Yenya's World

Tue, 31 Dec 2013

PF 2014

I wish a pleasant year 2014 to everyone who reads this blog.

PF 2014

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Thu, 19 Dec 2013

Arduino SCX Digital to USB interface

I have a SCX Digital slot cars set, and some years ago I bought an interface box for connecting it to the PC using a RS-232 serial port. PC then can be used as a timer, lap counter, and race management. Now I wanted to make some modifications to the firmware (it uses AVR Tiny 2313 chip). I have discovered that the author does not sell this version anymore, it has been replaced by a newer version with USB. So I kindly asked the author whether he can provide me the source code for the firmware for the old version. I have got the following reply:

Hi Jan
Sorry, I do not share any of my software.

Well, whatever. It is of course his choice to keep the firmware of the abandoned version for himself. But in the meantime, I've got some experience with electronics and microcontrollers (see my other projects).

Introducing SCXreader, my own SCX-to-PC/USB interface, built with Arduino Nano. It is fully open, including the source code of the firmware. It costs about US$ 6.50, way less than the current SCX-to-USB SEB interface.

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Sun, 15 Dec 2013

Slot Car Tyres

The tyres of our slot cars are not as good as they used to be, so I wanted to buy new ones. However, the local seller has been less than helpful, so I searched the Net. Apart from U.S. slot car supply sellers (tyres for US$ 7.50, shipping into the Czech republic for US$ 25+), I have found this page, so I have decided to create my own tyres. The original tyres look like this:

Firstly, I have created the box for a new mold, using heavier paper with smooth finish:

The tyres are fixed at the opposite sides using dual-side adhesive tape. This allowed me to make a single-part mold only, and provide the pouring and air escaping holes:

The mold is made from OOMOO 30 silicone, bought at I have used parafine release agent to avoid the original tyres sticking to the mold, but I think it was not necessary after all.

The mold removed from the paper box:

Removing the original tyres from the mold. OOMOO is really stiff and soft, my previous experience with Lukopren 1522 silicone is worse - Lukopren would snap off when removing the models so deeply enclosed in the mold.

For the tyres I have used urethane rubber. I have tested two types with a different hardness. The red one is softer - Vytaflex 30, and the blue one is harder - Vytaflex 40. I have used So Strong pigments for making the rubber red and blue. All those materials were also acquired from

And here is the final product:

It is much softer than the original tyres, and a bit looser on the rims (I have not used any glue so far, though). With the original tyres, the best lap time with F1 cars was slightly under 7 seconds. After the short testing ride with the Vytaflex tyres I clocked the best lap of 5.15 seconds, and average laps around 5.50 seconds. Impressive.

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Thu, 28 Nov 2013

A Not-so-New Pet

I have forgot to write about our new pet, so with an appology for the delay, here it is:

Testudo Hermanni Testudo Hermanni

It is Hermann's tortoise (želva zelenavá in Czech). It is about year and half old now. FWIW, we didn't bought it from the pet shop, but from the breeder at

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Wed, 27 Nov 2013

Proprietary Applications

Welcome to the Rant of the month series, today about the proprietary web applications: The Web is more and more becoming a set of isolated proprietary islands, instead of being the deeply interconnected, how to say it, web. Lots of information, and even my friends, are disappearing behind the proprietary systems.

For example, I would like to get news from @whatifnumbers, preferably via RSS, but apparently it is not possible. Twitter used to have a RSS export, but it has been recently disabled. I, of course, have no intention to use a Twitter account (I think I created one long time ago, but I never used it).

Another examples are Google+ and Facebook: how do you stay in touch with your friends who have an account on only one of these systems? (Or none of them, like myself?) I have managed to create a RSS feed of one of my friends' G+ account, but the feed of course contains only the public posts.

We are moving from the world where people develop applications which everybody can install and run themselves (blogging systems, mail servers, web galleries, etc.) to the world where there is only a single instance of an important application, with no possibility to run my own copy.

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Mon, 16 Sep 2013

3D Printer

Apparently 3D printers can nowadays be built for a moderate price, and their quality is improving. Also, there is a project called RepRap for developing open-source 3D printer (including design of components, Arduino as a controller board, firmware, CAD, and host software).

There are too many variants to choose from, so I was glad to discover RepRap Workshop, where it is possible to build and configure the 3D printer Průša i3 from the RepRap project under the supervision of somebody who has already built several 3D printers and has lots experience with them. All the parts and electronics were included in the price of the workshop.

My printer prints correctly, but still needs configuration tweaking. In the last image there are parts of this object from the open source repository of 3D objects called Thingiverse. I have printed it scaled by 0.7, but the other two parts were too brittle and their pins snapped off. I am looking forward to print more objects, for example LED lens holders for my Bike Lights project.

