conditions and loops day 4

Conditions and loopsDay 4

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/

Sound in NXT-G

Kelly §6 Make some noise!


The SOUND block

1. This icon shows whether the block will play a sound file or a tone.

2. This icon shows whether the block will start or stop playing a sound.

3. This icon shows the block’s volume. An icon with four orange bars is set to the loudest volume.

4. You can drag data wires from other blocks to this block’s data hub that will affect the Sound block’s properties.


Kelly's example, reversed

Spot, move forward 1 rotations at 50% power coasting to a stop and then play me a C note for 2 seconds at 75% volume.


MoveSound.rbt

Sound in NXC


Two useful sound functions

DefinitionsPlayTone(frequency, duration)PlayFile(filename)

ExamplesPlayTone(440, 500); Wait(500);PlayFile(“Startup.rso”);

Note that PlayTone executes immediately, so that all by itself, it does not play for 500 ms; it relies on Wait to actually extend the duration to the one specified.


Do Kelly's example in NXC

TRIBOT, move forward 1 rotation at 50% power coasting to a stop and then play me a C note for 2 seconds at 75% volume.


MoveSound.nxc

task main()

{

RotateMotor(OUT_AC, 75, 360);

PlayTone(1047,2000);

Wait(2000);

}

Waiting

Kelly §10 Wait for it!


Waiting

The robot is almost always waiting to do something, even when it is already doing something: TRIBOT is moving towards a black line, waiting for the Light

sensor to detect it. TRIBOT is preparing to throw a ball at a target, waiting for the

Touch sensor to be pressed and released. TRIBOT is rolling towards the wall, waiting for the Ultrasonic

sensor to detect it. TRIBOT is sitting at the start line, waiting for the Sound sensor to

hear me yell “Go!”.


Conditions

The WAIT block will stop waiting when specific conditions are met.

The conditions are usually given by some kind of sensor feedback.

The blocks for each condition can be found in two ways:Common palette > Wait.By changing the setting from Time to Sensor on the

Time WAIT block.


The conditions

Time waitTouch sensor waitLight sensor waitUltrasonic sensor waitNXT Buttons waitRotation sensor waitReceive Message wait


A simple test of a condition

TRIBOT, move forward for an unlimited duration at a power of 50 until the Touch sensor is pressed.


MoveTilTouch.rbt


A more complex example

SPOT, move forward for 1 rotation at 50% power, brake, and beep. If your Light sensor detects a light level greater than 30, move backward 1/2 rotation at 50% power, coasting to a stop.


MoveTilLight.rbt

Conditions in NXC


A complication

The sensor functions in NXC do not include this ability to wait; all they do is read sensor values.

So you have to add the condition that the sensor value is supposed to meet, yourself.


If

There are two optionsif (condition) consequence

if (condition) consequence else alternative

Examplesif (x == 1) y = 2;

if (x == 1) { y = 2; z = 3; }

if (x == 1) y = 3; else y = 4;


We can’t do the simple test

TRIBOT, move forward for an unlimited duration at a power of 50 until the Touch sensor is pressed.

PROBLEM: there is no ‘unlimited’ parameter for any of the NXC movement functions, so we skip this task, though the next slide shows what we would want the program to look like.


MoveTilTouch.nxc

task main()

{

OnFwd(OUT_AC, 50);

if (Sensor(S1) == 1)

{

Off(OUT_AC);

}

}


The more complex example

TRIBOT, move forward for 1 rotation at 50% power, brake, and beep. If your Light sensor detects a light level greater than 30, move backward 1/2 rotation at 50% power, coasting to a stop.


MoveTilLight.rbt

task main(){RotateMotor(OUT_BC, 50, 360);PlayTone(1047, 500);Wait(500);if (Sensor(S3) > 30)

{ RotateMotor(OUT_BC, 50, -180);}

}

Loops

Kelly §11 Round and Round


How would you do this?

TRIBOT, display the output of the Light sensor briefly (500ms) 10 times.


The LOOP block

The LOOP block repeats what is inside it until a condition is met.The loop break conditions are the same as the

WAIT conditions.

You drop a block inside a loop by grabbing the block, holding down the mouse button, and dropping it inside when the loop expands.


Go ahead and do it

TRIBOT, display the output of the Light sensor briefly (1s) 10 times.


DisplaySensorLoop.rbt

Loops in NXC


REPEAT

The repeat command, repeat(t) {}, repeats what is in the curly brackets for the number of times given by t.


Convert the example to NXC

TRIBOT, display the raw output of the Light sensor briefly (1s) 10 times.


DisplaySensorLoop.nxcint light;

string text_light;

task main()

{

repeat(10)

{

light = Sensor(S3);

txt_light = NumToStr(light);

TextOut(0, LCD_LINE4, txt_light);

Wait(1000);

}

}

More practiceProgram each bit of pseudocode in NXT-G

and then in NXC.

My suggestion follows each bit of pseudocode, so don’t look ahead until you

are finished with your program!


Follow up

TRIBOT, display the output of the Light sensor briefly (1s) 10 times and beep after each display. Laugh when you are finished.


SensorLoopSound.rbt


SensorLoopSound.nxcint light;string text_light;task main(){

repeat(10){

light = Sensor(S3);txt_light = NumToStr(light);TextOut(0, LCD_LINE4, txt_light);Wait(1000);PlayTone(1047,500);Wait(500);

}PlayFile(“Laughing 02.rso”);Wait(1000);

}


Epilog on scope

Note the difference being in the loop versus being out of the loop makes. PlayTone is played 10 times, because it is in the loop. PlayFile is only played once, because it is not in the loop.

The effect of an expression like repeat is known as its scope, and in NXC the scope of an expression is stated explicitly by means of the curly brackets.


Thought experiment

How would you make TRIBOT move forward and then turn right -- four times?By dropping in 8 MOVE blocks, each with the

same settings (one for each forward move, and one for each turn).

Does this sound like a good usage of your time?No!


The pseudocode

TRIBOT, move forward for 0.5 s at 50% power and then make a 90° turn for 0.65 s also at 50% power. Do this 4 times.


RepeatTurn.rbt


Turning in NXC

You may have noticed that the NXC movement functions do not have the nice ‘steering wheel’ ability that NXT-G has.

The trick to turning in NXC is to reverse a motor. I’ll leave it up to you to figure out which one.


RepeatTurn.nxc

task main()

{

repeat(4)

{

OnFwd(OUT_BC, 50);

Wait(500);

OnRev(OUT_C, 50);

Wait(650);

}

}


Mix them up

TRIBOT, move forward for 1 rotation at 50% power and coast. If your Light sensor detects a level greater than 20, beep and move backward 1/2 rotation at 50% power, coasting to a stop. Do this 3 times, then say the number ‘three’.


MoveLightLoop.rbt


MoveLightLoop.nxctask main(){

repeat(3){

RotateMotor(OUT_BC, 50, 360);if (Sensor(S3) > 20) {

PlayTone(1047,500);Wait(500);RotateMotor(OUT_BC, 50, -180);

}}PlayFile(“03.rso”);Wait(1000);

}


Next time

Quiz 1This will just be a quiz on the blocks.

More loops, switching.Random numbers.'Line Follower' - project done in class

conditions and loops day 4

Documents