Sunday, 22 December 2013

Getting Started


Many parents tend to freak out whenever “computing” or “programming” subject is brought up, and too often, it’s their own fear that limit themselves or their children the broader uptake in technologies.   

Technology has evolved since the dawn of smartphones. Gone are the days where it takes a person conversant in electronics to build an alarm clock.  With today’s advancement, a micro-controller and a display, with a little programming skill is all it takes to achieve that task. With Scratch, as a block based programming tool, there’s nothing easier than snapping the blocks together.

By the way, Scratch comes in 2 version. The latest version being Scratch 2.0, and the older version is Scratch 1.4. As mentioned earlier, other than interactive programming with Scratch, Arduino micro controller will be included to get things “physical”. The only stable derivative that I’ve tried so far is S4A, a Scratch 1.4 extension. Hence, throughout my blog, I’ll stick to Scratch 1.4 and S4A.

Download Scratch 1.4 at http://scratch.mit.edu/scratch_1.4/


Start Scratch 1.4 once you have completed the installation. The interface should look something like below :























Make something move

On the Stage area, a default  image of a cat is loaded whenever Scratch is started. You can import or create as many images as you like, and each image is assigned a name Sprite1, Sprite2 etc. All the sprites are visible on the Sprite Thumbnail area.


Drag the “move (10) steps” block to the Script Area as shown below :


As the name implies, it moves a sprite 10 steps whenever it is activated. The number of “steps” represent each pixel on the computer screen. Try exploring the “move” block by clicking it with your mouse pointer and change the steps with different number. The sprite should move accordingly to the steps when the “move” block is clicked.
You can drag the sprite to anywhere on the Stage Area, which is 360 x 480 pixels wide, as shown below.



The sprite position is shown right above the Script Area, next to the sprite image :
Try to drag the sprite anywhere the Script Area, the sprite position changes accordingly.



Let’s create a building block, making the sprite move back and forth around the Stage Area. The program has to meet the following criteria :

  1. Program starts upon clicking the "when clicked" block or the "Green Flag" button.


  1. The sprite starts moving at position x = 0, y = 0 at the beginning of the program.
  2. When the sprite hits the edge of the screen, turns back and move to the other end of the screen.

Let’s follow the above criteria  “sequentially”.

Criteria(1) - Click on the “Control” button from the Pallete Block. Drag the block as shown below


Criteria (2) –The sprite starts at position x= 0, y = 0 the minute "when clicked" block  is clicked irrespective of where the sprite is. , then move 10 steps continuously. 

Click on the “Motion” button and drag "go to x:() y:()block to the Script Area







Snap the  "when clickedand "go to x:() y:()"   blocks together. It should look something like below




Drag the "move() steps" block and snap it below  "go to x:() y:()block.

Criteria (3) – The sprite turns back when it hits the edge of the screen.
We have to look for a block that does the job.  On the “Motion” button, scroll down the list of blocks and try to locate "if on edge, bounce" block. Snap it to below the "move() stepsblock.

By now, your script should resemble below 


Are we ready to go ??? 
Let’s analyse the script before we begin. It is worth noting that the script executes each block (instruction) “sequentially” once at a time and it looks something like below in “flow chart” terminology.

When the "if on edge, bounce"  block is executed, it just stops there as there are no other instructions to follow, and we want the sprite to move continuously. To get around it, the solution is to create a loop so that it “repeats” the operation after the "if on edge, bounceblock. 


To create a loop based on the above flow chart, drag the "foreverblock to the Script Area and insert the  "if on edge, bounceand "move() stepsinto the “forever” block. Your script should look something like below


That looks more sensible. Now, click on the  "when clicked" or the "green" flag on the top right  to start the program.

You will note the following :

  1. The sprite moves very fast. 
  2. When the sprite hits the right edge, it “bounced” back moving to the left direction upside down

While the sprite is still moving, slow down the speed by inserting the "wait () secs block as shown below


The sprite now moves 10 steps every 1 sec and this is too slow. Change the delay from 1 sec to 0.2 sec, or any value at your comfort.

Next, click on the “left-right” button as shown below




That should fix the “upside down” position of the sprite.

Somehow, something is still missing. The sprite doesn’t look vibrant, and we need to add a little “spice” to  the script with some animation

Under the “Looks” button, click on the “Costumes” tab



You will see two costumes, namely Costume1 and Costume2.

Note : Each sprite can have multiple costumes, either created by yourself or imported from the built-in library. You can have as many sprites as you like.

Imagine if the costume of the sprite switches each time it moves, doesn’t it give a bit of zing to the sprite ??

Return to the Script Area by clicking on the “Scripts” tab a show below.


Click on the “Looks” button, and insert the "next costumeright below the "move() stepsblock.


Your script now should look like below


By now, the sprite should look more vibrant, “walking” back and forth the Stage Area.

Here's a good video tutorial http://www.youtube.com/watch?v=pkhjX792yVI to help you started.