Category Archives: Linux

Cloning Simulink…in Python

For a while now I have been working on a bench supply. As part of this I have been trying to get a PID controller to work. At first it was simple, but after asking my Dad about it (he does power electronics), he suggested that I use a cascaded PID loop for controlling the voltage and current using the voltage alone. I have sort of a bench model going, but I don’t really want to start construction until I have everything finalized since blowing things up and making mistakes is kind of expensive for my meager college student budget. Tweaking that without a working bench model that I am willing to blow up is kind of hard, so I started trying to figure out how to simulate it. Being partial to simulink (I’ve used it before with some nice pre-built blocks), I wanted to be able to lay it out graphically like control system diagrams usually show and I also wanted to be able to view plots over time. So thus was born my latest project: SimuPy.

Python seemed like an ideal language for this since I wanted it to look nice, be extensible, and be almost universally cross platform. I am relying heavily on the Qt library because it runs on almost anything and it has the ability to use slots and signals on pretty much any object as well. I guess another option would have been Java, but seeing as I don’t like Java that much, Python was what I went with. In addition, I am weighing a couple other options:

  • At the sacrifice of portability, I could make the interface half in C++ and half Python so that I still keep the extensibility without having the requirement of installing python on the person’s computer to get it to work. The simulation part would then turn into a python library that the program would load.
  • Write the entire thing in C++ for speed and true multithreading and use Python solely for extensions. This would be a little more difficult since I kind of leverage the dynamic typing thing that Python has going on.

So far, my current structure has everything based on a Model which contains Blocks. In addition, there is a simulation Context which holds information about each Block and where the simulation is in terms of the current step (simulations are stepped over time (dt)). Contexts are also where a Block will store all of its information that it needs to retain during the current step and in the next step. A Block is an operation over time in the flow of the simulation: it could be a simple addition, maybe a derivative or integral, or it could be a full PID controller. Blocks declare themselves to have a number of Input objects and Output objects. Inputs/Outputs are named and have a slot/function called set which sets the value of the input or output. Outputs have a signal called ‘ready’ which inputs connect their ‘set’ slot to. When an output’s ‘set’ method is called, it emits its signal. When an input is set and it sees that all inputs attached to its block are set, it performs a “step” on the block. In addition, there are 3 special blocks: An EntryBlock, ExitBlock, and ModelBlock. Entry and Exit blocks are used in models since a model can have “Entry” and “Exit” points. These points can be used to loop a value from an Exit to an Entry (if they have the same name) or can be used as Input and Output objects if the Model is placed inside a ModelBlock. ModelBlocks are blocks which contain a model which they execute in a child simulation Context to their context. In this way, blocks can be nested. If one creates a Model with 2 Entries and 2 Exits with a pair of those Entries and Exits having the same name and then the Model is attached to a ModelBlock, the ModelBlock will have 1 input and one output to corrispond to the free Entry and Exit on the Model. Models can’t be recursive, but they can be nested so as long as a higher level block doesn’t contain a block which at some child level contains the same higher level block, there can be some sense of re-usability and modularity to a simulation.

Blocks are subclassed into a package called model. The file in the model package defines the basic form for a block and then the individual modules in the package define more specific blocks. The blocks then have their constructors cached by reflection so that a block can be constructed by simply naming its name. To extend the blocks available in a simulation, all that must be done is to drop the new module python file into the model folder. I am considering changing this a bit to separate out user-added modules from the “system” modules in kind of the same fashion as I did with the WebSocketServer where I had the files in a folder be loaded into the context of another package.

Simulations are to be stored in an XML format which is going to be more or less human readable and should preserve the look and feel of the simulation. I am still working on the exact format at the moment, but that is the next step.

As for the GUI, I plan on using Qt since it seems the most cross-platform (sorry GTK…Windows needs too much help to load you and PyDev in eclipse doesn’t like the whole introspection thing). I plan on releasing the project under the Apache License (but don’t yet quote me on that or hold me to it…I may choose a different license later once I get more of a feel for how the project would be used). Either way, I plan on publishing the source code on github since it looks like nothing like this really exists in a simple form. Sure, there are clones of Simulink to work with Octave and things like that, but it doesn’t look like there are few, if any, stand-alone applications that do this (except perhaps a paid program called, but this should be able to duplicate the functionality of that program as well). I guess it is kind of a niche market since the only people who do this kind of thing usually can afford Simulink and Matlab.

For the record, I do have access to Simulink and Matlab through the University I am attending, but where would the fun be in that?

