Fighting with computers

Computers are not always friendly.

Wednesday, October 29, 2008

Enterprise WPA troubles


Two gadgets we've got recently refused to access the university wireless network. The reason is that WPA with an EPA-PEAP autentication server is used on UPV campus. The ASUS eeePC that comes with Xandros Linux does not support that. Alternatively I could use the eeePC built-in VPN to connect to a secondary wireless network, but again, that software did not work either.

The Nokia E71 cellphone does support WPA Enterprise, but contrary to other wifi setup that can be done on the fly, the so called WPA Enterprise is hidden down there in the system configuration menus.

The solution I took for the eeePC was quite radical as I installed eeeXubuntu. There is a special Xubuntu version that worked for me. You create a boot image on a USB flash dish to get it installed on the eeePC. One word of warning though: I you accept to install system updates, each new kernel update will break the Atheros wireless driver (it can be rebuilt later, but it's a manual process).

The solution for E71 was to ask our Computer Center helpdesk. Again, the process was documented on our web, but not very visible when searching unless you know in advance where to look.

Monday, October 20, 2008

Low power arduino


I've bought recently a new Arduino Pro Mini. I was mostly interested on what the minimum power consumption might be when powering it at 3.3 volts. The average current was 5 mA with pin 13 led off. But what it is most interesting is that sleep mode current goes down to 400 microamps (and this is still keeping the red led on). As the red led resistor is 10k I guess the sleep current will go to almost nothing once I remove the red led resistor. That is a very interesting value if you're worried about power consumption for sensor network applications. A CR2032 will last for more than 500 hours at 0.4 mA!

Friday, October 17, 2008

Stippling fun

Have you ever wondered how to achieve a monochome representation of an image using just dots? This is what stippling is all about.

The next question is how this can be done. You might have seen Wall Street Journal hedcuts and they look great, but they are produced by a human artist.

Machine-based approaches like dithering and half-toning work well too, but they are not quite the same as the above.

Google led me to the nice work of Adrian Secord, with the not so suggestive name of Weighted Voronoi Stippling.

Author provided binaries and source code too. Unfortunately it did not work for me. But after contacting the author, who provided me an updated binary that ran on my Leopard iMac. You have a sample image of the input (right) and output (left).

I want to thank Adrian for being so kind of including my suggestion of adding SVG output to his code (and for making his project's code available).

Saturday, October 11, 2008

Fixing Hardy audio problem with Pulseaudio

One of the few problems I've got with Hardy (Ubuntu 8.04) has been a weird audio problem. It looks like Flash plugin and any other application that plays audio do not like each other. So I have had to close Firefox completely to get audio working again in, let's say Rythmbox.

My audio device is Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 02)

I research the problem a bit and I've found three pieces of advice:

1) Install libflashsupport (which did not fix my problem)
2) Restart pulseaudio (that might be done right by killall -9 pulseaudio) or kill gnome-power-manager
3) As suggested here: asoundconf set-pulseaudio (this one worked for me)

Now I can play a song on Rythmbox while viewing (and listening) a video on youtube. Something it was possible on previous versions.

Friday, October 10, 2008

Inkjet vs Laser

Have you ever been interested on the output quality of both Inkjet and Laser printers? I can see many comments on the net about the cost of running the two types of printers. Someone mentioned that HP is making $10 billion dollars a year selling inkjet cartridges (this seems like a lot of money).

I am not worried about the printers' running cost at the moment. A recent project required me to study a few pages of a document. On a closer inspection I realized they were not printed on the same printer. While laser printed documents create well-defined contours, inkjet printers seem to create small ink spikes on line contour (as you can see on this entry photo).

Light reflection properties are also different, inkjet black being non-reflective but laser printed black being slighty reflective.

I'm not complaining about any type of printers as for regular use I think both provide good-enough output. However, it seems it is not difficult to tell which printer you are using just looking closely to your document.

Monday, October 06, 2008

Trouble with ASUS hardware


While my refurbished-at-home Apple iBook is happily running I put myself in the trouble waters of replacing my aging computer. But first things first: a few months ago I bought my wife an ASUS EeePC subnotebook. While it worked out of the box we quickly realized something was not quite right with it, as any minor impact (as hitting the surface with your fingernails) could trigger either a reboot or completely hang the system. After an RMA, the replacement unit seems to be working happily (after I figured out how to get WPA working first; BTW, do the system upgrade over Ethernet connection BEFORE trying to log onto a WPA wifi network whose passphase contains spaces!!).

For my new desktop (replacing an old Pundit-R) I chose a mini tower barebone PC again from ASUS with a new E8200 Core 2 Duo processor. The system works nicely most of the time, however there is trouble: The Marvell Gigabit Ethernet adapter on the motherboard still has some issues with GNU/Linux kernel. Even the Intrepid Ibex beta (next release of Ubuntu) exhibits frequent network lockups. Interestingly I'm only experiencing this behavior on one of two similar systems (though other colleagues with the same Ethernet controller are feeling the pain too).

Lastly, I'm glad my new computer has a multi-card reader. Pundit-R had one too but unfortunately it didn't work in Linux. However, and again another point less for ASUS, mine refused to accept SD cards to be written. I've check my system logs and I realized all the time the card is sensed as write protected, no matter what the write-proctect tab is located. Fortunately I've found a couple of solutions that work: a) tape b) move the tab to an intermediate position.

I'm not yet sure whether network driver problem will go away or I will need to add a known-to-work network card. For the moment, try to stay away from Marvell Ethernet card.

Saturday, October 04, 2008

Google's App Engine


We've got a talk at our university about App Engine by Googler Mano Marks. In short App Engine is Google's alternative to LAMP. And, like Gmail, Google is offering you free hosting for your web-based application (up to certain storage and daily bandwith limits).

Application logic is written in Python, although other languages might be supported in the future. And backend storage is based on BigTable, which does not follow the classic relational model of many *SQL databases. For me these are two changes that may turn some developers down, but the strong point I think is that developers can forget about scalability or availability problems.

While I've created an account and I've downloaded the SDK, I'm only studying the demos at the moment. If you are interested on learning more I think you'll find the video from Developer Day interesting.