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Mon, 01 Jul 2013

Transparent Internet

The times when the Internet was considered a transparent network, which relayed any kind of Layer 4 frames, as long as they were properly encapsulated in Layer 3 - the Internet Protocol version 4 (and version 6, recently) - are apparently gone forever.

The Network is not even supposed to look inside the Layer 3 payload, yet some core switches apparently handle a particular L7 protocol in a special way. I wonder whether we are now in state of TCP, UDP, and ICMP being cast in stone, and no way of deploying a whole new L4 protocol, or a substantial modification of current L4 protocols (do you remember TCP ECN fiasco, anyone?).

With NATs and firewalls being the integral part of the Internet, the situation is probably even worse. Not only L3 and L4 are cast in stone, but application protocols as well. These times, everybody seems to tunnel their data over HTTP, as this is the only protocol, which can be expected to pass over this mess of NATs and prohibitedly configured firewalls.

So let's hold a minute of silence for the end-to-end transparent Internet, which is apparently gone forever.

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Thu, 30 May 2013

GPS Tracking Systems

I use my smartphone in addition to the cyclocomputer in order to be able to record my speed, and later compare the speeds at the same place amongst various conditions. The problem is what to use for tracking and what for reviewing and comparing the recorded tracks?

So far I record the tracks using Move! Bike Computer on my Android phone. It is far from ideal, but at least it stores tracks as a GPX files which are accessible directly from the flash. It uses 1-second intervals, and as a bonus, it can display the track using Google maps. The drawback is that it sometimes does not switch the GPS on, so it needs to be switched on manually from the Android top bar menu. The other drawback is that while it can send the GPX files by e-mail to the desktop computer, it does not remember the prefered export format (GPX instead of KML for me) and the prefered export method (e-mail using K-9 mail to a predefined address). So sending tracks from my phone for further archivation is not so easy. But at least it can be done. Another problem is the start and end of the track: I usually start this app before leaving home, and stop it some minutes or hours after reaching the destination. The recorded tracks then cannot be easily compared, because their durations vary in the order of tens of percent, even though the real time of activity is roughly the same. The auto start/stop feature of the cyclo computer is much more precise - the GPS always report at least some movement because of its imprecision and noise.

As for the viewer, the situation is even worse. So far the best I have found is Endomondo, (and "the best" here does not imply "good" at all). Endomondo can import the tracks in the GPX format, and display them on top of Google map, can generate the speed and height profile, etc. On the other hand, it is way too skewed to training and fitness (computing calories, etc.), and has way too much useless social features. It also has its own proprietary Android App, which makes sending data to Endomondo easier, but with this app it is impossible to get your own data back in an open format. Moreover, when importing GPX data with 1 second granularity, Endomondo rescales it to something more coarse (tens of seconds to even minutes), so it makes comparing the speed at a given place pretty meaningless.

What do you use for your sports tracking, and how does it meet your data accessibility and openness requirements?

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Wed, 29 May 2013

E-shop Reviews

Apparently at they think that they sell only perfect goods, and don't want people to write negative reviews to some of the goods, even though the description contains plain lies. As an example, we take this 9V rechargable battery. In the description, they say:

The rechargable NiMH battery from GP Batteries lasts up to 5 times longer than alkaline batteries [...]

There has to be some serious magic used by either Mall.CZ or GP Batteries, which causes that the battery rated at 8.4 V with 200 mAh capacity lasts five times longer than an ordinary 9V primary alkaline cell. Apparently the later according to Wikipedia has 565 mAh capacity, and thus stores three times more energy than the rechargable batery from GP Batteries.

I have written a comment along these lines to the Mall.CZ system on May 7th, but it is still not published as of now. So beware of any e-shop which doesn't allow negative comments, such as Mall.CZ. It is interesting that some bigger shops like DX are perfectly OK with people writing negative reviews to some of their goods.

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Fri, 24 May 2013

File Manager

The last file manager I have used was Norton Commander back in the DOS era. Many years after that, during the flame wars between proponents of spatial and single-windowed Nautilus, I have only laughed at them, thinking that the command line was much better. Why would anybody need a GUI file manager? I feel slightly ashamed now, but I have to admit that for the last two weeks, I have also been using a GUI file manager.

