mblock Robotics Advanced Programs

Transcription

1 mblock Robotics Advanced Programs Computer Science Unit Activity 1 - Changing Colors with Variables Each LED has 3 different lights Red, Green and Blue all of which can be assigned a value between 0 and 255. The variety of the colors that can be attained using these primary colors is displayed in this color wheel: In this tutorial, I want to display all the colors in this wheel on the robots LEDs. Have a think about what the pseudocode is going to be. Let s start with the lights set to all blue and go clockwise round the wheel (so towards green). As we go around, we need to reduce the level of the blue and increase the level of the green: Set LED to blue. Repeat until fully green: ---- level of blue Increase level of green. This is the start of the code. However, there is a problem. Once the LED has been set, we cannot read the levels of green and blue. So on the next loop, how do we know what to set the LEDs to? We need a variable. Variables are places to store information. In mblock, variables store numbers. Each variable is given a name. The name should be chosen to reflect what kind of information the variable holds. So, for my tutorial today, I am going to have 3 variables: redsetting greensetting bluesetting

2 A common naming convention is for variables to be all one word (no spaces) with the first letter being lower case and all subsequent words first letter being upper case. To make a variable in mblock, we need to go to the Data&Blocks script and choose Make A Variable : When you press the button, it will ask you for a name: Make sure you choose a name that describes the information that the variable will hold. Once you have defined a variable, it will display some blocks related to the variable that you can use for programming:

3 Unless variables are going to be changed early on in a program, it is considered good practice to initialize variables at the start of a program. For my program, I want to start with blue turned on, and green and red turned off. I am going to turn the LEDs on up to a maximum value of 100: And now I want to set the LEDs to the values of these variables: Now I want to decrease the blue setting one-by-one until I get to zero. At the same time, I want to increase the green setting until that gets to 100. So I will need to repeat this step 100 times: Challenge: 1. Can you finish the program so the LEDs continue to fade through the colors in the color wheel? 2. Can you write a program that measures the light (using the on-board light sensor) as the LEDs fade? What LED settings provide the darkest measurements? Write down any problems you face as you write this program. How did you solve the problems? Construct Your Dreams!

4 Activity 2 - The On-board Button and the Timer Computer Science Unit In this tutorial, I would like to introduce the on-board button and the timer. The onboard button has 2 related programming blocks in mblock. The first one is a header block: This can be used as a trigger for some code to be run. NOTE: this block can only be used when running programs from the mblock environment. The second block is a Boolean block. A Boolean block is one which can be used in a conditional (like if ) and will return either true or false: The drop-down menus for both blocks are either pressed or released. There are two timers in mblock one runs within the mblock environment, and the other runs on the board. Therefore which timer you use should depend on where you intend to run the program. The mblock environment timer blocks can be found in the Sensing scripts: The robot timer blocks can be found in the Robots scripts. We can use the reset timer block to set the timer to zero: Once the timer is reset to zero, it will begin counting immediately. You can later access how much time has elapsed since you reset the timer by using this block: In this simple program, pushing the on-board button resets the timer and the proceeding loop is run until the timer exceed 10 seconds.

5 In this example, the effect is that the robot will run forward for a speed of 10 seconds. You may be thinking Why not just turn the motors on at speed 100, wait for 10 seconds, and then turn them off?. And you would be right. In this case, it would have the same effect. But what if you wanted to have a variable speed? Challenge: 1. Can you write a program that turns the LEDs on, and then times how long it takes someone to press the on-board button, displaying that time in the mblock environment? 2. Can you write a program that counts how many times the spacebar is pressed in 5 seconds, and displays that number in the mblock environment? 3. Can you write a program that has the mbot moving at variable speeds for 10 seconds? Construct Your Dreams!

6 Activity 3 - Line Counting Computer Science Unit The line follower sensor is usually used to follow a line, but in this lesson we are going to learn how it can be used to count lines instead. For this we are going to need a variable to count with. What other things do we need in the program? Write down some pseudocode before moving on. Declare a variable. Move forward. Loop: ---- If we see a line Add one to the variable. End Loop At the end of this program, the number of lines that the mbot passed over should be held in the variable. We can write this in mblock code. I decided to move forward and count lines for 10 seconds: There are 2 problems with this code at the moment. The first one is that there is no way to read the count variable. Read the challenges and see if you can identify and solve the second problem. Challenge: 1. Add a way to be able to verify the value of the variable. 2. With this code, the value of the variable recorded will not be correct. Can you figure out why? And how to correct this? Construct Your Dreams!

7 Activity 4 - Writing the Default Program with Functions (Blocks) Computer Science Unit Different sections of a program often do different things. A program can be divided up into separate parts with each part performing a particular function. From the main program, these functions can be called or run. This makes the code much more readable. In mblock, we make a function (or block) by clicking on Make a Block in the Data&Blocks script: Then choose a name that represents what the block is doing: And then the block is defined and ready to use. So in this tutorial I want to recreate the default program. It will be a close approximation to the default program though, not a complete replica. First, the robot initializes with the beeps and lights:

8 I am going to put this into its own initialization block and call it from the mbot program: This now runs exactly the same as if the set LED commands and the play tone commands were called directly from the mbot program. The code is much easier to read like this though. Next, I want to write the code for the remote control part. Again, I am going to write this code in its own block:

9 I then write similar blocks for a line following behavior and an object avoidance behavior. Now, I have to write these behaviors into my main program. As you can see, the final program looks very simple: Challenge:

10 1. Can you write programs for the Object Avoidance and Line Following functions and add them to the program? 2. Sometimes when the button is pressed, a mode or 2 is skipped. Can you fix this bug? 3. How close to the real Default Program can you make your program? Construct Your Dreams!

11 Activity 5 - Object Avoidance with Functions and Parameters Functions are a useful feature to make your code easy to read and well-organized. The real power of functions comes with parameters though. In this tutorial, we will explore that power by re-writing the object avoidance program using functions and parameters. This is the original object avoidance code: I am going to now put that code in a new function (New Block):

12 I can call the function with the objectavoidance block at the bottom of the picture above. Now what if I wanted to run this code, but instead of a motor speed of 100, I want 200? Or 150? Or 255? This is where parameters come in. A parameter allows a value to be passed to the function. To pass a parameter in mblock, you need to either create them when you create the function or after you ve created your function, right-click on any of the function blocks and select edit : Then go into Options :

13 This is where you can add parameters. When you add a parameter, you need to specify the type of parameter: number, string or Boolean. A number is just a number, a string can be numbers or letters and Boolean is either true or false. In my example, I want my function to run the program with different motor speeds. As motor speeds are a number, I will choose to Add number input. As you can see this creates a new input (parameter) in the block at the top. It names it number1, but as this will represent the speed in my program, I am going to change the name to speed : Now, when I press ok, the function has the parameter in its definition block:

14 And its call block: The only thing that remains for us to do is use the speed parameter when we set the speed of the motors. We can do this by dragging and dropping the speed parameter from the objectavoidance definition block into the places where we set the speed. The final function looks like this: At the bottom you can see the objectavoidance function is called and it passes in a speed of 125. Challenges: 1. Pass in different values of speeds and fun this function. 2. Add another parameter that controls the direction of the turn 0 for left, 1 for right, 2 for random. 3. Write another program that uses functions and parameters. Construct Your Dreams!