Conditions and loops Day 4 Computer Programming through Robotics CPST 410 Summer 2009

7/1/09Harry Howard, CPST 410, Tulane University2 Course organization  Course home page Course home page  (  Lab (Newcomb 442) will be open for practice with 3-4 Macs, but you can bring your own laptop and all robots.

Sound in NXT-G Kelly §6 Make some noise!

7/1/09Harry Howard, CPST 410, Tulane University4 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.

7/1/09Harry Howard, CPST 410, Tulane University5 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.

7/1/09Harry Howard, CPST 410, Tulane University6 MoveSound.rbt

Sound in NXC

7/1/09Harry Howard, CPST 410, Tulane University8 Two useful sound functions  Definitions  PlayTone(frequency, duration)  PlayFile(filename)  Examples  PlayTone(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.

7/1/09Harry Howard, CPST 410, Tulane University9 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.

7/1/09Harry Howard, CPST 410, Tulane University10 MoveSound.nxc task main() { RotateMotor(OUT_AC, 75, 360); PlayTone(1047,2000); Wait(2000); }

Waiting Kelly §10 Wait for it!

7/1/09Harry Howard, CPST 410, Tulane University12 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!”.

7/1/09Harry Howard, CPST 410, Tulane University13 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.

7/1/09Harry Howard, CPST 410, Tulane University14 The conditions  Time wait  Touch sensor wait  Light sensor wait  Ultrasonic sensor wait  NXT Buttons wait  Rotation sensor wait  Receive Message wait

7/1/09Harry Howard, CPST 410, Tulane University15 A simple test of a condition  TRIBOT, move forward for an unlimited duration at a power of 50 until the Touch sensor is pressed.

7/1/09Harry Howard, CPST 410, Tulane University16 MoveTilTouch.rbt

7/1/09Harry Howard, CPST 410, Tulane University17 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.

7/1/09Harry Howard, CPST 410, Tulane University18 MoveTilLight.rbt

Conditions in NXC

7/1/09Harry Howard, CPST 410, Tulane University20 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.

7/1/09Harry Howard, CPST 410, Tulane University21 If  There are two options if (condition) consequence if (condition) consequence else alternative  Examples if (x == 1) y = 2; if (x == 1) { y = 2; z = 3; } if (x == 1) y = 3; else y = 4;

7/1/09Harry Howard, CPST 410, Tulane University22 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.

7/1/09Harry Howard, CPST 410, Tulane University23 MoveTilTouch.nxc task main() { OnFwd(OUT_AC, 50); if (Sensor(S1) == 1) { Off(OUT_AC); }

7/1/09Harry Howard, CPST 410, Tulane University24 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.

7/1/09Harry Howard, CPST 410, Tulane University25 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

7/1/09Harry Howard, CPST 410, Tulane University27 How would you do this?  TRIBOT, display the output of the Light sensor briefly (500ms) 10 times.

7/1/09Harry Howard, CPST 410, Tulane University28 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.

7/1/09Harry Howard, CPST 410, Tulane University29 Go ahead and do it  TRIBOT, display the output of the Light sensor briefly (1s) 10 times.

7/1/09Harry Howard, CPST 410, Tulane University30 DisplaySensorLoop.rbt

Loops in NXC

7/1/09Harry Howard, CPST 410, Tulane University32 REPEAT  The repeat command, repeat(t) {}, repeats what is in the curly brackets for the number of times given by t.

7/1/09Harry Howard, CPST 410, Tulane University33 Convert the example to NXC  TRIBOT, display the raw output of the Light sensor briefly (1s) 10 times.

7/1/09Harry Howard, CPST 410, Tulane University34 DisplaySensorLoop.nxc int light; string text_light; task main() { repeat(10) { light = Sensor(S3); txt_light = NumToStr(light); TextOut(0, LCD_LINE4, txt_light); Wait(1000); }

More practice Program 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!

7/1/09Harry Howard, CPST 410, Tulane University36 Follow up  TRIBOT, display the output of the Light sensor briefly (1s) 10 times and beep after each display. Laugh when you are finished.

7/1/09Harry Howard, CPST 410, Tulane University37 SensorLoopSound.rbt

7/1/09Harry Howard, CPST 410, Tulane University38 SensorLoopSound.nxc int 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); }

7/1/09Harry Howard, CPST 410, Tulane University39 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.

7/1/09Harry Howard, CPST 410, Tulane University40 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!

7/1/09Harry Howard, CPST 410, Tulane University41 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.

7/1/09Harry Howard, CPST 410, Tulane University42 RepeatTurn.rbt

7/1/09Harry Howard, CPST 410, Tulane University43 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.

7/1/09Harry Howard, CPST 410, Tulane University44 RepeatTurn.nxc task main() { repeat(4) { OnFwd(OUT_BC, 50); Wait(500); OnRev(OUT_C, 50); Wait(650); }

7/1/09Harry Howard, CPST 410, Tulane University45 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’.

7/1/09Harry Howard, CPST 410, Tulane University46 MoveLightLoop.rbt

7/1/09Harry Howard, CPST 410, Tulane University47 MoveLightLoop.nxc task 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); }

7/1/09Harry Howard, CPST 410, Tulane University48 Next time  Quiz 1  This will just be a quiz on the blocks.  More loops, switching.  Random numbers.  'Line Follower' - project done in class