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 I have discovered that the author does not sell this version anymore, it has been replaced by a newer version with USB.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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8 replies for this story:

Tomáš Pecina wrote: What about the clamping diode?

Myself, I wouldn't go for this. There is a clamping diode between the data pin and VCC, and I don't think it is a good idea to expose it to currents of more than 5mA when VCC is grounded. A lot of heat to dissipate for a tiny little diode...

Yenya wrote: Re: Tomáš Pecina

I do not understand. The data pin is configured as an INPUT pin, so there is no way it can source any significant current when Vcc is grounded (I suppose that by Vcc you mean the Right rail pin). And also note that the diode is not between Vcc and the data pin. Anyway, this configuration is tested, and I have verified there is no significant heat generated.

Tomáš Pecina wrote:

No, there is a protection diode between any pin and VCC of the embedded processor (I don't know which Arduino model you use so I cannot look up the catalog data). If Arduino is powered down, the Zener diode will stay closed and all the current (of some 6 miliamps) will go right through the on-chip diode in Arduino. Take a meter and measure the voltages on R1 and Z1 when VCC=VSS and you'll get a picture.

Yenya wrote: Re: Tomáš Pecina

Ah, I understand now. Two objections: 1) why would I clamp Vcc to GND? At the worst case, Vcc will be left floating, not clamped anywere. And 2) even if I will connect Vcc to GND, the current is limited by R1 resistor, so it would be at most 6.66 mA. Given that ATmega328 pins can source and sink up to 40 mA for each pin, I would guess that even the current between the data pin and Vcc pin of ATmega going through the protection diode should withstand similar currents. 6mA is not so much in terms of ATmega GPIO pins.

Yenya wrote: Re: Tomáš Pecina

One more thing: the protection diode is - well - a diode. Provided that it directly connects the pin and Vcc, clamping Vcc to ground and having the pin connected to +18V via 2K7 resistor would mean that the total power dissipation on ATmega would be proportional to the forward voltage drop on the protection diode. Which is - i guess - somewhere between 0.25 and 0.5 V. For 6.6 mA current, the power burned inside the MCU would be somewhere around 3 mW, which is way less than the MCU normally handle. The rest would be burned at the resistor outside the MCU. So I think even connecting Vcc and GND on the MCU side would not bring any significant problems.

Tomáš Pecina wrote:

1. Wrong. VCC won't be left floating, if the power supply is disconnected, it will power the whole Arduino plus any peripherals you may have left hooked up. Some designs are based on this setup (see, eg, http://hackaday.com/2009/06/27/avr-rfid-tag/). 2. The AVR can sink up to some 50 milliamps, right, but the path is through an open CMOS transistor with negligible voltage, not through a junction, which has some .65 volts of residual voltage on it. I'm not saying your circuit is going to destroy the AVR, only that it is a flawed design and definitely not in compliance with the catalog values under which the chip may be safely operated, ie, something I would never do to any of my three beloved Arduinos :-)

Yenya wrote:

I got a multimeter, unplugged Nano from the USB port (leaving it plugged to the above mentioned circuit. The voltage between the data pin and GND is not very stable, but it oscilates between 0.3 and 0.4 V. Which is well inside the specs: the datasheed says that the maximum voltage on the data pin should be Vcc + 0.5 V.

Tomáš Pecina wrote:

Great! So Z1 is closed and the +18V is sourced, via R1, right into the protective diode, the current trough it being approx. 7mA. My recommendation is to insert a 27K resistor between D2 and the cathode of the Zener, which will make your design safe and robust, with negligible impact on its function.

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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 www.silikonycz.cz. 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 www.silikonycz.cz.

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 www.euzelva.cz.

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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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2 replies for this story:

Milan Zamazal wrote:

I recommend to anyone who cares about open Web to do two things: 1. Look at https://prism-break.org/ for available alternatives; not all of them may be perfectly usable now, but GNU/Linux had its limitations as well when I started to use it more than 20 years ago, it's important to start using actively what's available. 2. Think how you can help to prevent DRM becoming an official W3C standard (disguised under the name "EME"); see e.g. https://www.eff.org/deeplinks/2013/10/lowering-your-standards for some information and I suggest subscribing to the mailing list http://lists.w3.org/Archives/Public/public-restrictedmedia/ (and reading some of its archives). And additionaly, please spread information about those things.

Adelton wrote:

Yeah, it sucks. Today LinkedIn informed me that they remove the RSS functionality.

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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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Gris wrote:

This is quite an old design, I prefer RepRap Rostock, which is much cooler and, in a way, simpler.

Yenya wrote: Re: Gris

Well, Rostock is next on my todo list. Yes, it is definitely a cool design (and with one stepper less). However, I wonder whether the extruder with bowden is strong and precise enough, compared to the one on i3 - directly connected to the hot end.

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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 Mall.cz 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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Vašek Stodůlka wrote:

It is possible in some use cases to "last 5 times longer". When you put alkaline cells to camera, they can last as low as 50 shots, but NiMh batteries about 250. Alkaline batteries cannot produce high current very quickly - so technically your comment may be considered as not true. And there is "up to", which can also 0,5x. :-) But if this is a 9V battery, which you put to some kitchen scale, it will last about few months and alkaline can be there for years. But it is still "up to 5x", so they are right. :-)

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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:

stavba_cerit_dok/01_ZADAVACI_DOK/02_zadavaci_projektova_dokumentace/\
FIMU_GD_SOD_příloha č. 1/!!!_02_FIMU_GD_SoD_Priloha_1_II.A_PD_DVD_PROJEKTOVA_DOK_1.etapa!!!/\
FI_F.3_03_PS 03 SUPERPOCITAC, DATOVE CENTRUM_DVD/\
F.3_03_5 SLABOPROUDE ROZVODY_DVD/F.3_03_5.2.01_PUDORYS 5NP - SLABOPROUD.pdf

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?

