Scratch Advanced – Week 3 – Cryptography

Hope everyone enjoyed last week.

This week we began a series of sessions on Cryptography. We began by demonstrating why we might use Cryptography. What is Cyrptography

What created a Scratch project to Encrypt a single word or sentence using a Reverse Cipher. Notes for this Scratch project are at: Scratch Project Notes (Reverse Cipher)

We then improved the Scratch project to Decrypt the same word or sentence back to its original form.

We discussed the limitations of a Reverse Cipher and began the introduction of the next session where we will be creating a Scratch program to Encrypt and Decrypt a word or sentence using one of the most famous ciphers the “Caesar Cipher”. Named after the Roman figure Julius Caesar.

Scratch Advanced – Week 1 – Calculator.

Hi all and welcome back to what we hope will be an exciting year in Coder Dojo Athenry.

We will be using Scratch 2 this year. So the first thing that we need to do is install it.

There are two Applications that you need to install:

1. AdobeAir

2. Scratch2

I will have all the Versions that I can find on USB, which should cover both Windows and Mac. I have installed the Windows version, so I know that one works. I won’t have tested the Mac version though.

Scratch2 introduces the idea of making your own Blocks of code that you can then use in your programs. So for the first week we are going to try these out and see how they can help us write Code once but use it many times.

And for that we need a project to work on – A Calculator.

  • We will learn about Functions (Code Blocks in Scratch2)
  • We will learn about passing information into Functions

We are going to design and build a fully functioning Calculator that can Add, Subtract, Multiply and Divide. If you get really adventurous you can add some other functions as well – percentages maybe?

Like you I haven’t written it yet, so it going to be a bit scary tomorrow as we have to make it all up as we go along, but hey, you’re the advanced crowd, and should be able to handle that!

Once we have a fully working version I will update this blog with the full details of how and why we did what we did.

If we can get anything like the following picture, I think we are definitely Advanced…


Everything that you see on this calculator is perfectly possible in Scratch2, we will start with the four basic options of Addition, Subtraction, Multiplication and Division.

Countdown to Pizza!


We have just a  few weeks left before we finish up in CoderDojo Athenry for the summer.

Here is a reminder of our upcoming schedule:

  • On 18 and 25 May, ninjas continue to work on solo/group projects towards earning belts/certs, with the support of the mentors
  • On 1 June, we won’t be open for the bank holiday weekend
  • 8 June will be our final week: we will award belts/certificates for your projects, and we will have pizza for everybody!

After that, we will close for the summer and resume in the Autumn.

Scratch Intermediate & Advanced Challenge 18: Start work on your own project!


This week, we started work on multi-week projects!

The goal will be to design and implement your own project, with the support of the mentors, to demonstrate the skills you have acquired over the past few months.

In a few weeks, everyone will get to demo their projects and work towards earning:

  • Yellow certificates: for ninjas who already have a yellow Scratch belt and demo a project using those skills
  • Blue certificates: for ninjas who already have a blue Scratch belt and demo a project using those skills
  • Yellow belts and white belts: only for ninjas who do not already have a belt.

As we discussed, there are also a couple of international CoderDojo contests coming up – discuss with your parents whether you would like to enter.

Here are my notes from the day (PDF): CDA-S2-Challenge18-YourProject.pdf

As usual, get in touch on Twitter or in the comments if you would like the PowerPoint version of the notes.

Scratch Intermediate & Advanced Challenge 17: Learn about Painting!


This week, Martha led a great session in which she showed  the ninjas how to use a painting program. There are of course lots of reasons why this is useful for coding:

  • For animation, as we have been working on in recent weeks
  • For graphics for websites, including logo design as the HTML group are working on
  • For buttons, icons, and other graphics in other apps and programs

The specific program that Martha used is Paint.NET. This is free (though not open-source) and is pretty easy to use, while being quite a bit more advanced than either the Paint editor in Scratch or Microsoft Paint that is installed in Windows by default.

You can download Paint.NET here:

Paint.NET works on Windows only:  if you have a Linux or Mac laptop, many of the same functions are available in other painting packages, and the mentors will help you bridge the gap. One good alternative is Pinta Paint, which is multi-platform and its functionality is based on that of Paint.NET.

Here are the notes from the day (PDF format): CDA-S2-Challenge17-LearnAboutPainting.pdf

As usual, get in touch on Twitter or in the comments if you would like the PowerPoint version of the notes.

Also this week, our ninjas demonstrated models they had built in plasticine and graphics they had created – follow this link to see them!

Scratch Intermediate & Advanced Challenge 16: Model and Animate!


(This week, we again merged our Intermediate and Advanced Scratch groups, which means that our Challenge numbering system is now a bit messed up!)

We had lots of fun in CoderDojo Athenry with this challenge, which involved:

  • Making models with plasticine (a.k.a morla or playdough)
  • Converting the physical models into digital ones, by either drawing them in a painting program or photographing them & cleaning the photos up
  • Animating the images in Scratch

Here is a link to my fairly primitive animated Scratch model: our ninjas have made much more impressive models, which we will showcase in a post soon.

Here are my notes from the day (PDF format): CDA-S2-Challenge16-ModelAndAnimate.pdf

As usual, get in touch on Twitter or in the comments if you would like the PowerPoint version of the notes.

Next week, we will extend this topic by continuing to do modelling and have ninjas demonstrate what they have made.

Scratch Advanced – Challenge 17 – Time



How do we measure it?

Why are there 60 minutes in an Hour?   Why are there 24 Hours in a Day?

Why are there 365 Days in a Year?


