather you work with real blocks, so I will ignore his presentation. You should still read it, however.

We will go back to what we skipped in §3 (because it was wrong).


Data hubs

The settings of many blocks can be changed from other parts of the program through their data hub.

Create a new program "VariableMove".Drop a MOVE block into it.

Change its duration to degrees.Make sure your motors are set correctly.

Put your cursor at the bottom of the MOVE block and try to pull down the indented line.


The MOVE block data hub

Running the cursor over each icon reveals which setting it accepts.

If you have an Internet connection, click on the 'More help' link at the bottom right.


The VARIABLE block

To illustrate the usefulness of the data hub, we will try out a new block that does not come up in detail until §18, the VARIABLE block.

Change to the Complete palette (the three interlocking squares at the bottom left).

Select the big orange plus sign (Data),pull out a suitcase (Variable), anddrop it in front of the MOVE block.


Using the VARIABLE block

The list shows the three types that a variable can have: Logic, Number, and Text.Number and Text mean what they say; Logic we will

take up later.Change the type from Logic to Number.

Note that the action is set to Read and the value (0) is grayed out so that you cannot change it.We want to change it, so set it to Write and change the

value to 180.In programming terms, we have declared a variable of

type number and name 'Number 1' and set its value to 180.


Using the VARIABLE block, cont.

However, we cannot use the variable yet. We have to make it available to the rest of the program by

reading it, but a VARIABLE block can only be set to read or write, not both.

So drop another VARIABLE block after the first. Set its type to Number. Set its action to Read.

Now pull out a wire from its output plug and connect it to the MOVE input plug for Duration. You might not get it right the first time, but persevere.


The program

Now we can use the variable.

Save, download, and run the program.

How far does your Tribot go? 180 degrees, because the

setting on the MOVE data hub for Duration only accepts degrees.


Let's display something

Drop a DISPLAY block after the MOVE block.What should we display?

How about the number of degrees the wheels turn?Pull down the data hub of the DISPLAY block.

Where would we connect the VARIABLE block to display its value?

CRUCIAL LIMITATION: Type cannot change. Most of the input plugs are for numbers, but these

numbers are used in positioning something on the LCD screen (and selecting the diameter of a circle).


Type conversion

The trick is to display the number 180 as the text "180".

But these two objects are of different types.NXT-G only supplies one block for type

conversion, in the Complete palette under the Advanced icon (four squares).The NUMBER TO TEXT block.


The NUMBER TO TEXT block

Drop one between the MOVE and DISPLAY blocks.

Pull a wire out of the Duration output plug of the MOVE block and connect it to the input plug of the NUMBER TO TEXT block.Again, this may take some trial and error.

Pull a wire out of the output plug of the NUMBER TO TEXT block and connect it to the Text input plug of the DISPLAY block.


The program

Remember that the DISPLAY block is very fast, so pull a TIME WAIT block out of the Common palette and drop it after the DISPLAY block. Set it to 10 s.

Save, download, and run the program. What happens?


Wires and plugs

[A] Input plug

[B] Output plug

[C] Number data wire (yellow)

[D] Logic data wire (green)

[E] Text data wire (orange)

[F] Broken data wire (gray)


Play time

Take a few minutes to play with the program.


First look at BricxCC

Open BricxCC and move the Brick Command Center window to the left so that the Templates window is visible (see next slide).


Now go to the File menuand start a new program.


Reserved wordsidentifiers and keywords, p. 135

__RETURN__ Char Long sub

__RETVAL__ const Mutex switch

__STRRETVAL__ continue priority task

__TMPBYTE__ default repeat true

__TMPWORD__ do return typedef

__TMPLONG__ else safecall unsigned

Abs false Short until

Asm for Sign void

Bool goto Start while

break if Stop

Byte inline string

Case int struct


Parsing errors

Usually because of missing or incorrect punctuation: } ; ) The parser expects these things in certain places. If its expectations are not met, it gives an error message. It also gets thrown off track for the upcoming code and

thus generates lots of error messages only because of the first one.

Variables in NXC

Hansen p. 135ff


Variables

NXC has about 11 types of variables.Today we will concentrate on the single

numbers.Since a number can take up a lot of storage

space depending on how precisely it is specified, we want to be frugal with them.


Simple numerical variables

Keyword for type Description

short, int 16 bit; first bit indicates sign

unsigned int 16 bit; no bit for sign; rare

long 32 bit; first bit indicates sign

unsigned long 32 bit; no bit for sign; rare


Variable declaration

Variables are declared using the keyword for the type, followed by a list of variable names which are separated by commas and terminated with a semicolon:int x;

long y, z;

An equals sign can be followed by an initial value:int x=1, y=2, z;


Constants

When a program contains a value that does not change during execution, it's a good idea to give it a name to make the program easier to understand.

