Savel brain dump in English!

Laser burn

Administrator — Thu, 29 Jan 2009 08:04:05 +0000

At last I repeated experiment from youtube about burning DVD laser. I dissasembled old DVDRW drive. I noticed small crack in laser diode, so I removed the glass. As open laser is very prone to external damage, keep it from water, dust and agresive liquids. I placed laser diode to some colimator from old laser printer. I pumped power up to max- I have few diodes, so decided to burn it to death.
Best way to tune laser beam is to use black, matte material. I used side of the match box- it is brown, but no shiny spots. Also, phosphor on it make nice little smoke. I recorder this experiment with camera, but as the beam is very shiny, the quality of the image is not very good.

Snapshots from video:

And here is the movie about it (Xvid, ~1Mb):

First Run, double matches.
Second run. Single match.

Current is about 0.5A.

More links form my blog (Lithuianian, still not translated):

Next you can see images of laser diode modification.

Diode before. You can see small crack in the glass.

Diode without front cover. I put small current to it, so we can see small shiny crystal.

So youtube movies:

Class-D amp

Administrator — Sun, 10 Aug 2008 18:02:25 +0000

Maybe you noticed, that new home cinema systems, LCD/Plasma screens, receivers have very small amplifiers. Physically small. But the power output is quite big. And there is no big, heavy heatsinks on these devices. And no big transformers. At a first glance I thought that all this output power is represented in “Chinese wats". But in this case, the wats are real. And these devices are using “digital" D-class amplifiers.

What a hell is D-Class amplifier? It is old-new invention- digital amplifier. “Digital" means only one bit The analog output is made using pulse width modulation (PWM) output. Some sound is converted to digital form using CPU ar special chips and this PWM sygnal is fed to powerfull MOSFETS. Real DAC conversion is made on small inductors near the output.

Here is image of one such amp:

I removed small heatsink from the top of chips. There is no need for big heatsinks as efficiency of such amp is about 90% (acording datasheet).

Here is closeup of the PCB. Note the size of SMD resistors and compare to the size of the chips. Chip is TAS5111 and TAS5112 made by Texas Instruments.

TAS5111 is buwoofer driver. Output of the chip is 70W RMS (@ 0,2% THD+N), 95dB dynamic range. And all this for single polarity 30V PSU (3.3V for logic). Other chip, TAS5112 is stereo amp (two channels) 2 x 50W (@ 0,2% THD+N).

The principle of operation is very simple. PWM sygnal from sound processor is fed to the chip. The chip is driving output mosfets in H-Bridge connection. As there are two PWM channels, the output is connected in full bridge. The chip is full of various protection circuits. All DAC is made on quite small 10uH coils (blue cylinders on PCB).

All amp is 6+1. Total 370W RMS from board sized like a CD box. Heat sink need to sink only 40W of heat during max load!

This particular board is damaged, I didn't examined what is bad is this PCB, I picked up this PCB for weblog ilustration only.

TEO myths and reality

Administrator — Sun, 10 Aug 2008 17:28:46 +0000

This weblog entry is more interesting for Lithuanian readers. It is about our biggest internet provider and the problems related to DSL connection.

Nice title?

I am using cheapest DSL service at home. It is working only on evenings and weekdays. And speed is very slow- limited to 256kbits. But the cost is very low (check TEO webpages for rates).

My telephone line is quite old, and cable from crossbox somewhere in the begining of the street (about 1km from my home) is damaged. There is so called “semigrounded" pair. Sometimes I can hear AM radio in my phone… But I don't use my phone for voice calls, I use it for my DSL connection. Few times I asked telephone company to repair, but due to private property problems they didn't managed to swith pairs in the cable to select better wires.

So I didn't cared about bad insternet connection. I blamed bad, old cable. Until one morning. I started my computer and noticed, that there is internet (in the morning). But must not have any internet at this time. I checked the internet by downloading some bigger file from rapidshare… wow! The speed was incredible and now lags and no “web page not found, no DNS" errors!

After some time I've made this screenshot, the speed increased upto 347 kilobytes per second (2.8 Mbit).

I started all internet leaching software I have. Bittorent and eMule speed was about 90…100 kilobytes per second. (Bittorent log show 1120 kB/s maximum working with eMule at same time). I started these, connection hungry, programs just to test if there is some session limitation. Normaly, bittorent and emule opened too many sesions and DLS connected freezed. Now, no problems at all!

And DNS server is working without any problems. In regular way, sometimes it lost packets and didn't replay to DNS requests…

So I've made decision, that speed limitation software used in ISP TEO.LT is buggy. Also, that I have limitations in session number and this limitation is not stated in my contract!

Same effect I can achieve if I select very expensive “full speed" option in my DSL settings. I receive up to 5Mbit/s speed and no lags!
And don't blame bad cable.