The first week or two with Arch Linux

After some frustrating times involving Ubuntu 12.04, hibernation, suspending, and random freezing I decided I needed to try something different. Being a Sandy Bridge desktop, my computer naturally seems to have a slight problem with Linux support in general. Don’t get me wrong, I really like my computer and my processor…however, the hardware drivers at times frustrate me. So, at my wits end I decided to do something crazy and take the plunge to a bleeding edge rolling release linux: Arch Linux.

Arch Linux is interesting for me since its the first time I have not been using an operating system with the “version” paradigm. Since its a rolling release it is prone to more problems, but it also gives the advantage of always being up to date. Since my computer’s hardware is relatively new (it has been superseded by Ivy Bridge, but even so its driver support still seems to be being built), I felt that I had more to gain from doing a rolling release where new updates and such would come out (think kernel 3.0 to 3-2…Sandy Bridge processors suddenly got much better power management) almost immediately. So, without further adieu, here are my plusses and minuses (note that this will end up comparing Ubuntu to Arch alot since that’s all I know at the moment):


  • It was actually very easy to install. Since I have had problems with net installs, I did a core install and then updated it. I practiced several times beforehand on virtual machines, including using existing partitions and such. Although the initial downloads took some time (the lack of curl in the core install was kind of upsetting since I couldn’t use rankmirrors to get better speeds), after that it was pretty fast. Thanks to considerable documentation and a few practice runs, getting an X enviroment set up using Gnome 3 (and gdm…I like the graphical logins) didn’t take long at all. It took a bit of coaxing (read: google + arch wiki) to get things such as networkmanager running and such, but with time I had it all figured out and I managed to get the whole system running more or less stably within a day.
  • It boots faster than Ubuntu and is more explicit about what exactly it’s doing. I liked the Ubuntu moving logo thing, but I do actually enjoy seeing what the computer is doing when it boots. Coming from pure asthetic reasons, it gives the computer more of a “raw” feel which for some strange masochistic reason, I enjoy. The slowest part is initializing the networks and if that didn’t have to happen the entire system could boot in under 60 seconds after the bios gets done showing off its screen.
  • The documentation is awesome. Clearly, people have spent lots and lots and lots of time writing the documentation in the wiki for Arch. It certainly made setting up easier since many of the random corner cases were in the troubleshooting section of severl articles and I ended up running into a couple of them. One thing that was easier to set up than in Ubuntu was suspending and hibernating (at least getting it to work reliably). With some help from the forum (see next point) and a few pages of documentationon pm-utils I got suspend, resume, and hibernate (!!!) running. I haven’t even gotten hibernate to work in Windows.
  • The community is great. I rarely have been able to get a question answered on the Ubuntu forums since they are so conjested. I asked a question on the arch bbs and in less than a day I had a response and was able to do some trial + error and troubleshooting involving the suspend and hibernate functionality of my computer.


  • The rolling release model breaks things occasionally. Recently, the linux-firmware package was updated and this caused my wireless card to stop working since it could no longer find the drivers. I wasn’t sure why, but I have just downgraded the package and blacklisted it for upgrades. Hopefully that doesn’t kill me later (it probably will), but if it does by then I hope to have figured out what is wrong.
  • With great power comes great responsibility. The sheer flexibility is great since I don’t have a bunch of extra packages I don’t need, but at the same time when I was practicing with the VMs, I was able to get myself stuck in a hole where the only solution was to re-format the drive. However, ever since a mishap with Ubuntu (the themeing engine changed all my stuff to black on black or white on white for the text) I have separated out my home folder from the system so that I can easily re-format and re-install the system without losing all my stuff (all 132Gb of it).
  • This isn’t a problem for most people, but it doesn’t access the hard drive as often as other distros. Why is that a con for me? Well, I have a western digital green hard drive which has an automated parking feature which parks the heads after 10 seconds of inactivity. Well, in windows this doesn’t matter, but in linux since it touches the filesystem every 11-15 seconds or so, that results on a LOT of head parkings. Considering that the heads are only rated for 300K cycles and people have reported reaching that in less than a year, it is a real issue. I have a program (wdantiparkd) which writes the hard drive every 7 seconds while watching to see if anything else has written to the hard drive so that it hangs up after 10 minutes rather than 10 seconds. It helps, but it worked better on Ubuntu.

