Team California Instruments: Priscilla Cheng, Tony Abdo, Rahul Ramakrishnan

Published August 1, 2015

Back to the Drawing Board!

Plug in the board, connect any drawing utensil of your choice, draw paper of your choice, and save your masterpiece digitally!

IntermediateFull instructions provided2,431

Things used in this project

Hardware components

10-turn linear potentiometer (10k)

Momentary switch

LED (generic)

BeagleBoard.org BeagleBone Black

Structural bracket

Retractable badgeholder

Spool

Resistor 1k ohm

100 kΩ Resistor

Hand tools and fabrication machines

Drill press

Jigsaw

Hand drill

Vice

File

Story

We all know how hard MS Paint is to use.

Drawing on a computer can't match the ease and accuracy of moving around a pencil on paper in real life. A mouse or trackpad is far too cumbersome to maneuver, making even a stick figure hard to look good. But what if there was a way to map actual pencil strokes onto the computer so that you could still draw naturally AND have your creation on your screen? This is why we made Back to the Drawing Board!, a simple way to use a pen or pencil and draw on actual paper which translates your drawing on to a screen.

Back to the Drawing Board! works by having two potentiometers that change voltage when pulled on. These voltages from the potentiometers are mapped to x and y coordinates on a canvas that draw the image. The setup for the string potentiometer was created from scratch by us.

The user first sets up the apparatus by placing a paper on the drawing board and then inserting a pencil into the washer. Next, the user presses and holds the draw button the breadboard to activate the draw function. This allows for the user to move the pencil continuously and draw whatever curves they wish. To stop drawing, just release the button and move the pencil to the next desired location.

There is also a button to toggle through various colors to create more vibrant works of art.

We utilized processing.js library to handle graphical functions like draw() and used BoneScript library to read the voltages from the BeagleBone.

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Code

Main Code

<html>
  <head>
    <script src = "processing.js"></script>
    <script src = "bonescript.js"></script>
  </head>
<body>

<canvas id="sketch"></canvas>
  
<script id = "script1" type  = "text/javascript">
(function() {  
  
  var canvas = document.getElementById('sketch');
  var pjs = new Processing(canvas);
  
  var LED = "P9_15";
  var BUTTON = "P9_11";
  var COLORBUTTON = "P9_13";  
  var X_POT = "P9_33";
  var Y_POT = "P9_35";
  
  
  setTargetAddress('192.168.7.2', {initialized: run});
  
  //set up bonescript
  function run() 
  {
    var b = require('bonescript');
    b.pinMode(BUTTON, b.INPUT);
    b.pinMode(COLORBUTTON, b.INPUT);
    b.pinMode(LED, b.OUTPUT);
    b.pinMode(X_POT, b.INPUT);
    b.pinMode(Y_POT, b.INPUT);
    b.digitalWrite(LED, b.LOW);

    //canvas setup
    var drawPoint = false;
    var black = pjs.color(0,0,0);
    var red = pjs.color(255,0,0);
    var green = pjs.color(0,255,0);
    var blue = pjs.color(0,0,255);
    var currentColor = black;
    var COLORS = new Array(blue, green,red, black);
    var colorIndex = 0;
      var iterations = 0;
    

    //board and drawing functionality setup
    var drawMode = false;
    var startNewLine = true;
    var xcoord = 0;
    var ycoord = 0;
    var prev_xcoord = 0;
    var prev_ycoord = 0;
    var xmin = 0.15;
    var ymin = 0.15;
    var xmax = 0.95;
    var ymax = 0.95;
    var xraw = 0;
    var yraw = 0;
    var board_width = 0;
    var board_height = 0;
    var canvas_width = 512;
    var canvas_height = 512;


    pjs.setup = function()
    {

      pjs.size(canvas_width,canvas_height);
      pjs.background(240);
      pjs.fill(black);
      pjs.rect(450,450,62,62);
      pjs.fill(red);
      pjs.rect(450,388,62,62);
      pjs.fill(green);
      pjs.rect(450,326,62,62);
      pjs.fill(blue);
      pjs.rect(450,264,62,62);

