Earlier this month, I completed yet another journey around the biggest star in our galaxy. Some of my beloved family members thought this would be a good occasion to send me some cash, and I also got a gift card for being plain awesome at work. Even though we really do need a bigger car and whatnot, my wife insisted that I only spend this money on myself and whatever I wanted.

Little did she know the can of worms she just opened up.

I took pretty much all of the money and blew it on stuff for my electronics projects. Up to this point, my projects have all been pretty boring simply because nothing ever moved--it was mostly just lights turning on and off or changing colors. Sure, that's fun, but things really start to get interesting when you actually interact with the physical world. With the birthday money, I was finally able to buy a bunch of servos to begin living out my childhood dream of building robots.

My first project since getting all of my new toys was a motorized webcam mount. My parents bought me a Logitech C910 for my birthday because they were tired of trying to see their grandchildren with the crappy webcam that is built into my laptop. It was a perfect opportunity to use SparkFun's tutorial for some facial tracking (thanks to OpenCV) using their Pan/Tilt Servo Bracket.

It took a little while to get everything setup properly, but SparkFun's tutorial explains perfectly how you can get everything setup if you want to repeat this project.

The problem I had with the SparkFun tutorial, though, is that it basically only gives you a standalone program that does the facial tracking and displays your webcam feed. What good is that? I actually wanted to use this rig to chat with people!! That's when I set out to figure out how to do this.

While the Processing sketch ran absolutely perfect on Windows, it didn't want to work on my Arch Linux system due to some missing dependencies that I didn't know how/care to satisfy. As such, I opted to rewrite the sketch using Python so I could do the facial tracking in Linux.

This is still a work in progress, but here's the current facial tracking program which tells the Arduino where the webcam should be pointing, along with the Arduino sketch.

Now that I could track a face and move my webcam in Linux, I still faced the same problem as before: how can I use my face-tracking, webcam-moving program during a chat with my mom? I had no idea how to accomplish this. I figured I would have to either intercept the webcam feed as it was going to Skype or the Google Talk Plugin, or I'd have to somehow consume the webcam feed and proxy it back out as a V4L2 device that the Google Talk Plugin could then use.

Trying to come up with a way of doing that seemed rather impossible (at least in straight Python), but I eventually stumbled upon a couple little gems.

• A GStreamer webcam tutorial
• v4l2loopback

So the GStreamer tutorial walks you step-by-step through different ways of using a gst-launch utility, and I found this information very useful. I learned that you can use tee to split a webcam feed and do two different things with it. I wondered if it would be possible to split one webcam feed and send it to two other V4L2 devices.

Enter v4l2loopback.

I was able to install this module from Arch's AUR, and using it was super easy (you should be root for this):

modprobe v4l2loopback devices=2

This created two new /dev/video* devices on my system, which happened to be /dev/video4 and /dev/video5 (yeah... been playing with a lot of webcams and whatnot). One device, video4, is for consumption by my face-tracking program. The other, video5, is for VLC, Skype, Google+ Hangouts, etc. After creating those devices, I simply ran the following command as a regular user:

gst-launch-0.10 v4l2src device=/dev/video1 ! \
    'video/x-raw-yuv,width=640,height=480,framerate=30/1' ! \
    tee name=t_vid ! queue ! \
    v4l2sink sync=false device=/dev/video4 t_vid. ! \
    queue ! videorate ! 'video/x-raw-yuv,framerate=30/1' ! \
    v4l2sink device=/dev/video5

There's a whole lot of stuff going on in that command that I honestly do not understand. All I know is that it made it so both my face-tracking Python program AND VLC can consume the same video feed via two different V4L2 devices! A co-worker of mine agreed to have a quick Google+ Hangout with me to test this setup under "real" circumstances (thx man). It worked :D Objective reached!

I had really hoped to find a way to handle this stuff inside Python, but I have to admit that this is a pretty slick setup. A lot of things are still hardcoded, but I do plan on making things a little more generic soon enough.

So here's my little rig (why yes, I did mount it on top of an old Kool-Aid powder thingy lid):

And a video of it in action. Please excuse the subject of the webcam video, I'm not sure where that guy came from or why he's playing with my webcam.

Yay! First post in nearly 4 months! I feel kinda bad for leaving my April Fools Day joke on the front page for such a long time, but lucky for me my blog isn't very popular! I could have found myself in a world of hurt.

I'd like to give you all a quick update on what's been going on in my life that somewhat justifies a 4-month window of no blog posts. First of all, we had 25% of our backend development team (1 person, leaving 3 developers) get fired earlier in the year, so the workload at my day job got to be a bit heavier.

Second, my wife and I were pregnant with identical twin girls. It was a relatively high-risk pregnancy, so we spent many days in the hospital for checkups and whatnot. The doctors gave her somewhat strict bed rest orders, and I worked from home since the beginning of July (my job is awesome that way) so I could keep and eye on my wife and help with our soon-to-be two year old son.

Third, we had our identical twin girls this past Tuesday. They arrived at 9:25 and 9:27, and their names are Claire and Jane. Claire weighed 5 lb 3 oz, and Jane weighed 4 lb 14 oz. As expected, they lost a bit of weight at the beginning, but they're starting to gain weight again. My wife and the girls are all doing very well.

My son, on the other hand, is starting to realize that his world is changing quite drastically. We're trying to give him as much attention as we can, but it's definitely not the amount that he's used to. He seems to do very well with his new baby sisters, but there have already been several episodes where he just breaks down. It's sad.