Overall, this experience with Arch has allowed me to become much more familiar with Linux and its guts and slowely but surely I am getting better at fixing issues. If you are considering a switch from your present operating system and already have experience with Linux (especially the command line since that’s what you are stuck with starting out before you install xfce, Gnome, KDE, etc), I would recommend this distribution. Of course, if you get easily frustrated with problems and don’t enjoy solving them, perhaps a little more stability would be something to look for instead.

Here is my desktop as it stands:

Arch Linux with Gnome 3

Arch Linux with Gnome 3

Case LEDs Software

So, I have just cleaned up, documented a little better, and zipped up the firmware and host side driver for the case LEDs. The file does not contain the hardware schematic because it has some parts in it that I created myself and I don’t feel like moving all the symbols around from my gEDA directory and getting all the paths to work correctly.

The host side driver only works on linux at the moment due to the usage of /proc/stat to get CPU usage, but eventually I plan on upgrading it to use SIGAR or something like that to support more platforms once I get a good environment for developing on Windows going. If you can’t wait for me to do it, you could always do it yourself as well.

Anyway, the file is here: LED CPU Monitor Software

Here is the original post detailing the hardware along with a video tour/tutorial/demonstration: The Case LEDs 2.0 Completed

The Case LED v. 2.0: Completed

After much pain and work…(ok, I had a great time; let’s be honest now)…I have finished the case LEDs!

Pursuant to the V-USB licence, I am releasing my hardware schematics and the software (which can be found here). However, it isn’t because of the licence that I feel like releasing them…it is because it was quite fun to build and I would recommend it to anyone with a lot of time on their hands. So, to start off let us list the parts:

  • 1 ATMega48A (Digi-key: ATMEGA48A-PU-ND)
  • 1 28 pin socket (Digi-key: 3M5480-ND)
  • 2 3.6V Zener diodes (Digi-key: 568-5907-1-ND)
  • 2 47Ω resistors (Digi-key: 47QBK-ND)
  • 1 39Ω resistor (Digi-key: 39QTR-ND)
  • 1 15Ω resistor (Digi-key: 15H-ND)
  • 3 100V 300mA TO-92 P-Channel MOSFETs (Digi-key: ZVP2110A-ND)
  • 3 2N7000 TO-92 N-Channel MOSFETs (Digi-key: 2N7000TACT-ND)
  • 1 10 Position 2×5, 0.1″ pitch connector housing (Digi-key: WM2522-ND)
  • 10 Female terminals for said housing (Digi-key: WM2510CT-ND)
  • 1 4-pin male header, 0.1″ pitch for the diskette connector from your power supply (You can find these on digikey pretty easily as well..there are a lot)
  • 2 RGB LEDs (Digi-key: CLVBA-FKA-CAEDH8BBB7A363CT-ND, but you can you whatever you may find)
  • 4 White LEDs like in my last case mod
  • 1 Prototyping board, 24×17 holes

The schematic is as follows:

Schematic (click to open full size)

The parts designations are as follows:

  • R1: 15Ω
  • R2: 39Ω for the Red channel
  • R3: 47Ω for the Green channel
  • R4: 47Ω for the Blue channel
  • LED1-4: White LEDs of your choosing. Make sure to re-calculate the correct value for R1, taking into account that there are 4 LEDs
  • LED5-6: The RGB LEDs. The resistor values here are based on the part I listed above, so if you decide to change it, re-calculate these values.
  • Q1-Q3: The P-Channel MOSFETs
  • Q4-Q6: The N-Channel MOSFETs
  • Z1-Z2: The zener diodes
  • U1: 16Mhz Crystal
  • C1-2: Capacitors to match the crystal. In my circuit, I think they were 33pF or something
  • CONN-PWR: The 4-pin connector for the diskette
  • CONN-USB: The USB connector. You will have to figure out the wiring for this for your own computer. I used this site for mine. Don’t forget to twist the DATA+ and DATA- wires if you aren’t using a real USB cable (like me).
  • C3: Very important decoupling capacitor. Place this close to the microcontroller.

