a digital scan of a 35mm film image of a processing sketch running on an LCD
Skip to Content

Egg Dissolve

The mechanisms class was charged with creating egg-cracking Rube Goldberg machines for the first week's assignment. Rather than breaking the egg shell through brute force, we tossed around the idea of dissolving the egg shell entirely.

Luckily there was some muriatic acid lying around the shop, so we ran a quick experiment. The shell dissolves, but it takes about 20 minutes, and what's left isn't a broken egg, but a layer of internal membrane which keeps the de-shelled egg intact. Interesting, but not well suited to the purposes of our machine-to-be, so we shelved the idea. (Maybe it was too clever by half to begin with.)

(Science music by Boards of Canada.)

January 28 2010 at 12 PM

Triangle Soup

A quick assignment for GLART, drawing an animated field of triangles.

Here’s the code:

  1.         package mika;
  2.         import java.awt.event.MouseEvent;
  3.         import javax.media.opengl.*;
  4.         import jocode.*;
  5.  
  6.         /**
  7.          * DemoBasicGeometry.java
  8.          * <P>
  9.          * Demonstrate six types of geometry using glBegin()…glEnd()
  10.          * <P>
  11.          * napier at potatoland dot org
  12.          */
  13.  
  14.         public class Week1 extends JOApp {
  15.  
  16.           // Set the mouse position in a way that’s
  17.           // useful for translating objects at 0 Z
  18.           public float screenCursorX;
  19.           public float screenCursorY;
  20.           public float tempValue;
  21.           public float sizeMult;
  22.  
  23.           /**
  24.            * Start the application, Run() initializes the OpenGL context, calls setup(),
  25.            * handles mouse and keyboard input, and calls draw() in a loop.
  26.            */
  27.           public static void main(String args[]) {
  28.             // create the app
  29.             Week1 demo = new Week1();
  30.  
  31.             // set title, window size
  32.             windowTitle = "Hello World";
  33.             displayWidth = 1440;
  34.             displayHeight = 900;
  35.  
  36.             // start running: will call init(), setup(), draw(), mouse functions
  37.             demo.run();
  38.           }
  39.  
  40.           /**
  41.            * Initialize settings. Will be called once when app starts. Called by
  42.            * JOApp.init().
  43.            */
  44.           @Override
  45.           public void setup() {
  46.             // set a background color
  47.             gl.glClearColor(0f, 0f, 0f, 1f);
  48.  
  49.             // Move over to my second monitor for testing…
  50.             // TODO Disable this IRL
  51.             frame.setLocation(-1440, 150);
  52.           }
  53.  
  54.           /**
  55.            * Render one frame. Called by the JOApp.display() callback function.
  56.            */
  57.           @Override
  58.           public void draw() {
  59.  
  60.             // Clear screen and depth buffer
  61.             gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
  62.  
  63.             // Select The Modelview Matrix (controls model orientation)
  64.             gl.glMatrixMode(GL.GL_MODELVIEW);
  65.  
  66.             gl.glEnable(GL.GL_BLEND);
  67.             gl.glBlendFunc(GL.GL_SRC0_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);
  68.             // gl.glBlendFunc(GL.GL_ONE, GL.GL_ONE);
  69.  
  70.             // Reset the Modelview matrix
  71.             // this resets the coordinate system to center of screen
  72.             gl.glLoadIdentity();
  73.  
  74.             // Where is the ‘eye’
  75.             glu.gluLookAt(0f, 0f, 10f, // eye position
  76.                 6f, 1f, 0f, // target to look at
  77.                 0f, 1f, 0f); // which way is up
  78.  
  79.             gl.glColor4f(1f, 1f, 1f, 0.5f);
  80.             // gl.glColor3f(1f, 1f, 1f); // color will affect all the following verts
  81.  
  82.             sizeMult = 3;
  83.             tempValue = (tempValue + .02f) % 1000;
  84.  
  85.             for (int i = 0; i < 200; i++) {
  86.               gl.glRotatef(tempValue, tempValue, tempValue, tempValue);
  87.  
  88.               gl.glTranslatef(.1f, .1f, .1f);
  89.  
  90.               gl.glBegin(GL.GL_TRIANGLES);
  91.               {
  92.                 gl.glVertex3f(0f, 0f, 0f); // top
  93.                 gl.glVertex3f(-0.5f * sizeMult, -1f * sizeMult, 0f); // lower left
  94.                 gl.glVertex3f(0.5f * sizeMult, -1f * sizeMult, 0f); // lower right
  95.               }
  96.               gl.glEnd();
  97.             }
  98.  
  99.             // reset vertex color to white
  100.             gl.glColor3f(1f, 1f, 1f);
  101.           }
  102.  
  103.           @Override
  104.           public void mouseMoved(MouseEvent _event) {
  105.             // Call the parent method since it actually gives us the
  106.             // Better just to copy the whole method?
  107.             super.mouseMoved(_event);
  108.             screenCursorX = cursorX / (displayWidth / 10f);
  109.             screenCursorY = cursorY / (displayHeight / 10f) - 3f;
  110.           }
  111.  
  112.         }
January 27 2010 at 3 PM