This is done in NXC with a macro definition using the compiler directive #define, e.g.;#define METER2MM 1000

#define DEG2ROT 360 Compiler directives do not end in a semicolon. During compilation, each macro is replaced by its value.

True or false?Feedback

Kelly §8-9


Robot does something

(motor cortex)

Environment changes

(sensory cortex)

feedforwardfeedback

The place of feedback


Robot does something

(motor cortex)

Environment changes

(sensory cortex)

feedforward

feedback

The complete system

Robot decides

(prefrontal cortex)

?


All the sensors are in the Complete palette


Sensor overview

NXT Sensor Conditions

Touch Pressed, released, bumped

Sound > n (0 - 100)

Light > n (0 - 100)

Ultrasonic < n (0 - 100)

Rotation n (0 - 360)


Sensors and conditions

Once a sensor senses that its condition has been met, it produces a value of Yes (or True or 1).

Otherwise, it produces a value of No (or False or 0).

Such values of yes or no are known as logical values (though binary is just as accurate, and maybe more).


Check the sensors

Plug a sensor into a sensor port (the ones along the bottom).

Create a program that displays the output of the sensor on the screenHint: See if any of the output plugs on the data

hub help.


DisplaySensor.rbt

Calibration

Kelly §23


Different enviornments

The Light and Sound sensors can respond differently in different environmentsFor example, the maximum in a brightly lit

room will be different from the maximum in a dimly lit room

NXT-G provides a CALIBRATION block to account for this kind of variation


The CALIBRATION block

Found in Complete > Advanced

Sets the minimum (0%) and maximum (100%) values detected by a sound or light sensor.


Usage

Although a single one can set both the min and max, it is safer to check each extreme separately, i.e. use one CALIBRATION block for the min and another for the max.

How do you decide the min and max?Design a program to calibrate the light

sensor for our room.

Sensors in NXC


Sensor options

You may recall that the sensor blocks had lots of options.

These have to be set by special statements in NXC.

There are three things to setthe sensor port: 1, 2, 3, 4the sensor type: light, sound, touch, etc.the sensor mode: how the data is collected


Sensor port names

There are three naming schemesS1, S2, S3, S4IN_1, IN_2, IN_3, IN_4SENSOR_1, SENSOR_2, SENSOR_3,

SENSOR_4


Set sensor type to a port

SetSensorLight(port)SetSensorSound(port)SetSensorTouch(port)


Sensor type constants

Sensor Type Meaning

SENSOR_TYPE_NONE no sensor configured

SENSOR_TYPE_TOUCH NXT or RCX touch sensor

SENSOR_TYPE_LIGHT_ACTIVE NXT light sensor with light

SENSOR_TYPE_LIGHT_INACTIVE NXT light sensor without light

SENSOR_TYPE_SOUND_DB NXT sound sensor with dB scaling

SENSOR_TYPE_SOUND_DBA NXT sound sensor with dBA scaling


Sensor mode constants

Sensor Mode Meaning

SENSOR_MODE_RAW raw value from 0 to 1023

SENSOR_MODE_BOOL boolean value (0 or 1)

SENSOR_MODE_EDGE counts number of boolean

transitions

SENSOR_MODE_PULSE counts number of boolean periods

SENSOR_MODE_PERCENT value from 0 to 100

SENSOR_MODE_ROTATION rotation (16 ticks per revolution)


SetSensor function

It is convenient to set the type and the mode at the same time.

The SetSensor function makes this a little easier by providing a set of standard type/mode combinations (on the next slide) and a single function to call them:SetSensor(port, constant configuration)

ExampleSetSensor(S1, SENSOR_TOUCH);


Sensor type-mode constants

Sensor configuration constant

Type Mode

SENSOR_TOUCH SENSOR_TYPE_TOUCH SENSOR_MODE_BOOL

SENSOR_PULSE SENSOR_TYPE_TOUCH SENSOR_MODE_PULSE

SENSOR_EDGE SENSOR_TYPE_TOUCH SENSOR_MODE_EDGE

SENSOR_LIGHT SENSOR_TYPE_LIGHT SENSOR_MODE_PERCENT

SENSOR_ROTATION SENSOR_TYPE_ROTATION SENSOR_MODE_ROTATION


Reading sensor values

Once these options have been set, the processed sensor reading can be read from its port using the function: Sensor(port)

Example x = Sensor(S1); // read sensor at port 1

The ultrasonic sensor has its own function: SensorUS(port)x = SensorUS(S1); // read ultrasonic sensor at port 1


Next time

P1This will just be a quiz on the blocks

Whatever we did not finish todayRandom numbers'Line Follower' - project done in class

variables, logic and sensors day 3 computer programming through robotics cpst 410 summer 2009

Documents

variable block

harry howard

new block

block data hub

variable of type number

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