Creators: Snake

This week we looked at creating a user-steerable snake in the style of the classic phone game.


Image from James Hamilton-Martin, Flickr

Things we need

The snakes head moves and the rest of the snake’s body is made up of places the head’s already been, up to a certain point. For this we use a JavaScript array (we’ve also called it a list at times).

We don’t want the snake’s length to grow indefinitely, so we have a maximum length. Once the list of stored locations gets larger than this, we use the JavaScript splice() command to remove the first (oldest) element from the list.

Direction and turning

Screen Shot 2018-02-06 at 22.59.28

We assign numbers to represent directions on the screen. Zero is right, one is up, two is left and three is down. Note then that if the snake is heading right (in the screen sense) and turns left it goes to up (in the screen sense); direction goes from zero to one. Similarly, if going up (in the screen sense) and it turns left then it goes to left (in the screen sense).

Generally then we note that turning to the left makes the direction number get bigger while turning to the right makes it get smaller. This rule hold until we get to a number bigger than three or smaller than zero; these make no sense. If direction is at zero and the snake goes right, we set direction to three. Similarly, if direction is at three and we turn left, we set direction to zero.

Getting this week’s code

As always, all the code from our Creator group can be found on our GitHub repository.

Hackers – Remote Controls for Our Bots!


In the Hackers group this week, we took a large step forward in our Project SABRE (Small Autonomous Battling Robotic Entities), when we started working with remote controllers for our robots.


From what the group has read, it looks like the most widely-used controllers are Spektrum-compatible DSMX or DSM2 ones. Therefore, we bought 3x Lemon RX DSMX/DSM2 receivers and one MLP4DSM Blade transmitter (as shown in the photo).

Connecting to the Arduino

Pins on the receiver are simply connected to digital pins on the Arduino.

To program the Arduino to read the receiver, this code has been cross-referenced from other forums:

According to the comments, while this works, you should use interrupt-driven code.

This StackExchange post has a good list of possible references:

There was a lot of excitement when people were able move the joystick on the transmitter and have it change the value being printed out in the Arduino console!

Creators: Spirograph

This week in the Creators group we looked at emulating the classic toy, the Spirograph.


The Spirograph consists of geared plastic discs. One disc is fixed in place over a sheet of paper and the other, with a pencil tracing the path, is allowed to spin around it. The result is a complex and beautiful design on the paper.

Screen Shot 2018-01-30 at 17.04.14

This diagram should help explain in conjunction with the photo. The centre of the black disc spins around the centre of the red disc, which itself doesn’t move. So the centre of the black disc rotates around in a circle. Pretty simple?

Now, the pencil itself rotates around the centre of the black disc. Shouldn’t that make a circle too? Well it would if the black disc wasn’t moving. Thankfully though, it is and that’s what makes this interesting.

Finding the Location of the “Pencil”

So how do we find the location of the pencil? Let’s look at our diagram again, but with things re-labeled a bit:

Screen Shot 2018-01-30 at 17.33.58

  • Centre: Formerly “centre of red disc”. It’s the fixed centre of our spirograph
  • Centre2: Formerly “centre of black disk”
  • Point: The point on our curve. This is where the pencil would be in a physical spirograph.
  • Radius0: Distance from Centre to Centre2
  • Radius1:Distance from Centre2 to Point
  • Angle0: The current angle of the line between Centre and Centre2
  • Speed0: The amount that angle0 increases every time we draw
  • Angle1: The current angle of the line between Centre2 and Point
  • Speed1: The amount that angle1 increases each time we draw

So at any time the location of our point is:

Point = Centre + [Centre2 relative to Centre] + [Point relative to Centre2]

So know where Centre is and if we can calculate where Centre2 is relative to Centre and similarly where Point is relative to Centre2, we can just add them all together!

Given an angle and a distance, can we get a location?

The answer to this is a resounding “yes”! Look at the diagram:

Screen Shot 2018-01-30 at 17.56.34

given an angle and a radius, we can calculate the X and Y position of any point around a circle. The magic is the COS and SIN (pronounced “kos” and “sign”) functions. These functions exist in almost all programming languages and JavaScript’s no exception.

Using p5.Vector

The last big concept we tackled thus week was using P5js’s built-in vector class to store (x, y) points and make our code tidier. To make a vector we just use createVector(x, y). We can then use functions to add them together, etc. We would get the same result working with the X and Y values separately but the code is a lot neater and shorter.

And in conclusion

This looks pretty cool:


Getting this week’s code

As aways, all the code from our Creator group can be found on our GitHub repository.