Window Drop

Video: Susan Prentiss

I spent an unreasonable portion of my childhood in the back seat of a car, staring out the window. Rainy days, in particular, allowed for one of the more confounding means of passing the time: attempting to predict and understand the movements of water drops on the window.


Attachments

January 26 2010 at 11 AM

Market Penetration

The 4 Big Myths of Profile Pictures: a straight-faced analysis of how profile pictures of various types correlate with "success" on a dating website. The text's self-help tone is a bit cheeky, but the conclusions are based on several thousand profiles worth of data, and the charts and graphs are pure gold:



January 24 2010 at 10 PM

Buzz Pot: A Variable Detent Potentiometer

In the course of developing Brain Radio with Arturo and Sofy, we saw the need for a means of tuning between an arbitrary, and potentially unstable number of channels. For the sake of context, Brain Radio is a head-mounted EEG-based broadcast system — everyone with a headset can tune into anyone else with a headset, and listen to sounds synthesized by that person's brain waves.

How, exactly, would the tuning process take place? We knew a few things:

  • We wanted to use a dial to leverage associations with radio / tuning / broadcast / analog.
  • We would need some kind of tactile feedback, since the dial would be mounted on the headset, outside of the wearer's field of view.
  • The number of available stations / channels would vary — if three people were in range, the dial would need to be able to tune to three positions. If more channels came online or dropped out, the interface would have to adapt.

What we really wanted was a potentiometer with detents, to make it easy to click-click-click from station to station. Detents also summon a tactile delight rivaled only by toggle switches and large mechanical levers. They inflate the sense of intention associated with an action: They make you feel like you know what you're doing.

The catch, of course, is that detented potentiometers have a finite number of detents, and they're set at the factory. If we bought five-detent pots and ended up with six radio channels to tune between, we were SOL. What we needed was a variable detent potentiometer.

Google turned up some shady, product-less patent filings. And the PComp list confirmed that no such device existed — and then suggested something very savvy: use something else to generate the tactile feedback. How about a vibrator motor...

So I did exactly that. A vibrator motor, some hot glue, a potentiometer, and some code all collided to create the buzz pot:

The video doesn't really communicate the physical feedback coming through the pot when channel thresholds are crossed, but in practice it works pretty well. The number of channels is easily changed in software — and the resistance range of the potentiometer is simply divided up so a given range of values represent a single channel.

For example, a three channel setting would put channel 1 between analog values 0 and 341, channel 2 between 341 and 682, and then channel 3 between 682 and 1023. When the pot passes from one channel range to the next, the microcontroller flips on the transistor controlling power to the vibrator motor for a fraction of a second, sending a mechanical buzz through the pot that lets the user feel when they've changed channels, even if they can't see what they're doing.

Development was relatively simple. Hot glue held up surprisingly well to the vibration motor.

Buzz pot motor mountedBuzz pot bottom view

The basic test configuration includes a seven-segment LED display so I could verify when the channels changed.

Buzz pot test configuration

Here's the schematic. The seven-segment display adds some complexity... it's really just for troubleshooting purposes (sending the channel status out over serial would be much simpler). Even then, a shift-register would allow for more sensible use of the Arduino's pins if this were more than a proof of concept. The TIP 120 between the Arduino and the vibration motor is definitely overkill, I just put it in place since Brain Radio was going to have discrete power sources and it would have made sense to put the motor on the non-Arduino power supply. (Some of the graphics in the schematic were adapted from the Fritzing project.)