WRT54G/GL

Administrator — Sun, 10 Aug 2008 17:10:44 +0000

WRT54G or WRT54GL is well known Linksys/Cisco Systems wireless router. It is famous for its third party firmware. But be aware, new model sold in shop are neutered, the ROM and RAM size are reduced. Look for version with “L" index. It is rumours, that original router with new firmware became to good and was working better that “professional" models for Cisco company. So they neutered and removed some ROM and RAM chips. All these talks, that they reduced manufacture cost using smaller chips is nonsense. In our days, the price difference between 8 and 2Mbyte chips are very small. And I think is hard to get smaller chips

If you decided to get this router, it is worth to look for “L" version, unless you want to do tricks with firmware or you want to use your solder iron. If you select “L" version, more advanced options will be installed in “basic" router.

There is problem with some of these routers. Some time they hang up. One client was using “G" model with third party firmware, but he needed to reboot device from time to time. I offered him to test my personal router with “L" index, but it hang up too. At my home, this router was working fine. After more detailed investigation, I decided, that there is some problems in power supply and it’s filters. So I opened both devices and checked PCB.

Internal power suply is clasic step-down pulsed PSU. I was surprised, that manufacturer used very small and very suspicious capacitors- all caps were 25V x 220uF. Even in CPU core circuit (1.8V) and 3.3V power lines. I didn't measured ESR, but I think the result could be very ugly.
So I decided to change this caps to bigger ones, from spare computer mainboards and VGA cards.

Here is WRT54G PCB before repair:

There is spare place for 5V regulator?

After:

Input cap is 25V x 470uF, output caps all 6.3V x 1500uF. One additional cap is soldered to empty PCB place. I detected 3.3V in that hole.

Two PCB boards for comarison: WRT54G (upper) and WRT54GL (lower). GL has 5V regulator and bigger memory (Flash ROM and RAM). I replaced all caps.

After this repair, both routers are working fine and no freezes.

Both model use third party, linux based, firmware.

Norton 2008

Administrator — Sun, 10 Aug 2008 16:53:32 +0000

In one company I was forced to install several copies of Norton Antivirus 2008. This was retail version of software in nice boxes, and I needed to enter all registration-configuration data in every computer. At a first glance, everything is very simple, just place CD, push few buttons… And I forgot that it IS Norton Antivirus. First, there were older versions of NAV in computers. Norton antivurus requested to reboot each computer twice for upgrade. And all this reboots require to enter administrator passwords…

Here is the story: go to computer, open nice box, take the CD and CD-key printed on envelope. Place CD into computer and wait for automagic install. No way! Place CD and wait for few minutes (tens of minutes- depending on the state of the computer) and then you receive message, that there is some problems with older version of NAV in this computer and need to uninstall software. Press fix-it. You jump to old version of NAV control panel- and there is RED warning that I need to dowload and install some update to remove that damn software. I killed that process and tried to uninstall software from add-remove-programs. No way, there are other users loged to this computer. And installer exited. I rebooted computer to eliminated logged users, hanguped software and other unknows reasons “not to install NAV".
After reboot, install process continues. Then I need to register to some NAV-Symantec oline service. I don't want, but until I didn't register, I can't continue configuring antivirus… But if you press “Next" ignoring red messages about invalid entries, this “registration" is skipped. After this, antivirus is loaded, and it began to worry that antvirus database is out of date. Dowloading of databases and updated took very logn time (it is not internet connection speed problem). And then… we need to restart windows.

Compared to old (7.x) version of AVG, NAV 2008 is ugly slow, time comsuming, CPU eating, silly designed and bad working software.

It took 50 minutes to install NAV2008 to old Celeron (1.6Ghz, 512Mb RAM) computer!

It is not worth such money…

Small drill

Administrator — Sat, 15 Mar 2008 18:38:55 +0000

I am using small Hobby drill (cheap dremmel tool) t make holes in PCB. Recently I broke several high speed steel drills. I decided to explore, why the drills are broken. After some investigation, I discovered that drill is moving a bit to side. The problem is in the drill grip. Sometimes, one element of the grip is “delayed" and the drill is not centered. When I use flexible steel drills, the drill is flexible enough to compensate the movements. But when I used high speed carbon steel for PCB, the brittle drill is damaged very fast.

I disassembled the drill. Here the image of the parts…

The drill is very simple: Chinese made electric motor, brass axle, one ball bearing and drill grip.

The beauty of laser beam

Administrator — Sat, 15 Mar 2008 18:30:59 +0000

Just small note about the beauty of laser beam image. Laser beam is coherent light- the waves of the light are synchronized. So all theoretical effects of light can be viewed with naked eye. Here is the image of interference- some light is delayed and when the phase of the wave is opposite, the light disappears. Or it is just cool image.

And here is the detail of the image above. It is a pity, that digital camera can't catch the “holographic" shine of the object.