Explorers Week 9 – Paint Program

Hi everybody,

Hope you all enjoyed finishing up our drawing program. We made good use of costumes this week to make it look like we were dipping our paint brush in each of the different colours.

We also used a variable similarly to how we used in the Piano Game we made. We made it into a slider and then code select the Pen Size we wanted.

Here are the notes in PDF. CDA-S6-Week_08-Paint

See you next week for something a little Christmas themed!




Creators – Arrays and Classes

Several Values in One Place

This week we looked at two very useful concepts in JavaScript, Arrays (we’ve also called them lists) and Classes (we’ve also called them objects). They are both things that allow one variable to store more than one value at at time. This can often be very convenient and has the potential to save us a lot of typing! Who doesn’t like that?


A plain variable in JavaScript can store a single value, we’ve seen that loads of times:

let a = 5;
let b = 7;
let c = a + b; // will be 5 + 7 = 12

An array variable in JavaScript can store more than one value, just by putting them in square brackets and separating them with commas:

let a = [5, 7]
let c = a[0] + a[1]; // This is the same as above!

The code here does the exactly the same thing as the block above it. See that a now has two values in it and we use a[0] to get the first value and a[1] to get the second. This technique isn’t super useful when we only have two values, but the more we have to store, the more useful this gets. Imagine if we had 10 values,  how much shorter would the array version be?

You can also create an empty array and put values in it later:

let a = [];

In the code above we create an empty array (nothing between the square brackets) and then use the push() function to add two values into it.

Concept of Classes

A class is a programming concept that lets you define objects which contain both Properties and Methods. Properties are values associated with the object. Methods are actions that we can ask the object to perform.


Think of yourself as a Person object and imagine some of the Properties and Methods you might have.

Your Properties might include NameAgeHeightWeight, etc. A simple Method you might have could be SayHi(). That would make you say “Hi, it’s <Name>!”.

A method might have arguments, so it could be SayHiTo(“Dave”) which would make you say “Hi Dave!”.

Classes in JavaScript

Making classes in JavaScript is pretty easy. Let’s look at the Person class we showed above:

class Person{
  constructor(name, age, height, weight){
   this.Name = name; 
   this.Age = age; 
   this.Height = height; 
   this.Weight = weight;
    Console.Log("Hi, it's " + this.Name + "!");

     Console.Log("Hi " + who + "!" );

We say “class“, the name of the class and a pair of curly brackets. Inside these brackets we have three functions (but notice we don’t have to say “function“).

Let’s look at the first of these, called constructor(). This is where we set the class properties. Note that we must put “this.” before properties to distinguish them.

The second two functions, SayHi() and SayHiTo() aren’t too usual, again note that we must use “this.Name” to get the value of the name property.


This week we created a class to represent a bouncing ball and we saw how easy it was, once we’d created the class, to make several of them, all bouncing around simultaneously. This would have taken us a lot more code to do if we hadn’t made a class. As always, the files can be downloaded from our Github page.







Creators – Being Random

Screen Shot 2017-10-17 at 00.56.49

This week we mainly looked at three things:

  • How data is organised on your computer
  • Creating functions
  • Using randomness to make things interesting

Data Organisation

Most of us had heard of a hard-disk before. This is a stack of metal disks inside your computer. Each metal disk has a special coating made of millions of tiny magnets (like you might find stuck to the fridge) that can be turned on and off.11644419853_9499fa0faa_b

We saw that able to turn something on and off, like a switch, was enough to count from zero to one, but the more switches we added, the higher we could count. Two switches can count from zero to three:

Switch 1          | Switch 2          | Total (Add)
[Off = 0, On = 1] | [Off = 0, On = 2] |
Off = 0           | Off = 0           | 0
On  = 1           | Off = 0           | 1
Off = 0           | On  = 2           | 2
On  = 1           | On  = 2           | 3

With enough of these tiny switches, we can store anything we need. Each of these tiny switches is also known as a ‘bit’ and a 1 terabyte hard disk has a billion of them!

We also saw that the files on your disk are arranged with folders (also known as directories). Folders can contain both files and more folders. This allow us to keep our hard disk organised; without them all our files would be in the same place which would be difficult once we had more than a few. The location of a file is called its “path”. Looking at the highlighted file on the desktop of my Mac we can see the full path would be:

Screen Shot 2017-10-16 at 22.19.59

/Users/kierancoughlan/Desktop/Ball and Bat Sounds.m4a


This means that, reading backwards, the file called ‘Bat and Ball Sounds.m4a’ is in a folder called ‘Desktop’ which is itself inside a folder called ‘kierancoughlan’ which is, at the highest level, inside a folder called ‘Users’.