Buzz Pot Schematic

And finally, the code:

  1. // Buzz Pot
  2. // Eric Mika, 2009
  3. // Provides tactile feedback for a potentiometer to denote changes
  4. // from one value range to another. Ideal for situations where an unknown
  5. // number of values must be set by a single potentiometer.
  6. // To do:
  7. // 1. Debounce the thresholds.
  8. // 2. Handle fringe-case runtime channel count changes.
  9.  
  10. int vibratorPin = 9; // Turns the vibration motor on and off through a transistor.
  11. int potPin = 0; // Reads the potentiometer.
  12. int potValue = 0; // Stores the potentiometer value.
  13.  
  14. int channels = 10; // Number of values selectable by the pot.
  15. int currentChannel = 0; // Starting value.
  16. int lastChannel = 0;
  17.  
  18. int vibDuration = 200; // How long to turn the motor on when thresholds are crossed.
  19. unsigned long vibStart = 0; // Keep track of time so we know when to turn off the motor.
  20.  
  21. // Map digital pins to their respective LEDs in the 7 segment display.
  22. // Could use a shift register instead to save pins.
  23. int dispA = 2;
  24. int dispB = 3;
  25. int dispC = 4;
  26. int dispD = 5;
  27. int dispE = 6;
  28. int dispF = 7;
  29. int dispG = 8;
  30.  
  31. void setup() {
  32.   // Set up 7 segment display pins.
  33.   pinMode(dispA, OUTPUT);
  34.   pinMode(dispB, OUTPUT);
  35.   pinMode(dispC, OUTPUT);
  36.   pinMode(dispD, OUTPUT);
  37.   pinMode(dispE, OUTPUT);
  38.   pinMode(dispF, OUTPUT);
  39.   pinMode(dispG, OUTPUT);    
  40.  
  41.   // Set up vibrator pin.
  42.   pinMode(vibratorPin, OUTPUT);  
  43. }
  44.  
  45. void loop() {
  46.   // Read the analog input into a variable, correct for value inversion.
  47.   potValue = 1023 - analogRead(potPin);
  48.  
  49.   // If 10 channels, return a number between 0 and 9...
  50.   // Constrain to catch rounding errors at the top end.
  51.   currentChannel = constrain(potValue / (1023 / channels), 0, channels - 1);
  52.  
  53.   // Show the current channel number on the 7 segment display.
  54.   displayDigit(currentChannel);
  55.  
  56.   // Vibrate if we change channels.
  57.   if (lastChannel != currentChannel) {
  58.     vibStart = millis();
  59.   }
  60.  
  61.   // Keep vibrating for the full duration...
  62.   if ((millis() - vibStart) <= vibDuration) {
  63.     digitalWrite(vibratorPin, HIGH);
  64.   }
  65.   else {
  66.      digitalWrite(vibratorPin, LOW);
  67.   }
  68.  
  69.   lastChannel = currentChannel;
  70. }
  71.  
  72. // Shows a number on the 7 segment display.
  73. // It's a common anode model, so LOW is actually on.
  74. void displayDigit(int digit) {
  75.   switch (digit) {
  76.   case 0:
  77.     digitalWrite(dispA, LOW);
  78.     digitalWrite(dispB, LOW);
  79.     digitalWrite(dispC, LOW);
  80.     digitalWrite(dispD, LOW);
  81.     digitalWrite(dispE, LOW);
  82.     digitalWrite(dispF, LOW);
  83.     digitalWrite(dispG, HIGH);      
  84.     break;
  85.   case 1:
  86.     digitalWrite(dispA, HIGH);
  87.     digitalWrite(dispB, LOW);
  88.     digitalWrite(dispC, LOW);
  89.     digitalWrite(dispD, HIGH);
  90.     digitalWrite(dispE, HIGH);
  91.     digitalWrite(dispF, HIGH);
  92.     digitalWrite(dispG, HIGH);
  93.     break;
  94.   case 2:
  95.     digitalWrite(dispA, LOW);
  96.     digitalWrite(dispB, LOW);
