• Oscilloscope calibration, what a pain

    Awhile back, I had recieved an oscilloscope from someone. a Conar model 255 solid state oscilloscope. 

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    It worked ok but I couldnt trust the readings from it or even the voltages it displayed. I could get basic wave forms displayed and thats all I really needed it for. As time went on it started acting up. Certain setings would not display, simple sqaure waves had major overshoot …… I could go on with so many of the issues that started to appear. So today I sat down and did the calibration from the manual. What a pain.

    total time spent on it was about an hour and I did the best I could.
    I still need need to buy 2x LM733 and a 741 or a better drop in replacement, also a few capacitors and transistors. But those will have to wait till I am employed again.

    here are a few pics of the internals

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  • The death and rebirth of the Widow Maker

    My freind Rick,  along time ago,  gave me his old PC. It was a P4 in a server case and a huge Dell monitor. He had nick named the duo “The Widow Maker “. It was a fitting name.
    Today that P4 has a new case and a new life at my sisters and is still going strong. But the 100lbs CRT monitor had been dying a slow death for a long time,  and I finally decided to put it down.

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    Instead of just sending it to the recycler, I wanted to get as many parts out of it as possible.
    The Widow Maker had a peaceful death,  the last wish she made was to be reborn in a new form. So i started taking out organs and thinking of how to reincarnate The Widow Maker.

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    What parts did I get out of this beast?  A whole lot of heatsinks,  an AC filter for 120V/250V,  some little glass bulbs,  which I am trying to identify,  a bunch of transformers and chokes,  and the prize find of the day…… a decent size flyback transformer (to be expected in a CRT). Seeing that flyback transformer got me thinking. High voltage = fun!  My thoughts went to plasma speakers or a tesla coil or a HV capacitor charger for a larger coil gun. But that thinking led to how the hell do you drive this thing?

    so I got out my dremal and some scrap wood to make a base for this.
    I just drilled out enough wood for this to sit nice and flat. also for saftey reasons, I needed a non conductive base.

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    My driver I decided, was going to be an MSP430G2231, a generic transistor and a power mosfet (22N50 what i have on hand) a few resistors and a diode. Why did I choose a uC with an adc? I wanted to be able to make a varible PWM drive where I can change the frequency and duty cycle to choose the best combo to get the most voltage out of this device.

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    My first test was to find the pins connected to the primary coil and which one was the feedback coil. On this one it was pretty easy, you can see the coil wires soldered to the pins and you could tell the primary coil by the spacing of the pins.
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    The pins on the right I have no idea what they are connected to, multimeter test reveiled no connection to any other pins and the pcb traces dont give much info either.
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    There are also 2 other wires and 2 other controls that are labeled focus and 2, my guess its for some other part of the CRT that needed HV, but not not as high as the main HV wire.

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    My drive circuit
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    With this setup my mosfet gets very hot, really quickly, even with a large heatsink. Good thing I harvested some large heat sinks.

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    and here is the first video of the testing.

    There is a lot more testing and tweaking to do. More to come!

    As for the code for the chip, its nothing special but it will be coming in the next post.


  • VS 2121 Autopsy

    I was given an Altec Lansing VS2121 powered speaker sytem that was going bad. And I wanted to recycle some of the parts out of it. What I found inside was quite interesting.

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    Here is what I found,
    2 x lm324 quad op amp from st
    2 x tfa9842j single chip 2 channel amp
    and a whole bunch of passive through hole parts (caps, resistors) .
    It is a very simple design. Now I have some decent op amps and a decent size transformer (120v to 15.3v 1.6A) with a nice particle board box.

    Time to start thinking of what I can remake this into.
    Happy Hacking!


  • My battle with Ubuntu 11.10

    I decided to finally upgrade my Ubuntu 10.10 to 11.10 and deal with unity or gnome 3.4. Neither of those options looked promising to me. But change is inevitable.

    The whole process was painless, only a few unnecessary librarys removed. When it all finished, unity loaded up and I got to work, trying to make my desktop productive.
    So I went searching and found this link http://blog.sudobits.com/2011/09/08/10-things-to-do-after-installing-ubuntu-11-10/. It definitely helped, like, getting dvd movies to play. Most of it is pretty good advice and the rest is personal preference.

    My opinion on 11.10, I like it but I have my complaints. For example, gnome-shell or gnome classic, when logging in, is better then unity (I’m not going to get into this Unity just sucks, especially on a 32″ monitor) . Gnome-shell ‘s menu bar, it’s very hard to customize it, I’m still looking for the auto-hide option or the opacity setting. And I still can’t figure out how to add things to the top menu bar like the system monitor graph or even a fortune cookie app. The gnome tweak tool helped a bit but there are still large holes in the setting that need to be filled, but over all it does run on my i5 much better then gnome 2. Time to continue on customizing and tweaking the desktop.
    Next is to upgrade to 12.04 lts.

    The battle continues!


  • Experiments in Home Audio (lm386)

    I really needed a quick amplifier to power a few book shelf speakers. Looking around my ic bin, I found a few lm386s.
    Next I pulled the rest of the parts (1x perf board,  2x ic sockets,  2x 100uf caps, 2x 5k pots,  some wires,  and a few odds and ends) 

    Put all this in a blender, bake for few hours and this is what you get.

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    The results are,  its not  a bad sound. some noticeable distortion at higher levels. More improvements can be made, like changing the output caps to bigger ones,  adding a gain selector….etc.
    But what I have now works. Next a class A amp and other projects.