Recent blog entries for jkkroll

Digital Gaming Table Quick Prototype

I’ve been fascinated by the digital gaming tables I’ve seen on the net for a while now. This weekend I got the bug and decided to see what I could do with just the stuff I had lying around the house. I already had a small Ikea table and ceiling mounted projector up in the loft, so I figured I would try a top-down projection by placing a mirror in the beam path. A quick search out in the garage turned up a donor full-length mirror*. I cut it down to a decent size and proceeded to stand on a chair, holding the mirror in place to get an idea of how it would look.

It wasn’t too bad. Obviously I would eventually need to switch to a front surface mirror because I got quite a bit of ghosting, but the image was usable. Now I just needed a way to hold the mirror in place. Another rummage through the garage and I came back with an Ikea clamp-style goose neck lamp with a teeny burned-out halogen bulb. I knew it was unlikely I’d ever get around to replacing the bulb, so the lamp was harvested also**. Here’s the result:

I have checked several times to make sure the mirror isn’t getting hot, because I don’t want the glue to give way and drop the mirror crashing down on the table. No problems so far, it’s not even getting warm. Not bad for an hour’s worth of prototyping! And when I’m done, I can just un-clip the mirror, re-focus the projector and watch movies again.

*Every time I find something useful out in the garage, it reinforces my pack-rat tendencies. By this point in my life, I think it’s hopeless.

** See? There’s another one. Good thing I saved those, instead of getting rid of them!

Syndicated 2012-03-25 22:04:34 from

Beagle-Book Update

Doesn’t look a whole lot different, but I’ve added a small cooling fan for the DLP and it’s been rewired to run from a single 5V@2.6A wall wart (sorry for the shoddy cell-phone pic) :
Case 4

Syndicated 2011-06-24 19:37:58 from

Beagle Box

I got a BeagleBoard for Father’s Day. My plan is to put the BeagleBoard, the Pico Projector and a battery in a small box, write some ALife software and carry around a virtual world. Tonight I started mounting the board and projector inside a fake book:
Case 1
Case 1
Case 1

Syndicated 2011-06-24 04:55:12 from

Simple Embedded Architecture for Robot Learning and Emotion

I’ve been working on a paper about robot learning for over a year now, more as a place to organize my thoughts than anything else. This paper outlines some ideas I’ve been having about how to implement a learning system that let’s a robot relate state-action sequences to a result. It’s still extremely sketchy, but I thought I’d make it public:
Simple Embedded Architecture for Robot Learning and Emotion
Sorry for the shoddy formatting, but that results from publishing a Google Doc as HTML.

I also have a few background documents that may be interesting* to some:

Senses/States Matrix
Emotional Effects on Outputs
Robot Emotions versus Movements

My current mental obsession is an ALife simulation running under Linux, and I thought I would try out this learning architecture in a simulated environment on a capable processor.

*I find this stuff extremely interesting, but then according to my teenage daughters I’m weird. Of course they think weird is a compliment.

Syndicated 2011-05-25 18:55:36 from

Something useless for xmas

I needed a ~$5 gift for family xmas this year, and was at a loss. Then I remembered the Useless Machine from Make, also known as a “Leave Me Alone Box.”  I had a $5 box from the thrift store, a smaller version of the one I used for my iPad Charger.  After a lot of planning in AutoCAD and even more trial and error I came up with this:

It took me a while to figure out how to put it together with the cam attached to the lid, and my daughter suggested a rod & tube setup:

The cam is connected to the lid through a bearing and a brass “bicycle fork”:

When the cam spins, it lifts the lid enough for the arm to come out and flip the switch.

One thing that I did slightly different was use a 5V DPDT relay to reverse the motor instead of a DPDT  switch. This allowed me to use a SPDT switch with a lower actuation force.

Syndicated 2010-12-19 05:08:22 from

Perl for Puzzlers

I was working on creating a puzzle a couple of weeks ago and needed sets of a dozen 5-letter words that all “interacted” in a certain way (sorry, don’t want to give away too much).  One of the software guys here at work suggested a Perl script to find sets words, specifically Strawberry Perl. I have been programming since I was a kid (basic on a VIC-20) but lately have been resistant to learning new languages because I can usually accomplish my goals with the languages I already know. This time I decided to take his advice and was pleasantly surprised with the simple learning curve and thought I’d pass on a bit of intro on how to set up and start using Perl to help create puzzles.


I am not a Computer Scientist, nor do I play one on TV. This is a description of how I went about solving a specific problem, not necessarily the best method. For informational purposes only. Use at your own risk.

Installation of Strawberry Perl was completely straightforward on my XP machine. I haven’t tried any Win7 installs, but the home page suggests it is just as simple. I just downloaded the Windows installer and let it run. This will install Perl on your machine let you run scripts from the command line.

1. Create a folder to place all of my code and research material.

2.  Create a text file in the folder where I had all of my puzzle related info called “prompt.bat” (no quotes), and consisted of the single word “cmd” (again no quotes). Double-clicking this file will open a command prompt within the folder so you can launch the scripts easily.

