Oct 08

Quick How-To: build a custom Linux kernel (CentOS 6.4 x64 minimal)

How to (re)build a custom kernel on CentOS

There are plenty of how-to's about building vanilla kernel on all types of Linux'es. The top of the search results tell you about "the CentOS way" of building new kernel - using rpm etc. It might be the "right way" of obtaining a custom kernel, but it did not fit into my brains even after few reading attempts :) Hence this simplified old-style procedure, that proved to work well on modern CentOS.

Why?

I needed to get rid of kipmi0 process clogging CPU Continue reading

May 03

Coming soon

Dear friends,

I have to apologize for not posting much on this blog lately. The reason is simple: I am swamped by the development of this site's Russian twin. There are quite some articles coming on MyElectrons.ru, all in Russian. Once that project gets going more or less - I promise to translate/re-write and post most of the relevant articles from there to here. This site is alive! Please subscribe, live me a comment or write a mail.
Sincerely yours,
- Serge Patrushin.

Mar 17

100KHz square wave generator for testing audio amplifiers

 

[Читать на русском]

The musical signal's form does never resemble a square wave. The frequency range perceived by an average adult hardly goes above 17KHz. Hence I do not give a dime to those heated discussions whether it's appropriate to test audio amplifiers using a 100KHz meander signal. But being an electronic engineer in my heart as well as by education and passion - I can assure you that giving an audio amplifier a try with 100KHz square wave test signal can reveal quite some technical qualities (or lack of those) in the design. Overshots caused by negative feedback loops or signal slopes formed by input/Miller capacitances are amongst things that are easier to observe with meander than when using sound-frequency test signal.

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Mar 09

Simple high-quality saw-tooth test signal generator

[Читать на русском]

Honestly, I would not claim that a saw-tooth signal is crucial for tuning audio amplifiers and similar stuff. It's rather a matter of convenience and helps to spot several non-linearities easier than a sine-wave. I've assembled this generator in order to top off the Wien bridge based sine wave generator. Since then I use it regularly because it helps to reveal subtle oscillation issues in amplifiers way better that any sine or square wave can do.

In this article:

  • High quality saw-tooth generator using CMOS 555 timer chip
  • Buffer amplifier stage with nearly infinite input impedance
  • Variable gain buffer with gain from -1 to +1
  • Linearity of professional equipment using budget OpAmp

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Feb 09

Web site backup and upload: rsync over sshfs (GoDaddy or other hosting with ssh access)

Other good people provided ideas for this solution:
notbrainsurgery @ livejournal
Robert @ softwarerevisions.blogspot.com

For some reason GoDaddy jailed hosting does not provide rsync, while it allows ssh user sessions to the host. It's not obvious how to move big chunks of data without "resume" functionality. Even worse for backup needs... Here's one of possible solutions based on my own experience. I hope this post could help someone too :) Continue reading

Feb 08

How did I discover and recover USB key disk geometry (on Linux)

It's relatively easy to screw the partition table on a USB key. I happened to have a quality 16GB USB key that got it all wrong (due to some of my experiments in the past :) - it was presenting itself as 250G drive. fdisk, sfdisk and hdparm all showed wrong disc geometry. I'd be happy to possess a little jewelry of 250GB, but I am afraid we'll have to wait a year or two for these to come. Sure I'd have problems should I try to use it as is for anything...Getting it all right turned out to be very simple - once I found what to do. Continue reading

Feb 05

High Current LDO Linear Voltage Regulator – the sequel

[Читать на русском]

The previous article about a nearly ideal LDO regulator gained quite some interest amongst readers. Meanwhile I managed to build two "barrel" multi-purpose power supplies based on this LDO circuit.

Working Prototype

Casing was always the biggest doubt in my DIY projects. Here I resorted to nice and cheap stainless-steel cans from Ikea with covers cut from a 6mm thick MDF. Perfect solution... to be stuck behind the desk.

120W barrel power supply

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