Yenya's World

Thu, 31 Dec 2015

PF 2016

I wish a nice year 2016 to all readers of this blog.

PF 2016

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Tue, 15 Sep 2015

Eternal Spring

This year we spent our holidays in the island of eternal spring. I have been to Madeira in 2010 at a conference, and I had only about two and half days to visit something outside the hotel. This time, we decided to spend two weeks there: one week in Funchal, and another one somewhere close to the Northern coast.

Pico Ruivo

We tried to ask travel agencies whether two-weeks trip with them is possible, but the reply was that it would be difficult. So we ended up booking the flight and accomodation for both weeks separately. Surprisingly enough, the price was about the same as with the travel agency.

Caldeirao Verde

We enjoyed the sea, gardens in Funchal, mountains, and of course levada walks. The weather was nice: it was about 19 °C and foggy weather in the mountains, while the temperature attacked unbearable values of 35 °C in Brno. I can highly recommend Madeira, I would say there is still at least another week worth of interesting places for us to see there.

Have a look at a short description (about 25 photos, in Czech), or a larger photo gallery (about 200 photos).

Speaking of photo galleries: I used Photoswipe for the above gallery. It turned out to be customizable enough for my needs. The only drawback is that it does not work well in Fennec (a mobile version of Firefox on Android).

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Mon, 31 Aug 2015

Mission Completed

The project I started long, long time ago and which made a slow, but steady progress since then, has been finished today. Also, this month is a 10 years anniversary of this blog, which I have started in August 2005.

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Tue, 30 Dec 2014

PF 2015

I wish a nice year 2015 to all readers of this blog.

PF 2015

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Fri, 02 May 2014


I bought a model rocket for my children (and myself, of course :-). We have assembled it, and on Thursday, we went out to give it a try.

model rocket

We have found a large field near Hády, and tried the rocket with an A8-3 motor. The weather was nice with almost no wind, and the rocket has returned after a nice flight about ten meters away from the launch pad. I would guess it reached the altitude of 50 to 100 meters. Another try with the same motor type gave a similar result. Then we attempted to use the strongest motor we had, a C6-7.

In the documentation it is stated that with C6-class motors it can reach about 335 meters of altitude. It was indeed something very different than A8-3. The rocket quickly disappeared out of sight. After several seconds, we managed to get a glimpse of it, as it deployed the parachute. However, there was apparently a stronger wind above, and despite having plenty of space in the field around us, the wind has carried it above the forest.

Despite searching for the rocket for half an hour or so, we have lost it. If you visit Hády in the near future, you can look for our rocket around this place.

Anyway, model rocketry is pretty interesting. Our next project is a 3D-printed rocket. We would like to start with something like the disposable rocket (I already have my own OpenSCAD variant of this design, without slanted fins), and move towards a full-fledged rocket with a return parachute, maybe carrying an on-board camera.

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Tue, 31 Dec 2013

PF 2014

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

PF 2014

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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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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, 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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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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Tue, 22 Jan 2013

New GPG Key (please re-sign it!)

My PGP key is almost 16 years old now - it has been created on 1997-03-15. It is a 1024-bit RSA key, which is not so strong by today's standards. So I have generated a new GPG key 4096R/A45477D5. I plan to phase out my other two keys, 1024R/D3498839, and 1024R/F0BEFD45 in the near future, and publish revocation signatures for them. My new GPG public key signed by both old keys is available at the following locations:

The fingerprint of the new key is: B634 17E5 731B 4F42 69FA 57FF 9453 3581 A454 77D5

I hereby ask everybody who has signed some of my previous keys, or who has any means of verifying the above fingerprint by an independent channel (e.g. over the phone) to sign my new key and send me a signature. It is possible to do this in Linux using the following steps:

1. Obtain my public key

gpg --keyserver --recv-key A45477D5

or use another keyserver instead of, or get the key from our webserver

wget -O - | gpg --import

2. Display the fingerprint

gpg --fingerprint A45477D5

Verify the fingerprint (should be the same as above; you can also call me over the phone).

3. Sign the key

gpg --sign-key A45477D5

4. Export the key

gpg --armor --output A45477D5-signed.txt --export A45477D5

Now send the resulting file A45477D5-signed.txt to me. Thanks!

NOTE: The plain-text version of this blog post, signed by my old key 1024R/D3498839, is available here.

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Wed, 02 Jan 2013

PF 2013

I wish happy year 2013 to everyone who reads this blog.

PF 2013

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Tue, 20 Nov 2012

SMD Soldering

For the first time in my life, i have tried to solder SMD components (as I have written before, I am working on DYI LED lights for my bike). The component side looks OK, and soldering through-hole components went without problems. The SMD parts were a bit tricky, though.

bike lights board bike lights

I have used an ordinary soldering station with temperature regulation, but the results are not pretty. I wonder what is required to achieve this level of quality (watch from 14:10). One possible problem might be that some components on my board (especially the smallest sensing resistors) are connected to the highest-current and thus thickest paths, which suck great amounts of thermal energy when soldering.

Anyway, from the preliminary testing, it seems that my board works. So far I have found the following problems:

Now it's time to finish the firmware and to start adjusting the mechanical parts. I have already made the front spotlight and rear spotlight, and I want to make a LED string. Any tips about making a waterproof LED string out of 3mm through-hole LEDs will be appreciated. Should I use silicon, shrink-wrap tube, or what?

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Thu, 15 Nov 2012

Printed Circuit Boards

For my bike lights I needed a PCB. Out of several services for manufacturing PCBs, I have chosen Itead Studio PCB prototyping service (the other candidate was Seeed studio). Here are the preliminary results:

bike lights PCB

I have placed my order on October 29th evening (Central European Time), according to Hong Kong post, the package was received by them on November 7th, it left Hong Kong on November 11th, and I have received it today, on November 15th.

They also have an interesting "Open source" program - the customer declares that his design is open source (mine is anyway), they make few more boards in addition to those the customer has ordered, and they send them to their other customers. The original customers gets his orderd boards, and in addition to that, two more boards from other open source projects. I have in fact got their demo board (on the right side), and one open source board (the white one). Apparently, it is Arduino 512KB SRAM expansion board. I currently don't use Arduino, so if any Arduino user is interested in this PCB, just let me know.

Okay, now it's time to take a soldering iron and play more with the hardware :-)

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