I work on various things with respect to cabling, electricity, a new datacenter, and so on in the new building of Faculty of Informatics. The problem with the building specifications, projects, and so on is, that they are stored in the deep structure of directories, with names containing whitespace and even non-ASCII characters (in different character sets), and each directory contains many files or subdirectories with common prefixes shared by a set of files. So the usual tab-completion does not help - it is necessary to actually look at the completion prefix in order to know what character to add next. Here is an example of such a file name, starting from my automount point:

FIMU_GD_SOD_příloha č. 1/!!!_02_FIMU_GD_SoD_Priloha_1_II.A_PD_DVD_PROJEKTOVA_DOK_1.etapa!!!/\

In order to be able to quickly navigate inside such directory tree, I have started to use a GUI file manager. So far I use Thunar, the default file manager in XFCE. It can easily switch to any directory along the current path, and it has bookmarks for fast access to frequently-used directories. I use this feature a lot, because of the main drawback of GUI file managers: It is not possible to descend into a directory, which is an automount point (and which, from the VFS point of view, does not exist yet).

Do you use a GUI file manager?

Section: /computers/desktops (RSS feed) | Permanent link | 4 writebacks

Tue, 21 May 2013

Cell Phone Operators

Few weeks ago I have moved my cell phone number to a different phone operator (don't ask :-). Today, I've got an interesting call:

Caller: "Hello, I am a representative of $my_new_operator, do you have a minute or two?"

Me (thinking about possible problem with $my_new_operator, with payments, or whatever): "Well, only a minute."

Caller: "OK, then. We have a great offer for customers of $my_old_operator. If you move to $my_new_operator, you can save much money."

Apparently the $my_new_operator's representative does not know that I am already their customer.

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Fri, 03 May 2013

Laptop Upgrade?

I've got my laptop, ASUS F3E, in September 2008. So maybe it's time for a new laptop. Last year I have briefly considered buying a new one, but I have found that after upgrading F3E to 4 GB of RAM, 9-cell battery, and a fast solid-state disk (OCZ Vertex 2), then-current models provided no significant improvement compared to my F3E. Is this year's offer better?

There are several problems with my F3E:

What parameters should my hypothetical new laptop have? Of course, it would need to be better than my upgraded F3E in every aspect, and meet the following criteria:

Does such a laptop exist, my dear lazyweb? Or shall I stay with my upgraded ASUS F3E for another year?

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Fri, 26 Apr 2013

Tinyboard: ATtiny universal board

Having learned how to design PCBs, how to solder SMD components, and how to work with Atmel microcontrollers, I wanted to use this knowledge in more projects. I have thought about two or three things which I could do with ATtiny MCUs, but I didn't want to design a single-purpose board for each of them. Let me introduce Tinyboard, a multipurpose 24x50mm printed circuit board for 8-pin ATtiny MCUs (Tiny25/45/85, or Tiny13). The list of features includes:


A Tinyboard with a single step-up converter, MCP1703AT voltage regulator, USBasp programming connector, and unstabilized power input. The MCU itself is on the bottom side.

More details are described in the Tinyboard project page. So far I have built a step-up converter with it, and I am considering using it together with 9V battery (the size is about the same) as a lighting solution for my kids' bikes. The PCB fab allows boards up to 5x5cm size, so I have put two Tinyboards in a single design, receinving a total of 20 tinyboards. So I definitely have spare Tinyboards. If you have a project using 8-pin ATtiny and you are near Brno, let me know.

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Thu, 25 Apr 2013

Re: The Shared Office Printer

PHD comics is as funny as always. What I consider interesting is the last problem - printing on a special paper (a.k.a. the "Print Sprint"). I solve this problem differently:

Usually, such a print job is single-page only. So the easiest solution is to use the manual feed input. Open the manual input tray, print your job with manual tray specified, return to the printer, and feed your special paper into the manual input tray. People usually don't specify the manual tray as input.

Another alternative is when I don't want to research (again) how to print using the manual input tray from the command line. I run something like "sleep 60; lpr myfile", walk to the printer, open the default tray and manual input tray, wait a moment, and when the print job arrives, just select the manual tray from the front panel of the printer.

Of course it heps if CUPS together with the printer can cooperate enough to display at least the print job name (including the hostname) or even the job owners' login name, to be sure that it is really my print job. How do you print on a special paper on shared office printers?

Section: /world (RSS feed) | Permanent link | 0 writebacks

Tue, 23 Apr 2013

LinkedIn Endorsements Again

A while ago, I wrote about the new feature of LinkedIn - endorsing skills of each other. I have publicly stated that this is a nonsense, and that I didn't want anyone to endorse me, and I would not endorse the skills of my connections. Half a year later, I have to say I was right:

My public profile contains several endorsements for things I barely know they exist, for example for a programming language which I didn't write a single line of code in.

Moreover, I have discovered that I am supposedly "following" several things like "higher education", "computer software", or "Masaryk University". I am not aware that I have willingly decided to "follow" these things, maybe LinkedIn has added them by itself (I have clicked on "unfollow", so I don't follow them anymore). Apparently this is another misfeature designed to make it look that LinkedIn network is big and deeply interconnected.

What do you "follow" on LinkedIn?

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