As I was building this I did run into a few issues which are easy to solve, but took me some time:

  • If the USB doesn’t connect, check the connections, check to make sure the pullups are in the right spot, and check to make sure the DECOUPLING CAPACITOR is there. I got stuck on the decoupling capacitor part, added it, and voila! It connected.
  • If the LEDs don’t light up, check the connections, then make sure you have it connected to the right power rails. My schematic is a low-side switch since the LEDs I got were common anode. I connected both ends to negative when I first assembled the board and it caused me quite a headache before I realized what I had done
  • Double and triple check all the wiring when soldering. It is pain to re-route connections (trust me…I know). Measure twice, cut once.
Although I already have a link above, the software can be found here: Case LEDs Software

So, here are pictures of the finished product:

LEDs shining magenta

LEDs shining orange

LEDs shining green

With its guts hanging out

The mounting viewed from the outside

Mounted onto the front fan grille

Case LEDs version 2.0

So, as usual after I completed my LED case mod I asked myself, how can I could make it even cooler? Thus was born the idea for Case LEDs v. 2.0.

The Idea: Wire up some LEDs so they are controlled by the computer to vary their intensity or something based on the CPU usage.

The Implementation: Using RGB LEDs, some small MOSFETs, and a microcontroller make a USB controlled light generator that takes as input a number representing CPU usage.

In the 3 weeks since I put the white LEDs in my case I have been working on this thing in my spare time (mostly weekends…homework has just been swamping me during the week) and this past weekend I finally got it to connect through the USB using the V-USB library and so I have made a lot of progress. At the moment it is perfectly capable of displaying CPU usage by way of color (it is really cool to watch), but I still want to add a few features before I release the source code (and I also need to test it to make sure it doesn’t crash after 2 days or have some horrible memory leak in the host software or something…).

Since I am running linux, the host software was developed linux specific, but later I will add support for Windows since I plan on installing Windows on my computer for gaming at some point. There are two parts to the software: The device firmware and the host software. To minimize USB traffic, the firmware does the conversions from cpu usage to RGB and also the visual efffects. All the host software has to do is read the cpu usage and tell the device about it.

The hardware isn’t incredibly complex: It uses an ATMega168A microcontroller (I am going to be aiming for a smaller 14-18 pin microcontroller eventually…this one is just too big and it would be a waste) to control some MOSFETs that turn on and off the LEDs. The LEDs I got were some $0.55 4-PLCC ones from Digikey which I have soldered some wires to and secured with hot glue (my first try looks awful with the hot glue everywhere…the 2nd one looks amazing since I figured out that hot glue melts before heat shrink shrinks so I could put the glue inside the heat shrink). There are 2 MOSFETs per LED channel in a complementary logic configuration. Since the LEDs are common anode, the MOSFETs control the cathode wire and so there isn’t an inverting effect (put in a 1, get out a 0 and vice versa) like what usually happens with complementary logic. The whole system runs at 3.3V since I didn’t have any 3.6V zener diodes to use for the USB pins to keep the voltage levels in check so that it would be able to talk to the computer. Apparently the voltage levels are very strict for USB and my first few tries of getting this to work didn’t communicate with the computer because of the voltage levels coming out of the USB pins. After I changed the voltage to 3.3V it worked perfectly on the first try. Eventually this is going to connect to one of the internal USB connectors on the motherboard with power supplied by the same 4 pin connector I used for my white LEDs. I am debating running it entirely off USB power, but I am still not sure since that would limit any future expansion to 500mA of current draw and with the planned configuration it will be drawing between 250-300mA already.

Anyway…I plan on making a tutorial video of sorts along with pictures and schematics since in reality aside from the programming this was an easy project. I just need a week or two to get all the parts soldered together and the program finalized and then I’ll know exactly how much this thing costs to build.

Modifying my computer case

The computer

In November I purchased the parts for a new computer since mine was getting very old (I got it in 2006 and even then it wasn’t exactly top of the line). I put it together and it has been performing admirably for a couple months now. I was researching graphics cards and it occurred to me that I would have to move my hard drive up a slot to fit a large graphics card in my case.

After moving stuff around inside

So, I opened the case and started moving stuff around. I also decided to re-organize the cables so that they wouldn’t be dangling precariously above the CPU fan by stuffing them behind the HDD cage. During that process I took some strain off the SATA cables (they are kind of stiff and I think they were putting undue stress on the sockets on the motherboard, so I moved them around so that they wouldn’t be so convoluted). After finishing all this it occurred to me that my case would look sweet if I were to add some LEDs to it. I then set out to install some LEDs.

The grille and power connector

In the front of the case there is a plastic piece that covers the metal body of the case and also holds the power button, reset button, and HDD light. This case has a grille on it to allow air to pass through into the front fan (if I had one installed).

