Fun with Planets and a DSLR camera

I have a cheap fully manual Dörr Danubia f8/500mm lens that I bought back in 2012 for shooting the Venus transit. Since then I used it to take some Moon pictures also and when I am doing so I tend to use stars to find the correct focus – the smaller the star appears the better the focus.

In June I was out for shooting again. I mounted the lens, found some bright spot but despite all attempts I could not focus it into one point. I was wondering about what could I possibly do wrong until… no, that couldn’t be, could it? Could that spot not be a star at all?

A few pictures and corrections later I was astonished by the fact that I could capture a planet (other than our own, of course) with my DSLR and a cheap lens. Of course, the image quality was bad but, that spot was Saturn.


These pictures were taken directly from the camera, they are only cropped and stitched into one file. A few days later I spotted Saturn again:



And then I checked out Venus…


… and then Jupiter.


And I will not tell you what this is in the last picture:


Actually it is not just the Sun but Venus as well from the Venus transit on 6th June 2012.

All images above were just cropped but not scaled, therefore the size of the bodies can be compared to each other.

And since then I have a new hobby… :)


Pillow fight day 2015, Budapest

On 4th April, 2015 the 7th International Pillow Fight Day was held all around the world. In Hungary the Budapest UP! has organized the event to the Heroes’ Square which was a huge success in my opinion.

I have visited earlier Pillow Fight Days and have shot a few photos there, but now I thought creating a video would be more fun.

When I am making a photo or video I like to in the middle of the crowd. Given this, my 8 mm fish-eye lens and a try at recording the videos at 50fps, this is the result:

When watching it in full-screen with the default HTML5 player the “720p50” option should come up. If that’s not the case try this link or try to download the original video and watch it with your dekstop/mobile player.

This was the first time I used Kdenlive for video editing and I immediately loved its straightforward interface and workflow, also its ease at rendering to file – it is a really powerful yet simple editor, I can only recommend it.

Personally I like the outcome and I think I will experiment further.


Creating a mobile Wi-Fi network

As a part of a somewhat larger project I have been thinking about creating a mobile Wi-Fi network that can be carried around (and later can be extended to a network of multiple routers).

As I already have a PowerBank (basically a rechargeable battery with USB ports to charge a phone on the go) it looked like the ideal solution to use this as a power source. But then after a few searches of USB powered or at least 5 volts powered Wi-Fi access-points that meet my requirements to create a secured WDS (more on this in a later post) seemed to be too high. I found a few of them but they either were ridiculously priced or were given bad reviews.

At this time I realized that I had a good old Linksys WRT54GL router laying around. As this is a fairly common model with a quite favorable hackability factor, I did a quick research and found that this might be the best device for me.


The OpenWRT can be installed on this router and from software point of view it has all the features I want: WPA2 support, WDS (Wireless Distribution System – mesh, roughly), admin interface over HTTPS and is running Linux. Well, this last part was not strictly on the requirement list but hey, a device running Linux is always good to see (and opens up a lot of new opportunities).

On the hardware part I found out that the power adapter says it is supplying 12 volts and 0.5 amperes to the router. I found a few places where they told that just after the power jack there is a power regulator (a switching mode buck converter) that converts the voltage down to 3.3 volts. After taking apart I saw that this is indeed in place. Good thing about these buck converters that the input voltage range is usually wide, I found that it is about 3.7-16 volts, so it is more than suitable for my battery powered operation where the voltage drops over time when connected directly to the battery.

After finding out this wide range of input voltage I reconsidered my battery selection. Instead of using the PowerBank I decided to use a more universal solution – AA batteries. These can be found virtually anywhere and can be used for a lot more purposes when they are not used in this project. Also, hooking up 4 of them gives me 6 volts, but if I need more power then 8 of them is fine as well (giving 12 volts).


Here I used 2700 mAh batteries, 4 of them gives about 13 Wh (watt-hour) power (1.2 volts x 2.700 ampere-hour x 4), 8 of them gives about 26 Wh. If the router is consuming the maximum the original power adapter can provide (6 watts) then I can use the router for 2 hours straight from 4 batteries. But I really doubt that even a peak consumption ever reaches 6 watts.

Unfortunately it seems that the barrel plug power connector is not too stable (or maybe just the one I bought was of poor quality), when moving the router around a little a momentary loss of power (and therefore a reboot) was fairly common. So… as the router was already taken apart, I have soldered a pair of wires to the main board for the power and found a hole on the bottom of the case where I could bring the cable out without having to drill it.

It turned out to be working perfectly in the end.

In my next post I will write about making another WRT54GL mobile and setting up a WDS (Wireless Distribution System) to extend the range of the mobile Wi-Fi network.

VoCore: A coin-sized Linux computer with Wi-Fi for USD 20

In early July I’ve found an Indiegogo project of a miniature Linux powered computer called VoCore.

It is a RaLink RT5350 (360 MHz MIPS24KEc) based board with 8 MB SPI Flash (although Vonger, the creator of the project upgraded to a 16 MB Flash for the Indiegogo batch just because he’s a nice guy) with two 10/100 Mbps Ethernet interfaces, one USB 2.0 interface, a bunch of serial interfaces (UART, I2C, I2S, PCM, JTAG) and over 20 GPIOs. All these broken out to standard 1.27 mm connectors while keeping the size at 25×25 mm!