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4 replies for this story:

Milan Zamazal wrote:

I use Dired in Emacs. Powerful, text based, utilizing common Emacs features (e.g. bookmarks) and excellently integrated with the whole Emacs environment. I don't know how it compares to current file managers but it used to be much more powerful than anything I've seen in the last century. Considering my recent experience with some popular e-mail clients and discovering how primitive they are I've got some reasons to believe there are still not many file managers comparable to Dired. But does it make sense to use Dired without using Emacs generally? Probably not as environment integration is an important part of file manager usage. For instance, it's impractical to have different sets of bookmarks in a file manager and in other applications or it would be annoying if you renamed a file in a file manager and the corresponding change didn't happen in your editor having the file open for editing at the same time.

Yenya wrote: Re: Emacs

Well, the feature with rename probably does not work when the file in question is renamed by something else (possibly over a network FS), altough it can be partially solved with inotify. Apart from that, I don't want to boot another OS just to use a file manager.

thanh wrote:

I use tc (Total Commander) on windows, and mc (Midnight Commander) on linux/mac, both are very similar to nc. Another plus is that it's not required to have emacs (or vim) to use it ;)

Pete wrote:

I have to admit that I simply use Nautilus in such cases. And immediately rename them all.

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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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Bobby wrote: 360

It is called 360° customer view. They can see everything about you in any of their applications :-)

Bulik wrote:

I had similar experience two years ago (and - I guess - with different operator)

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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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dan wrote:

Some time ago I bought Lenovo X230 and I'm ok with it. It has (or can have) everything you described above except of the screen size, which is less than 14", and MS tax. I believe it can be equipped with a 3-band antenna which allows 5Ghz wifi, but in this case you wouldn't have the webcam. Check the specs to be sure. Optionally you can have a backlit keyboard or thinklight. I have even managed to squeeze in a 16GB of RAM and an msata SSD, along with a regular HDD. Battery life is about 5-7 hours with 6-cell battery, but I suspect that the power management in my system sucks. In windows it's much better.

dan wrote:

I forgot - you may also check out Lenovo X1 Carbon, it has similar specs to X230, but the screen is larger with higher resolution I think. You can cut your vegetables with it :-).

Peter Kruty wrote:

You are describing mac book air in your criteria :). (If I can take the liberty of ignoring 'preferably not smaller than 14"'.

Yenya wrote: Re: Macbook Air

Is it really supported in Linux with open source drivers, or have you took the liberty of ignoring this requirement as well?

honzah wrote:

@Peter Kruty: How is paying the Apple tax better than Microsoft tax? You can at least fight that one, I bet there is no chance to get your OS money back from Apple. @Yenya: Why do you have so small requirements for the display? Every other _phone_ has better resolution these days.

Peter Kruty wrote: mac book air

@Yenya: Oh, somehow I assumed this is solved problem for Intel graphics (not really watching this closely). So, yes I took the liberty too. In general looks like so called ultrabooks are matching most of your requirements. @honzah: Yenya was mentioning not willing to pay MS tax (nothing about Apple). Regarding Apple Tax: I believe this is different situation Apple HW and SW are designed for each other and from same vendor. I don't blame Apple for that, because it works very well for usability. Variety of generic laptop vendors are locking their hw to windows, while we can hardly talk about same tight integration for a user's benefit (and I mean a generic computer user, not someone like Yenya with very specific requirements).

Yenya wrote: Re: Macbook Air

Well, I didn't know that Apple uses Intel graphics - this is actually well supported under Linux. That said, even though I did not mention it explicitly, Honzah is right that for me, Apple tax is almost the same as Microsoft tax. Why would I buy a hardware from a vendor which explicitly does not want me to use it with Linux?

thingie wrote:

Basically, you can have a generic crap with some disastrous 1366x768 display (it doesn't matter if glossy or matte, it doesn't, it doesn't, it'll have faded vomitty colors anyway), they are all absolutely same. Or you can have something more decent, but then, it's either the macbook, or perhaps some more high-end-ish ultrabook.

Peter Kruty wrote: Dell XPS 13

Quite expensive, but you are paying for your specific requirements :) http://www.zive.cz/bleskovky/dell-xps-13-linuxovy-ultrabook-s-ubuntu-dostane-full-hd-displej/sc-4-a-167668/default.aspx

Yenya wrote: Re: Dell XPS 13

Looks interesting, thanks. The specs (even on the Dell site) are shallow, though. No mention whether it has matte display, and how exactly the keyboard looks like. Also, no SD card reader, but I guess this is the price for being so thin. OTOH, I am ok with the cost. But according to zive.cz, it is not (yet?) sold in CZ.

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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:

Tinyboard

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?

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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?

Section: /personal (RSS feed) | Permanent link | 1 writebacks

1 replies for this story:

contyk wrote:

Pretty much the same here. And I seem to follow "IT", "Computer Software", and "Red Hat". Time to change that...

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