    };
    
    pjs.draw = function()
    {
     
      if (pjs.keyPressed==true)
      {
        if (pjs.key=='c' || pjs.key=='C')
        {
          pjs.setup();
        }
      }

      b.digitalRead(BUTTON, onButtonPress);
        if (iterations >20)
        {
            b.digitalRead(COLORBUTTON, onColorSwitch);
            iterations = 0;
        }
        else{
            iterations++;
        }

      if (drawMode==true && xcoord < 450)
      {
        pjs.strokeWeight(2);
        pjs.stroke(currentColor);
        pjs.beginShape(pjs.LINES);
        pjs.vertex(prev_xcoord, prev_ycoord);
        pjs.vertex(xcoord, ycoord);
        prev_xcoord = xcoord;
        prev_ycoord = ycoord;
          pjs.endShape();

      }
    }
    
    function onColorSwitch(y)
      {
         console.log(colorIndex)
         if(y.value==b.LOW)
        {
            console.log("low")
            if(colorIndex == COLORS.length-1)
            {
                colorIndex = 0;
            }
            else
            {
                console.log("in increment")
                colorIndex ++;
            }
            switch (colorIndex)
            {
                case 0:
                                    console.log("in 0")

                    currentColor = COLORS[0];
                    break;
                case 1:
                                    console.log("in 1")

                    currentColor=COLORS[1];
                    
                    break;
                case 2:
                                    console.log("in 2")

                    currentColor = COLORS[2];
                    break;
                case 3:
                                    console.log("in 3")

                    currentColor = COLORS[3];
                    break;
            }
        }
        
      }
    


    //determine how to handle button HIGH vs button LOW
    function onButtonPress(x)
    {    
         var temp = voltageToCoords()
      if (x.value==b.LOW)
      {
        b.digitalWrite(LED, b.HIGH);  //turn on indicator LED

        if (temp ==false)
        {
          drawMode = false;
          return;            
        }
        if (startNewLine==true)
        {
          //sleep(200);
          prev_xcoord = xcoord;
          prev_ycoord = ycoord;
          startNewLine = false;       //currently drawing this line, so set to false
        }

        //select a color
        if (xcoord > 450 && xcoord < 512 && ycoord > 264 && ycoord < 326)
          currentColor = blue;
        if (xcoord > 450 && xcoord < 512 && ycoord > 326 && ycoord < 388)
          currentColor = green;
        if (xcoord > 450 && xcoord < 512 && ycoord > 388 && ycoord < 450)
          currentColor = red;
        if (xcoord > 450 && xcoord < 512 && ycoord > 450 && ycoord < 512)
          currentColor = black;
        drawMode = true;
      }
      else
      {
        drawMode = false;           //turn off drawing mode
        b.digitalWrite(LED, b.LOW); //turn off indicator LED
        startNewLine = true;        //get ready to start new line
      }
    }

    function voltageToCoords()
    {
      b.analogRead(X_POT, readX);
      function readX(x) 
      { 
        xraw = x.value;
      }
      b.analogRead(Y_POT, readY);
      function readY(y) 
      { 
        yraw = y.value;
      }
      xcoord = ((xraw - xmin) / (xmax - xmin)) * canvas_width;
      ycoord = ((yraw - ymin) / (ymax - ymin)) * canvas_height;

      if (xcoord < 0 || ycoord < 0)
        return false;
    }
    function sleep(milliseconds)
    {
      var start = new Date().getTime();
      for (var i=0; i<1e7; i++)
      {
        if ((new Date().getTime() - start) > milliseconds)
          break;    
      }
    }

    pjs.setup();
    pjs.draw();
    pjs.loop();

}
})(); 

</script>
</body>
</html>

Back to the Drawing Board!

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Schematics