There is a dock to provide some connectors: an Ethernet, a USB, a micro USB (for the power) and a micro SD card slot – this measues 25×25 mm as well, of course.

VoCore is running the OpenWRT firmware. It acts as an access point by default, running a network called “VoCore” (this is unfortunately an open network (i.e. no encryption set up) so changing security settings as soon as possible is recommended).

Vonger, the creator of the project is running a blog at, he was constantly updating it with the latest status of the VoCore development and production, both bad and good news. Thanks to this it seemed that we were witnessing all the little details, it felt like we (the backers) were parts of the whole process :)

The VoCore can be ordered from If you would like to have the VoCore main board only (with all the I/O breakouts but no connectors at all) it is USD 20, but if you’d like to have the Dock as well, plus a USB to TTL converter (note: this is missing from my pictures below!) to re-flash the firmware it is just USD 45.

I believe that the VoCore has a lot of potential thanks to its small size (25×25 mm) its low power consumption (0.6-1.2 Watts) its flexibility (20+ GPIOs and the whole bunch of connector break outs) and low cost.

I think this is a must have board for any geeks out there who have thought about hacking some hardware once in a while.

Oh, and one more thing: VoCore is open source, both software and hardware. All the schematics, circuits, firmware, 3D model for the shell/case, everything is available to download from the VoCore’s site.


GameBoy hardware hacking: Part 1

In the case of GameBoy and GameBoy Color systems the console itself holds just a really minimal program on the board, the so-called boot ROM (256 bytes long). It does the initialization of the components and the cartridge, also it reads the header part of the program stored on the cartridge and checks if that is valid. (Fun fact: the scrolling Nintendo logo is read from the cartridge and it is really a test to see if the cartridge can be accessed correctly. The logo is then compared to the one stored in the boot ROM to see if it was read correctly, if not that indicates some pins are not working and the CPU halts. This is when you need to blow the cartridge.).

All the other program code (i.e. the game itself and all the instructions to make it work) is located on the GameBoy Cartridge alongside with the textures, sounds and all the rest.

So the cartridge is basically the part of the system, the CPU reads it directly when it needs the next instruction and executes the code from there without copying it to its own memory.

The cartridges usually consist of the following components:

  • ROM: Read Only Memory
    Stores the program code and all the resources needed for the game. It is programmed once and then never written again.
  • MBC: Memory Bank Controller (optional)
    The Memory Bank Controller switches banks of the addressable memory space (32 kilobyte in total). The lower 16 kilobytes are always the first 16 kilobytes of the ROM while the upper 16 kilobytes are switchable between several blocks (i.e. part of the ROM or the RAM). There are several MBCs out there with their own purposes. This is a really long story, I’ll write more about this later.
  • RAM: Random Access Memory (optional)
    This is a readable and writable storage, when a game has high-score list, saved game state, etc. it holds them information in the RAM. This is a standard SRAM so this is volatile – it needs constant power to keep the data alive this is why cartridges with RAM need batteries as well.
  • Battery: (optional)
    The battery provides power for the RAM to keep the stored data alive.
  • Connector:
    Last but not least, all the cartridges have a 32 pin connector that provides a connection between the console and the components of the cartridge.

The interface between the console and the cartridge consists of 32 pins (direction is written from console perspective, out: from console to cartridge, in: from cartridge to console):

  • pin 1 [out]: VCC (+5 V)
    This is the supply pin for the cartridge and its components (i.e. the ROM, RAM, MBC).
  • pin 2 [n/c]: not connected or CPU clock
    I have not seen this pin connected so far but some documents claims this is a direct output of the CPU clock. I ran a logic analyzer on this pin, it showed a high-low pattern alternating at 1.04 MHz (0.46 µs high followed by 0.50 µs low).
  • pin 3 [out]: !write
    This is a signal line that is low when a write request is made to RAM. Otherwise this is high.
  • pin 4 [out]: !read
    This is a signal line that is low when a read reqeust is made to ROM, MBC or RAM. Otherwise this is high.
  • pin 5 [out]: !RAM select
    This line is low when the RAM or the MBC is being accessed. Both of them supports reads and writes. Otherwise this is high.
  • pin 6..21 [out]: address selection bit 0..15
    These bits sets the address that is being written or read in the RAM, ROM, or in the MBC registers.
  • pin 22-29 [out/in]: data in/out bit 0..7
    When the console wants to read from the ROM, RAM or MBC these pins are inputs, their values being set by the remote component. When the console wants to write data these are outputs, set to the data by the console.
  • pin 30 [out]: !reset
    When the console reboots it sets this pin high after about 4-5 ms. This delay is probably introduced to give the clock a few cycles to stabilize.
  • pin 31 [n/c]: not connected or analog audio input
    I have not seen this pin connected so far but some documents claims this is an analog audio input. (I think I’ve read something about a direct sound channel on the GameBoy CPU, but that might be a different story.)
  • pin 32 [out]: GND
    The ground connection for the cartridge and all the components.

In the following posts I will write about the different cartridge and MBC types, and also will post schematics and circuits to build a few different homebrew GameBoy cartridges. Stay tuned.