It is unfocused red laser beam. I used DVD laser and some lenses. As lenses are not centered, the image is mushroom shaped. The current into laser is only ~75mA. Total distance the beam had traveled is about 6 meters. (18 feet)

Some jokes

Administrator — Sat, 15 Mar 2008 17:25:04 +0000

This web log entry was written in Lithuanian language before new year. It was just a joke…

My nephew decided to build holographic super computer as his science project. (It a partly true). Here is small glance to the upcoming project- all information about this project is about 15 gigabytes in my hard disk. But later I decided to destroy all information about this project because I want to protect human race. Humans are too young for this technology…

Author of this idea is Henkas. In this photo, the authors is fine-tuning the holographic display.

We even disassembled old computer homograph to get some needed components.

Windows CE

Administrator — Thu, 14 Feb 2008 21:56:35 +0000

I have already wrote about terminal computer I have. I didn't managed to start Windows CE on it. Maybe there were some problems in configuration or something. After some time I received more terminal computer and they booted Win CE without any problem. The only problem was in the hardware- blow up capacitors in the power supply. I changed them and everything is fine.

Terminals booted Win CE and I can see standard blue windows desktop. And some requester about connecting to some server. And nothing more. I checked contents of CF card but all information is “crypted" inside few system files. Somewhere there is all settings and passwords stored, but where? The only solution is to “damage" system settings file to force system to “default settings". I noticed, that if I move (and even place it back) “system.hv" file, windows CE (at least this version I have) will reset to default settings. Or maybe to some semi-default settings. After this file manipulations I see configuration wizard when I boot computer. Then I press “cancel", go to “Start Menu", “Settings" or “Control panel". Find “System" icon, press “reset to factory default". After this manipulation systems reboot to its “virgin" state. Now I can configure system as I want.

I found WinCE 4.2 and 5.0 (or maybe all CF card are already upgraded to version 5). This version of Windows CE have installed Internet Explorer 6.0 without Baltic encoding. Unicode is installed and new web pages with unicode charset (like this weblog) are displayed with proper symbols. But all older Lithuanian web pages with Baltic codeset displayed with mixed symbols.

This is nice and slow fanless internet computer. There are some other software in install like remote desktop clients, file viewers and mail software.

While playing with CF cards and files inside it is important not to touch BLDR file in root drawer.

Contents of my CD card:

2003.04.15  18:38            16.384 BLDR
2007.12.06  20:04    dir          BMP
2007.12.06  20:04    dir          Documents and Settings
2020.01.28  04:38            67.739 EBOOT.BIN
2005.08.20  16:18        15.484.163 NK.BIN
2005.08.20  16:15           308.316 SPLASH.BIN

Contents of Documents and Settings:

2007.12.06  20:04    DIR          default
2001.05.31  12:24                52 default.mky
2001.05.31  12:41           131.072 system.hv
2004.09.08  09:45                52 System.mky

Contents of default:

2001.05.31  12:41           131.072 user.hv

BLDR is the “second" boot loader. First one is in the first sectors of the disk. Splash.bin is startup (boot) screen image. It is uncompressed raw image. eboot.bin- unknown. nk.bin- is the image of windows ce operating system.

Clearing-up the house

Administrator — Thu, 14 Feb 2008 21:37:33 +0000

From time to time I am doing house clear-up. If I didn't this, the house will be full of various electronic stuff. Some of the items maybe sold in eBay or local garage-sale, but some items must be thrown away.

Some stuff appears in the house in very simple way- I need some small part on the PCB, so I pick up whole PCB. And the rest of the board is left in the shelf- maybe I'll use other components in the future. But not now IS THE TIME and everything must go away.

In the picture there is green PCB with big BGA chip, near two gamepad joysticks. This PCB was picked up only for FM75 chip- tiny element with eight pins. I also removed some linear regulators from this PCB: 1.8V and 3.3V. They were used for FPGA breadboard. All other chips like big LG cpu, 28LV320AT flash, LV logic chips, LEDs, 100MHz oscillator and lots of SMD components are trash.

Here is bigger picture of the trash to exam.

Here is the list of the trash: Logitech web cam (old one, slow, low res and low sensitivity. Replaced with new no-name), VFD screen with drivers from DVD, TI DSP board, few gamepads (I removed radio modules), CB radio with broken display panel, computer mainboard, old IBM notebook (I removed only few chip from it), some optical mouses (I was searching for specific chips), one wireless mouse, bunch of small motors (gamepad vibrators), some unidentified PCB, some old DIMM and SIMM modules, old HP 5300 scanner (replaced with new-old HP6300 with better lamps). This is my fourth scanner- and only first one (HP5p) was bought in the shop. All others were picked from the trash. These old scanners are much better than new cheap ones .

All this stuff is found in my room. And if we'll look in to the garage…