  97.     digitalWrite(dispC, HIGH);
  98.     digitalWrite(dispD, LOW);
  99.     digitalWrite(dispE, LOW);
  100.     digitalWrite(dispF, HIGH);
  101.     digitalWrite(dispG, LOW);
  102.     break;
  103.   case 3:
  104.     digitalWrite(dispA, LOW);
  105.     digitalWrite(dispB, LOW);
  106.     digitalWrite(dispC, LOW);
  107.     digitalWrite(dispD, LOW);
  108.     digitalWrite(dispE, HIGH);
  109.     digitalWrite(dispF, HIGH);
  110.     digitalWrite(dispG, LOW);
  111.     break;
  112.   case 4:
  113.     digitalWrite(dispA, HIGH);
  114.     digitalWrite(dispB, LOW);
  115.     digitalWrite(dispC, LOW);
  116.     digitalWrite(dispD, HIGH);
  117.     digitalWrite(dispE, HIGH);
  118.     digitalWrite(dispF, LOW);
  119.     digitalWrite(dispG, LOW);
  120.     break;
  121.   case 5:
  122.     digitalWrite(dispA, LOW);
  123.     digitalWrite(dispB, HIGH);
  124.     digitalWrite(dispC, LOW);
  125.     digitalWrite(dispD, LOW);
  126.     digitalWrite(dispE, HIGH);
  127.     digitalWrite(dispF, LOW);
  128.     digitalWrite(dispG, LOW);
  129.     break;
  130.   case 6:
  131.     digitalWrite(dispA, LOW);
  132.     digitalWrite(dispB, HIGH);
  133.     digitalWrite(dispC, LOW);
  134.     digitalWrite(dispD, LOW);
  135.     digitalWrite(dispE, LOW);
  136.     digitalWrite(dispF, LOW);
  137.     digitalWrite(dispG, LOW);
  138.     break;      
  139.   case 7:
  140.     digitalWrite(dispA, LOW);
  141.     digitalWrite(dispB, LOW);
  142.     digitalWrite(dispC, LOW);
  143.     digitalWrite(dispD, HIGH);
  144.     digitalWrite(dispE, HIGH);
  145.     digitalWrite(dispF, HIGH);
  146.     digitalWrite(dispG, HIGH);
  147.     break;
  148.   case 8:
  149.     digitalWrite(dispA, LOW);
  150.     digitalWrite(dispB, LOW);
  151.     digitalWrite(dispC, LOW);
  152.     digitalWrite(dispD, LOW);
  153.     digitalWrite(dispE, LOW);
  154.     digitalWrite(dispF, LOW);
  155.     digitalWrite(dispG, LOW);
  156.     break;
  157.   case 9:
  158.     digitalWrite(dispA, LOW);
  159.     digitalWrite(dispB, LOW);
  160.     digitalWrite(dispC, LOW);
  161.     digitalWrite(dispD, LOW);
  162.     digitalWrite(dispE, HIGH);
  163.     digitalWrite(dispF, LOW);
  164.     digitalWrite(dispG, LOW);
  165.     break;
  166.   default:      
  167.     digitalWrite(dispA, HIGH);
  168.     digitalWrite(dispB, HIGH);
  169.     digitalWrite(dispC, HIGH);
  170.     digitalWrite(dispD, HIGH);
  171.     digitalWrite(dispE, HIGH);
  172.     digitalWrite(dispF, HIGH);
  173.     digitalWrite(dispG, HIGH);
  174.   }
  175. }

December 29 2009 at 11 AM

Real-time Sky Hiatus

The output from my real-time sky cam remains inconsistent. The color of the sky was supposed to set the background color of this blog... but I'm having second thoughts.

I was expecting shades of blue, but ended up with yellows and browns... assaults on the eyes that are too much to bear. Until I can muster a better color-sensing solution, I'm returning the blog background to its original light-gray. In the mean time, the sky camera will continue to send its uninspired color values up to Pachube every minute.

And so, failure: The whole idea was to lighten up and relinquish some aesthetic control to an unknowing third party. It was more than I could handle. For shame.

December 28 2009 at 11 PM

Bargaining Chip

December 27 2009 at 2 AM