# Arduino makes 2D Level

This is a project for Arduino to make a 2D Level, aimed at beginners.

Arduino draws a circle on an LED Matrix that moves around according to readings from a 2D Accelerometer.

Objectives:
* Learn how to draw a circle using simple Math’s
* Learn how to use the LOL shield for the Arduino
* Learn how an accelerometer works

## Step 1: What you need

You will need:
* Arduino UNO
* LOL shield   (http://jimmieprodgers.com/kits/lolshield/)
* Breadboard for wiring up e.g. (http://www.oomlout.co.uk/prototyping-bundle-for-arduino-ardp-p-186.html)
* Some Wires

## Step 2: Wire it up

Attach the LOL shield to the Arduino.

Wire the Accelerometer as follows:
+3V
GND
X => A0
Y => A1
Z => N/C  (Not Connected)

Note: The LOL shield does not come with Headers (as shown in the picture), attached to the topside.

I bought some here: http://www.amazon.co.uk/gp/product/B004RASBVY/ref=oh_details_o06_s00_i00

## Step 3: Install the LOL Shield Libraries

Install the Arduino libraries for the LOL shield if you don’t have them already. You can get the link to them from this page:
http://jimmieprodgers.com/kits/lolshield/

We’ll start by drawing a circle.

This circle will eventually move around as we tilt the device. But first things first….

We’ll illuminate individual pixels on the LOL shield using the LOL library command:

LedSign::Set(x, y , 1);

where x and y are the coordinates on the shield of the LED we wish to illuminate

Our job is to figure out how to calculate the x,y  values that make a circle.

In Pseudo code we do it like this to draw just one quarter (Quadrant) of the circle:

for x = 0 to RADIUS
y=f(x);     // This means y is some function of x. We haven’t said what function yet
plot(x,y)
end

So what’s the function?

r^2 = x^2 + y^2

where x^2 means “x squared” or “x to the power of 2”

We know x because it’s the for loop iterator;
We know r because it’s the radius,
So we re-arrange to find y

y = sqrt(r^2 – x^2)    // sqrt() means square-root

When you code it up you get a circle as shown in the picture.

## Step 5: Here’s the Code

Here’s the Arduino code to draw the circle.

Notice that the circle is drawn in 4 quadrants. We illuminate 4 LEDs for each y we calculate.

The pictures show the steps to draw the circle as x iterates from 0 to RADIUS

#include <Charliplexing.h>

// Circle: radius, inital and max x/y values
int cx = 6;        // x-position of circle
int cy = 4;        // y-position of circle

void setup()
{
Serial.begin(9600);
LedSign::Init();
}

void loop()
{
DrawCircle(1);      // DRAW the circle
}

void DrawCircle(int ink)
// ink =0 : ERASE the circle
// ink =1 : DRAW the circle
{
for(int x = 0; x <= radius; x++)    // x values from 0 to RADIUS (one Quadrant)
{
// solve r^2 = x^2 + y^2 for y
float y = sqrt(pow(radius, 2) – pow(x, 2));
y = round(y*1);
// Fill the y-position in the 4 quadrants of the circle
LedSign::Set(x + cx, y + cy, ink);    // Quadrant 1
LedSign::Set(x + cx, cy – y, ink);    // Quadrant 4
LedSign::Set(cx – x, y + cy, ink);    // Quadrant 2
LedSign::Set(cx – x, cy – y, ink);    // Quadrant 3
}

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