I decided that this grille could look awesome if it had some backlighting. I had considered using a lighted fan for this purpose before, but since fans are mounted on the inside of the case it would project the shadows from the internal metal structure onto the plastic grille, ruining the effect. I decided to mount some white LEDs on the inside of the plastic piece pointing towards the inside of the case so they could shine on and illuminate the part behind the grille to give a “glowing” effect. Here is what I used:

  • Some spare really thick black matte cardstock my sister let me have (she is into artsy things)
  • 4 White LEDs that I had lying around
  • A 15Ω resistor to limit the current (4 LEDs @ 25mA each comes to 100mA at a voltage drop of 3.5V)
  • A .1″ header I had in a parts box
  • Some wire
  • Some tape

The spider wires

I started out by soldering the header to some wires to take the 5V and GND line off of the small .1″ power connector in my computer. I then put the resistor on the positive rail and then split everything off into 4 wires (8 in total: 4 power, 4 ground). The result looked rather like a spider in my opinion. After that it was a relatively simple job of soldering the long lead of the LEDs to the positive rail and the other side to the negative rail. Thus, the LED assembly was completed.

Matte board and aimed LEDs

The more difficult part was attaching the matte board to the metal part of the case and then aiming the LEDs. The matte board was necessary because without it the LEDs reflected a little too well off the metal of the case and they could be clearly seen through the grille. I cut the matte board into two pieces large enough to cover the metal on either side of the grille and used tape to hold it in place. One hitch came up with the wires going to the front of the case: the hole for the wires was right beneath one of the grilles and was not easily covered by the cardstock. I ended up just basically laying the cardstock over the hole and wires and moving them around so as to not be visible through the grille. The next bit of matte board I used was to create a shroud of sorts around the HDD and power lights since the LEDs were bright enough that they shined through the bezels for those lights as well. I then spent a while aiming the lights until I was satisfied and then I put the computer back together so I could enjoy my new lights.

The Final Effect

All in all my specs are as follows:


Ubuntu 9.04

I have just installed Ubuntu 9.04 Netbook Remix on my Acer Aspire One and I have to say it is pretty awesome. First of all, it really does boot in 30 seconds. It took 28 seconds to get to the login screen which is most of the booting. From there it was just the normal login stuff, so it was very fast. Secondly, the Suspend/Resume is also very fast. Fast fast fast. That seems to be the point of this distro. Anyway, I’m definitely keeping this one on my computer.

Ubuntu 9.04 Netbook Remix

Ubuntu 9.04 Netbook Remix

Ubuntu Netbook Remix & MS Office

I just got my Aspire One back from Acer Repair (finally) and they managed to fix it this time (third time). I promptly installed ubuntu 8.10 on it to try out Netbook Remix and so far I have to say that I really like it. My screen seems spacious (except for a few programs) and it is easy to see even if light is shining on the screen because of the high contrast of the theme. I don’t quite agree with this reviewer with his “fecal brown” statement about the theme. It is more black than the traditional ubuntu orange and the orange that is there is more of a bright orange than a fecal brown.

Netbook Remix with MS Office

Netbook Remix with MS Office

Awesome things:

The netbook launcher is probably the best part of this entire package. It works well, looks nice, and doesn’t use very many cpu cycles. The framework they used on this (clutter) really has potential in my opinion and if they keep developing applications for gnome with this framework it will probably become the desktop of choice for ease of use alone.

The app switcher with maximus is probably the second best part simply because it takes advantage of the smaller screen resolution. I originally thought that it would be annoying to have just the icon to tell me what the program was, but it really isn’t nearly as bad as I thought it would be. It is pretty easy to remember where the icon for the particular window is. Another plus is the fact that the titlebars will take up as much space as possible. Even with long window names (movies on Tudou…looong names) I have not yet managed to get the … to show up in the title bar.

Not so awesome things:

There isn’t very many things I can really see wrong with this except for one bug in the netbook-remix launcher. Whenever something changes in the menus the launcher will close and not reopen until I restart it using alt-f2. However, since the last update this hasn’t happened so they might have fixed it.

Microsoft Office:

The screenshot above shows my Microsoft Office installation. This took two-ish days to get working. For the longest time I was trying to use WINE to install it, but to no avail. The rpcrt4 dll would never replace properly and the whole thing would hang up on pipe_wait status with a fatal dll error. I eventually decided to use crossover linux and install it that way. It installed on the first try within 45 minutes. So far the only problem I am having with it is microsoft word crashing when it starts up. This isn’t too much of a problem because I only plan on using OneNote on Ubuntu and switching into windows to write papers and stuff if I need to on this computer (I would prefer to use my larger computer for those).