3. Download a word list that can be easily read into your script. I used output from Tea, but I also found some other word lists here:

4. Create a text file (I prefer Notepad++ for text editing. Be sure to set the Language to Perl to get the correct syntax hi lighting) with the name of the puzzle and a “.pl” suffix. This file will be your Perl Script.

5. Start the script with “#!/usr/bin/perl” This tells the computer that it is a Perl script.

6. Here’s a script I wrote to find all the rotations of a word (anyone who saw my sample puzzle on the forum may recognize this) (Save target as… or you may get an error. No idea why). You can run this by typing “perl words.txt” at the command prompt.

#use strict;
my %words;
my $i;
open(DATAIN,”<$ARGV[0]“) || die “cannot open \”$ARGV[0]\”: $!”;
while(my $line = <DATAIN>){
$line =~ s/\s+//;
$words{$line} = 1;
foreach my $word1 (sort keys %words){
my $num=0;
my $word=$word1;
print “-$word\n”;
for($i = 1; $i < length($word1); $i++){
$word= rotate($word);
print “$word\n”;
sub rotate{
my $foo=shift;
my $out=substr($foo,1,length($foo)-1).substr($foo,0,1);
return $out;

The beginning of the script reads in the command line argument (words.txt in the example above) then reads the word list into memory. Specifically into a hash structure named words hash, but I’ll discuss that later. While reading the file into memory, it also strips carriage returns and unprintable characters.

Next the script steps through each entry in the hash (%words). It takes this entry, and rotates it using the rotate function, once for each letter in the word. This way we end up with all possible rotations.

In a future post I’ll cover some of the neat things you can do once you have a word list in memory.

Syndicated 2010-08-24 18:57:35 from

Portable Electrick Storage Device – Mark I

My daughter has swim meets every Saturday morning from 7am until around 1pm. During this time she is actually swimming a total of about 4 minutes, so the entire family tries to stay occupied the rest of the day. Almost every week someone complains “Oh, man! My iPod is dead!” Answering the tinkerer’s call to arms, I would like to present the Portable Electrick Storage Device Mark I:



USB Connectors

Charging my iPad


  • Box – $6 brand new at the local thrift store, I only added electronics and handles. (I need to head back and get a couple more!)
  • Battery – 12V 7Ah (~12 iPod charges or 3.5 iPad charges)
  • Output – 5V @ 1.5A (will charge iPad while watching video)
  • Connectors – 3x USB Type-A female
  • 3A fuse directly on battery
  • Power switch with blue LED indicator

Plans for the future:

  • “Working” steam power plant
  • Microcontroller based monitor (Battery charge level, internal temp, etc) with 128×128 OLED screen
  • Embedded wireless web server (WRT54G based)

Syndicated 2010-06-21 19:29:33 from

Steampunk PDA – Again

I have been convinced to add the Steampunk PDA back to my list of projects I am allowing myself to work on, so the list currently stands as Deskpet, Mazetrix, PDA and notebooks. I ordered the accelerometers for the next 3 Mazetrix tiles (should be here Monday), and I should be building a couple of notebooks for some guys at work, but this sounded like more fun.

I have been thinking about the PDA for a week or two now, and decided to make a custom case rather than attempting to use a pocketwatch case. I picked up a 2″ brass pipe fitting from the hardware store and  started shaping it on the lathe. It should be just about the right size…

PDA Case

Steampunk PDA Case - Size Comparison

PDA Case

Steampunk PDA Case

Steampunk PDA Case

Steampunk PDA Case

Steampunk PDA Case

Steampunk PDA Case

Syndicated 2009-07-12 02:47:50 from

#mazetrix video 1

I spent about 4 hours programming last night trying to simulate the physics of a rolling ball on the AVR. I think it turned out pretty well:

Here’s the timer interrupt that services the analog to digital converter and the multiplexing of the LEDs:

static unsigned char activeLine=0;
static unsigned char adcChannel=0;
case 0: x_accel=(ADCH-x_flat)/10;
if((x_loc<500)&&(x_accel<0)){ x_accel=0; } if((x_loc>7500)&&(x_accel>0)){
case 1: y_accel=(y_flat-ADCH)/10;
if((y_loc<500)&&(y_accel<0)){ y_accel=0; } if((y_loc>7500)&&(y_accel>0)){
// y_vel=0;
case 2: z_accel=(ADCH-125);
default: adcChannel=0;


And the main loop:


if(x_loc<0){ x_loc=-x_loc; x_vel=-x_vel; } if(x_loc>7999){
if(y_loc<0){ y_loc=-y_loc; y_vel=-y_vel; } if(y_loc>7999){
x_pos=(unsigned char)(x_loc/1000);
y_pos=(unsigned char)(y_loc/1000);


Syndicated 2009-06-26 04:03:08 from

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