I have a few days of leave and vacation that I'll be taking to help get everything settle at home. The girls are still in the "let's sleep all day and night until we're hungry" sort of phase (which is quite awesome), and my wife is up most of the night with them. That means the only person who doesn't sleep a ton during the day is my son, so we get some good father/son time.

Anyway, on to the nerdy stuff. Since I find myself with a couple hours of downtime here and there, I plan to do a bug-smashing ticket-resolving spree. Just as my blog has sat dormant for months, so have many of my side projects. Now is the time to change that!

I've recently been working on some performance enhancements on my site. Apparently some of my latest articles are a little too popular for my shared hosting plan. The surge of traffic to my site took down several sites on the same server as my own.

My response to the fiasco was to, among other things, implement caching on my site. It seems like the caching has helped a lot. I've noticed that my RSS feeds are hit almost as hard as real articles on my site, and I noticed that they weren't being cached the way I had expected. I tried a couple of things that I thought would work, but nothing seemed to do the trick.

After doing some brief research into the idea of caching my RSS feeds using Django's built-in caching mechanisms, I came up empty. It occurred to me to implement caching in the feed classes themselves. I tried something like this:

from django.contrib.syndication.feeds import Feed
from django.core.cache import cache
from articles.models import Article

class LatestEntries(Feed):
    ...

    def items(self):
        articles = cache.get('latest_articles')

        if articles is None:
            articles = Article.objects.active().order_by('-publish_date')[:10]
            cache.set('latest_articles', articles)

        return articles

    ...

This code doesn't work! When I would try to retrieve one of my RSS feeds with such "caching" in place, I got the following traceback:

Traceback (most recent call last):

  File "/home/wheaties/dev/django/core/servers/basehttp.py", line 280, in run
    self.result = application(self.environ, self.start_response)

  File "/home/wheaties/dev/django/core/servers/basehttp.py", line 674, in __call__
    return self.application(environ, start_response)

  File "/home/wheaties/dev/django/core/handlers/wsgi.py", line 241, in __call__
    response = self.get_response(request)

  File "/home/wheaties/dev/django/core/handlers/base.py", line 143, in get_response
    return self.handle_uncaught_exception(request, resolver, exc_info)

  File "/home/wheaties/dev/django/core/handlers/base.py", line 101, in get_response
    response = callback(request, *callback_args, **callback_kwargs)

  File "/home/wheaties/dev/django/utils/decorators.py", line 36, in __call__
    return self.decorator(self.func)(*args, **kwargs)

  File "/home/wheaties/dev/django/utils/decorators.py", line 86, in _wrapped_view
    response = view_func(request, *args, **kwargs)

  File "/home/wheaties/dev/django/contrib/syndication/views.py", line 215, in feed
    feedgen = f(slug, request).get_feed(param)

  File "/home/wheaties/dev/django/contrib/syndication/feeds.py", line 37, in get_feed
    return super(Feed, self).get_feed(obj, self.request)

  File "/home/wheaties/dev/django/contrib/syndication/views.py", line 134, in get_feed
    for item in self.__get_dynamic_attr('items', obj):

  File "/home/wheaties/dev/django/contrib/syndication/views.py", line 69, in __get_dynamic_attr
    return attr()

  File "/home/wheaties/dev/articles/feeds.py", line 22, in items
    cache.set(key, articles)

  File "/home/wheaties/dev/django/core/cache/backends/filebased.py", line 72, in set
    pickle.dump(value, f, pickle.HIGHEST_PROTOCOL)

PicklingError: Can't pickle <class 'django.utils.functional.__proxy__'>: attribute lookup django.utils.functional.__proxy__ failed

This error took me by surprise. I didn't expect anything like this. I tried a few things to get around it, but then I actually stopped to consider what was happening to cause such an error. My Article objects are definitely serializable, which is why the error didn't make sense.

Then it hit me: the object I was actually attempting to cache was a QuerySet, not a list or tuple of Article objects. Changing the code to wrap the Article.objects.active() call with list().

from django.contrib.syndication.feeds import Feed
from django.core.cache import cache
from articles.models import Article

class LatestEntries(Feed):
    ...

    def items(self):
        articles = cache.get('latest_articles')

        if articles is None:
            articles = list(Article.objects.active().order_by('-publish_date')[:10])
            cache.set('latest_articles', articles)

        return articles

    ...

And that one worked. I would prefer to cache the actual XML version of the RSS feed, but I will settle with a few hundred fewer hits to my database each day by caching the list of articles. If anyone has better suggestions, I'd love to hear about them. Until then, I hope my experience will help others out there who are in danger of taking down other sites on their shared hosting service!

I'm proud to announce the official release of yet another one of my side projects. I call it django-tracking, and it is a simple project capable of telling you how many users are currently on your site. If you look at the bottom of any page on codekoala.com, you will see a demonstration of what this project can be used for.

django-tracking also offers basic blacklisting capabilities. I had a chap who apparently setup a script to spam my blog with rubbish comments every 11 minutes recently. I devised a way to stop the comments from being posted, but I noticed from my logs that the script was still hitting my website consistently over the following days. As a result, I implemented the "Banned IP" feature in django-tracking, and any visitor (or script) accessing my site from that IP address receives an error page. Yay!

If you have "Big Brother"-like tendencies when it comes to your visitors, there is also a way for you to have a "live feed" of active users on your site. Works pretty well, if I do say so myself :)

For more information, hop on over to django-tracking's homepage. There you will also find installation instructions and details for configuration and usage.

Have fun!

I just wanted to update anyone who's interested. As per a request from one CGH, I have created a very simple RSS feed for my blog entries. Now you can always keep up to date with my rants! Don't you feel special.

The feed can be found at http://site.vcboard.net/feeds/latest/