Raspberry Pi: Tao Te Ching Morse Code LED 
Sunday, March 24, 2013, 18:27
Posted by Administrator
I spent my three day spring break this year working with the Raspberry Pi GPIO and learning some more about python in the process. My first task was to get all the necessary GPIO packages installed on one of my dedicated raspbmc machines. The RPi.GPIO Python library was pretty easily installed with pip and was much friendlier to work with than I was expecting.

I used an old IDE hard drive cable to interface with the Pi's GPIO pins. This proved to be one of the harder parts of this project since these type of cables don't have the same number of pins as the Pi's GPIO. For lights I used a doubled up white LED + Resistor combination I had lying around.

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To start with I just got an initial feel for the outputs by plugging the LEDs into the 3v power and ground. I then used the RPi.GPIO python library to get the lights blinking on and off at a medium pace. The rest of the night was spent trying to think of something more interesting a single light could do.

After some light googling I eventually became inspired by m0xpd's gmail notifier script. I loved how elegant the design was and decided to apply the same concept to read in a text file and display it all in morse code via the LEDs.

Python is such a joy to work with, in about half an hour I was able to finish forking over m0xpd's code into what I wanted. Coolest thing I learned in the process was about anonymous functions by using the keyword lambda. I also found that there aren't any morse code standards for some common ascii characters like asterisks or dashes so I came up with a few substitutions I thought were appropriate.

One of my favourite books is the Tao Te Ching (especially the translation by S. Mitchell), so I decided to use that to power this LED art piece. Here is a video of the project running. The rest of the day was spent monitoring how long it took the contraption to process the entire book. It finished a little while before bed, taking 637 minutes and 4.257 seconds to run through the entirety of the text.

The full code I used for this project is available in an easy to read color scheme at pastie.org here.

Next up on my list of personal things to work on is to extend my old binary bash clock concept to work with the Pi's GPIO. It turns out that there are exactly as many controllable outputs ( Seventeen ) as I need to run the kind of display I want without using a decoder or shift register to address all the LEDs. I've even ordered some ping pong balls to use as LED diffusers. :)

For now though, I'm calling this weekends endeavour finished.

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Simple Kindle Temperature Display 
Thursday, February 7, 2013, 15:41
Posted by Administrator
I've been wanting to make an e-paper temperature display ever since seeing the beautiful weather forecast display that Matthew Petroff put together but as is my style I wanted to do something much simpler and easier to get running. My main self imposed requirement was to make something that would work on an unrooted device. With my kindle touch laying around mostly unused the last few weeks I finally got determined to put it to some better use around the apartment.

I started off with my old weather grabbing script to pull the current temperature information from Wunderground. Wunderground claims to be phasing out their API that I like, but it shouldn't be difficult to scrape another site once they finally can it. I cut out a lot of the extra information I had been grabbing before since I wanted to dedicate this display to just temperature information.

The revised bash script follows below:

# Temperature Grabbing Bash Script From Wunderground
# Created by Spike Snell 2013

# Make sure there is an argument which could have a zip
if [ $# -lt 1 ] ; then
echo "Please include a zipcode as an argument such as: ./weather.sh 72703"
exit 1

# Grab the Zipcode from the command line argument


# Grab the content from the Wunderground API
weather_wget=`wget -q $url -O -`
weather_xml=`echo "$weather_wget" | sed 's/<current_observation>.*//'`
weather=`echo "$weather_xml" | sed 's/></>\n</g'`

# Get the temperature in C
temp=`echo "$weather" | grep -e '<temp_c>' | \
sed -e 's/\t\t<temp_c>//' -e 's/<\/temp_c>//'`

# Print out all the information
echo $temp

# Write it to a gif
echo $temp | convert -pointsize 555 text:- n.gif

The biggest change in the code from the old one is that I'm now using imagemagick to do a convert on the temperature text into a gif file. This is because I found that the kindle's experimental web browser was very iffy about displaying very large fonts, it would work about 1/10th of the time. It was able to display a large picture great though.

This whole project was made much simpler than Matthew's by driving the process with the kindle's built in web browser. I have a server running a lamp stack that I like to use and put the previous shell script and the following php code up on.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<meta http-equiv="refresh" content="360" charset=UTF-8">
<META NAME="DESCRIPTION" CONTENT="A small temperature indicator to run as an art piece displaying degrees C.">
<META NAME="KEYWORDS" CONTENT="temperature,art,large,tool">
<title>Current Local Temperature Indicator</title>
<body bgcolor="#FFFFFF">
$z = 72703;
if (isset($_GET['z'])) {
$z = $_GET['z'];
$t = `./t.sh $z`;
# convert to F
$f = $t*9/5+32;
echo $f;
<img src="n.gif">

All that was left to do was to point the kindle's browser towards the php file, this triggers the bash script, writes the image and does a simple conversion of C -> F degrees to display above the large C readout. Voila! A temperature readout, self updating every 6 minutes with a meta refresh. So now everything is finished, except the kindle has one last gotcha, it blanks the screen and displays a screensaver after about a 15 minute inactivity period. Luckily this can be easily disabled. At the home screen of the kindle you can enter "~ds". This will disable the screensaver until the device is restarted.

Now some glamour shots of the kindle temperature display in operation, along with a closeup of my tacky wall-mounting job.

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Ascii Snow and Rain 
Wednesday, December 26, 2012, 15:39
Posted by Administrator
My favorite twitter feed at the moment is climagic. He posts an assortment of great little scripts and other cli tips and tweaks at least a few times a week. One of the neatest things things he posted in a long while is his bash ascii snow simulator.

The code for it is below:

c=$(tput cols);clear;while :;do echo $(tput lines) $c $(($RANDOM%$c));sleep 0.1;done|gawk '{a[$3]=0;for(x in a){o=a[x];a[x]=a[x]+1;printf"\033[%s;%sH ",o,x;printf"\033[%s;%sH*\033[0;0H",a[x],x;}}'

I've modified it a very little bit and made a rainy windsheild simulator as well:

c=$(tput cols);clear;while :;do echo $(tput lines) $c $(($RANDOM%$c));sleep 0.1;done|gawk '{a[$3]=0;for(x in a){o=a[x];a[x]=a[x+1]+1;printf"\033[%s;%sH ",o,x;printf"\033[%s;%sH.\033[0;0H",a[x],x;}}'

The most interesting part of these to me is how few characters it takes to generate something so visually interesting. These scripts can be shortened a bit if you are running them from the command line by removing the c variable for columns, but when running from a script this variable isn't passed so I've left it in.

Particularly fun has been running the snow simulator on an old-style television with a Raspberry Pi with the font size way way up.
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