A function is a collection of commands that do a job together. We’ve already encountered them, even if you hadn’t especially noticed:

  • Our P5 template already contains two functions called start() and draw()
  • All of the P5 commands we have used, such as createCanvas() and rect() are functions themselves

We could add all our code to start() and draw(), in fact, that’s what we’ve done before this week. That’s fine starting out, but it does mean, once there are a lot of commands in those functions, that our code is gets harder to read and understand. Breaking out a few commands into a new function and giving it a name that describes what it is doing, really helps.

Once we’ve written a function, it can be called as many times, and from as many places, we as need.

Functions can do one other thing too: they can give back a value to the place where they were called from. For this we use the special word return. For example, let’s see what a function to pick the largest of two numbers, we’ll call it Max(), might look like:

function start(){
    let a = 4;
    let b = 10;
    let c = Max(a, b);

function Max(n1, n2){
    if (n1 > n2)
        return n1;
        return n2;

We give Max() the two numbers we are comparing. If the first one is bigger than the second, it gives back the first. Otherwise, if gives back the second. Note too that the names of the variables in Max() are different to those in start(), and that’s not a problem.


Finally, we looked at the P5 function random(). We used it two different ways:

random(); // gives a number between 0...1
random(n); // gives a number between 0...n (where n is a number!)

In the first form, we used it to pick a random colour. In the second, we used it to pick a random position for our squares.


As usual, all the code is on the creators github repository. Head there and download it!! The files for this week contain both the script we wrote (sketch.js) and a longer version that I wrote (sketch2.js). Feel free to take a look at both!

CoderDojo Athenry Returns on 16 September 2017!


CoderDojo Athenry is re-starting after the summer!

We will have an information session for new and existing members on Saturday 16 September 2017 at 12:00 in our usual venue, Clarin College Athenry (formerly known as “the Tech”). Usual sessions will resume the week after, on Saturdays at 12:00.

We hope you can join us. You are welcome to invite your friends along too!

New members are always welcome. To join, just come along on the first day and fill out a registration form. Young people aged 12 and under have to be accompanied by a parent/guardian for the whole session.

And don’t forget, CoderDojo Athenry is run by volunteers and is completely free for participants — no membership fees, no weekly contributions. You should bring a laptop if you have one, but we have some loaner laptops if you don’t. There is more information on our About page.

Creators: Text Based Adventure

The last two weeks we were looking at something quite different: a text-based adventure system built in Unity. This was inspired by the Henry Stickmin games and also by the old 80s-style choose-your-own-adventure books.


Basic Program Design (Story Card)

The user is presented with a “story card”. A card consists of some text describing their current situation and (normally) a number of options to choose from.

Screen Shot 2017-04-05 at 14.12.23.png

Depending on which option they pick, the story branches from there, card-by-card, until it reaches an end (a card with no options).

Setting up a card is straightforward:

Screen Shot 2017-04-05 at 14.15.27.png

You enter the card description (the text the user sees on screen), the text that the user will see on each option button (the program supports up to four at the moment) and the card (or branch, but we’ll get to that later) to jump to when that option is selected.

There’s also the mention of “States to Set True/False” and we’ll explain that next.

Story States & Story Branches

We could have programmed the system entirely using only cards, but there’s one situation where this becomes tedious. Imagine that you have a choice; hitting a button for example. The consequences of this choice won’t become apparent until later in the story. If we only had story cards, then we’d have to branch the story immediately at his point, replicating the same steps on both branches until the point at which the consequences of your action played out.

Fortunately, there is a better way.

First, to remember the value we introduce the idea of a “story state’. It’s just a container for a true or false value. Cards can set the value of specific states when they are activated as seen above.

Screen Shot 2017-04-05 at 14.14.09

So, that covers remembering values, how do we then make use of them? This requires a “story branch”. A branch references a state and two places for the story to go (either of these can be a card or another branch). The value of the state determines which is picked.

Screen Shot 2017-04-05 at 14.19.01


Game Manager

This class looks after the story. It is responsible for updating the UI to the details of the current card, for handling the use clicking on specific buttons and generally directing the flow of the story. It also needs a StoryCard to start off the story with.

Screen Shot 2017-04-05 at 14.21.33.png



The project, including a very simple story using a number of cards and also a couple of states, can be found here. There are two scenes in the project, Adventure which contain a simple story and Basic which is a good starting place for your own story.