We have to go back in History to find out why we 60 in time quite a lot. It is thanks to the Babylonians that we have the modern day usage of 60 seconds in a minute and 60 minutes in an hour and even 360 degrees in a circle (60 x 6)

The reason that they used 60 is because it can be divided by a lot of different numbers, for example:

60 /  1 = 60

60 /  2 = 30

60 /  3 = 20

60 /  4 = 15

60 /  5 = 12

60 /  6 = 10

60 / 10 =  6

60 / 12 =  5

60 / 15 =  4

60 / 20 =  3

60 / 30 =  2

60 / 60 =  1

And for the 24 Hours in a Day, we have to thank the Egyptians who came up with that idea. They actually used 12 for Day time and 12 for Night time. But it wasn’t till a lot later that each of these 12 parts became the same length of time.

So what is a day? Well as most of you know it is the time it takes for the earth to turn round once on it’s axis.

This isn’t strictly true though  as it only takes the earth 23hr and 56 minutes to spin once, the extra four minutes are taken up by turning to face the sun properly again.

So you should strictly say that 24 hours is the time it takes the Earth to face the Sun again, when you measure from Noon on one day to Noon on the next day.

And finally 365 days in the year, again this is something that we all know, it’s the number of days that it takes for the Earth to travel once around the Sun.

We have an Experiment we can do here as well.

If the Sun is the size of a Football, how big is the Earth and how far away will it be to be in scale?

And just out of interest here are some other planets years:

Mercury 88 days

Venus 224 days

Mars 687 days

Jupiter 4331 days

Saturn 10832 days

Uranus 307999 days

Neptune 60190 days

and finally poor old Pluto 90520 days, which is roughly 248 Earth Years.

So what does all this have to do with Computers, well all Computers have a clock and calendar in them to tell the time, so we are going to build one in Scratch, this will hopefully demonstrate how something that we take for granted and don’t even think about very much can become quite complex when you try and convert it into a Computer program.

Some of the things that you will have to think about:

1. The days in each month are not the same.

2. The hour hand does two circuits of the clock, the minute and second only one before the next thing changes.

3. Leap years. This is a fun one.

4. Daylight Savings Time (DST) When does it happen and which way do the clocks go?

We will need a few Sprites:

1. Second Hand

2. Minute Hand

3. Hour Hand

4. Clock Face

5. Day of Month

6. Month

7. Year

Now for the coding. Although we think of time in 60 minutes and 12 hours, all the hands on the clock actually need to turn through 360 degrees, so it is easier to code with that in mind rather than 60 seconds for example.

So, if you have your sprites setup, you will need some variables to store the position of each hand. Once you have those, you can put the code together, something  like this to initialise all your variables:









And then as you can see I am broadcasting Start which contains the main code like this:















And for each of the hands,  something like this should be enough:


The +90 is because Scratch has 0 degrees pointing LEFT, not UP!




The full Scratch project has been uploaded to the Scratch WebSite as well, for those of you who want to cheat :).

Scratch Advanced – Week 16 – Stop Motion Animation

We are going to revisit one of the topics we did earlier in the year. Do you remember The Movies, where we had the spinning wheel looking like it was going backwards?

Well we are going to do something similar over the next couple of weeks, where we will investigate and use Stop Motion, this is the same movie making technique that the Wallace and Grommet Movies are made with.

So what are we going to learn, well, we are going ot use a lot of techniques we have used before, so it is more a case of what are we going to re-learn.

  • Broadcasts – to make our code smaller and neater
  • Variables to simplify the code, specifically local variables.
  • Speech Bubbles.
  • Program Flow, there are a lot of things that need to happen and we need them to happen in the right order.

We are going to animate The Three Little Pigs and the Big Bad Wolf.

As you know this is a little story and in stories, things happen one after the other, so that is what we need our code to do as well, there is not much point having everything running from a Green Flag, we need some way to control the flow of the Program.

First we are going to need some Sprites though.

  1. A Wolf
  2. Pig One
  3. Pig Two
  4. Pig Three
  5. Straw House
  6. Wood House
  7. Brick House

As you know my drawing skills are excellent, so I have come up with the following:


Nice aren’t they. I’m sure you can do better.

When the Story starts there is only the Wolf, One Pig and the Straw house visible, so all the others need some code under a Green Flag to get them ready, backstage, ready for when it is their turn in the story.

The Wood House for example has just a HIDE under the Green Flag, you will need to determine what each Sprite will need under a Green Flag control. Basically anything to get it ready for the story.

On to the Stop Motion Animation.

Stop Motion is where something is moved a small bit and then a picture taken and then moved another small bit and another picture taken, until the figure has moved to where it needs to be.

We are going to do something similar, where we will set up the x and y position of the Sprite in local variables and then get another piece of code to do the actual moving, this helps to make the code a little easier to read as it splits it into smaller sections.

Here is the code for example that one of Pigs uses to move to the next House


You can see how I have split it into smaller pieces and that I have used local Variables to set the x and y positions.

You will need to figure out where on the screen you want the Sprites to go and how fast you want them to go there, that will determine the numbers that you need to use when you are SETting the xPosition and yPosition variables.

As the Wolf is kind of the main Character in the Story, we control everything from his Sprite. We do one thing after another and if we need to wait for something else to happen we use a Broadcast and Wait, this will control how the code flows from the top to the Bottom.

Here is all the code for the Wolf Sprite


Now, my code is very scrappy, there are a number of BUGs that need to be sorted out, for example when Pig One moves to the Wood House and the Wolf comes over, the Speech Bubble covers the Pig, this should be changed really.

At the end of the day, you can make your Story as simple or as complex as you like, one thing that I can tell you though, is that the more time you spend on the project the better it will end up.

You can also do real Stop Motion with a Camera and Lego, you can then import the different pictures into Scratch as either Stages or Sprites.

I did one as Stages which is up on the Scratch Web Site and here is one of the Stages from it.