4x4x4 Cube – Things are getting more serious

Posted on by hukl

After all those blogposts on how to build an LED cube it was time to actually do it. A few weeks ago I build a 4x4x4 cube. Although it is my goal to build a 8x8x8 or even larger cube, I still wanted another prototype to play around with. In case something goes wrong, I would only lose 64 instead of 512 or more LEDs.

Basically I followed the steps from one of my previous posts for this, building a cube from vertical layers. After building the four layers I drilled 16 holes into a 150x150x15mm piece of MDF and adjusted the layers in them using hot glue and this is how it looked like:

Side

Side

The next task was to do the wiring. My favorite for things like this are good old 40 pin IDE cables. Now there are four layers with 16 LEDs on them, meaning that only 20 wires would be needed but these specific wires are quite thin and as I mentioned in earlier posts, bigger cubes need more power. Each layer could use up to 320mA and while that may have even worked with single wires, I just used two wires for each pin. Take a look at the picture with the final case, you can see the pairs of wires.

Versuchswürfel 01

With some more MDF I built the rest of the case. The cube and the top plate are attached to the rest of the case with two screws, allowing me to take it apart again in case a wire falls off or something.

The best part about it: It worked right away!

The 40 pin IDE connector fits onto a / my Breadboard which makes it easy to build a test setup. Everything was until I was trying to multiplex the layers. Since every LED is switched on only for 25% of the time they appear a lot darker. Darker than I expected. Usually people use ultra bright LEDs which are way to bright at 100% but still bright enough when switched on for only 1/8th of the time. My LEDs should have been just fine for a 4x4x4 cube though and so I was getting quite annoyed by this whole issue.

I played around a lot using different circuits, different transistors and MOSFETs. I tried to read about the involved parts and tried to figure out what was wrong. Unfortunately I didn’t get answers right away and didn’t have the right tools at the time. Then I had work to do and the »Versuchswuerfel 01« caught some dust.

Now I’m back with an oscilloscope to figure out what exactly the problem is. I know that there are tons of guides out there about building an LED cube and that there was a new guide on instructables recently which looked quite impressive but I want to understand and control every aspect of it myself. The circuit / board layout, parts, software etc. I want maximum brightness. The ultimate goal is to use an FPGA for this but this seems like a long road ahead considering the basic problems i’m currently dealing with. On the other side I finally get the chance to get acquainted with an oscilloscope. The current setup looks like this, currently dealing with only one LED.

Side

Since I’m using MOSFETs to switch the layers on and off my first guess was that they weren’t opening up wide enough. This turned out to be true and so I tried logic level mosfets which can be directly controlled from the pins of an Arduino but the result was the same. Now with the oscilloscope I could see that the MOSFETs weren’t opening up fast enough resulting in a non rectangular wave and so I tried to use MOSFET drivers. You can see the result on the picture above. A quite clean, almost rectangular wave.

Now while that improved the situation already I could now increase the voltage on the layers to allow more current in the same amount of time. LEDs work with up to 10 times of the regular current but only if they are pulsed. Now since they are on only 25% of the time I want to try to increase the voltage until the LEDs get 80mA so that they appear equally bright to LEDs that are on all the time at 20mA.

To switch the individual LEDs on a layer, I’m using constant current sink LED driver.

Maybe a list of current parts is also helpful:

  • STP16CP05 Constant current LED driver
  • ICL 7667 MOSFET Driver
  • IRL2905 Logic Level MOSFETs

I will experiment some more before I light up the cube again but I will report on my results. If you have any questions leave a comment or write me an email to cubino [at] smyck [dot] org

Your own “DNS server”

Posted on by hukl

DNS is one of the key ingredients of the internet and the world wide web. Without it you would have to type long numbers into the browsers address bar instead of convenient domain names like example.org. Humans seem to remember words better than numbers. In that sense, DNS is like the internets “phonebook”. To look up those numbers, which are the real address of (web)servers in the internet, every computer asks a so called name server to resolve a given domain name to its actual address.

But where do you get a name server address if you don’t have a name server yet? Well, most of the internet service providers just tell your computer to use their name server if you don’t have one already. Recently google announced their name server with a number which is quite easy to remember (8.8.8.8). So where ever you go you shouldn’t have to care about configuring a name server.

On the other side the name server provider can refuse to resolve certain addresses to an extend where it could be called »censorship«. A provided name server can be very slow and degrade your overall internet performance. Fun fact: Most of the times when people cry out “My internet is not working”, faulty or non-reachable name servers are involved.

Luckily DNS is very decentralized. Everyone can have its own name server. There is no magic to it and its very easy to do as well. Most users even have one pre-installed. Its called »bind«. Its quite easy to setup but there are other ones which are more convenient. I use »unbound« locally on my laptop. Where ever I go, I bring my name server with me. If something is not resolving or working, I have a log file to look into it. It allows me to block google tracking domains easily and offers speed and lots of flexibility. The best thing: It’s super easy to set up:

On Mac OS X with Macports run the following in your Terminal:

sudo port install unbound
sudo launchctl load -w /Library/LaunchDaemons/org.macports.unbound.plist

Thats it. Test it in the terminal via:

dig www.slashdot.org @127.0.0.1

Now configure it in the Network Preferences as your DNS server and move on.

Packages for other operating systems should be available.

Why isn’t everybody using a local DNS resolver/cache?

Using public and well known DNS servers has a big advantage. Since all its users are contributing to its cache, 99% of the domains that need to get resolved are already in the cache. This saves time and bandwidth. As karsten pointed out in the comments, it wouldn’t be wise to switch completely to locally installed DNS resolvers. On the other side it has no disadvantages having a DNS resolver installed which is only running / used when you need it. Have a look at the comments for a more elaborate reply.

Instead of using GoogleDNS or OpenDNS only, look for other public DNS servers or set up one on your own for you and everybody else.

Even if you still don’t care to run your own name server, do yourself a favor and inform yourself about DNS. Its something, that doesn’t hurt to know and can be really useful.

Links

Videos now without flash

Posted on by hukl

I bought the Vimeo plus membership for one year and added mobile versions to all videos so that iOS users should be able to watch them without the need for flash. Also if you have the latest YouTube5 Safari extension installed, you should be able to watch the videos with the html5 player.

Back to self-hosted blogging

Posted on by hukl

After quitting this blog and saying goodbye to wordpress for a while I’m back. First I didn’t want to blog at all. Then I started an electronics blog on tumblr. Then I got very annoyed by tumblr. Now tumblr is down for more than 16h hours and I can’t stand it any longer. I was planning to write my own blog software but since this takes too much time than I can afford right now, I’ll use wordpress again. This will be only a temporary solution as wordpress is still very annoying itself (…but still less annoying than tumblr).

I found my old sql dumps but upgrading to the latest wordpress version and fixing all the encoding issues took two hours of my time. Luckily I found this post which solved the problem fast and easy.

Some things still need some adjustments like the theme and the search. Then the tumblr posts need to be migrated and I have to figure out the flattr setup for wordpress. Lets see how long that takes.

3x3x3 Cube with 2nd Board

Posted on by hukl

The code can be found here.