Auxiliary Input for Boombox (or any old stereo)

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I’ve tried multiple times to recycle old boomboxes and stereos using them as docking bases for iPod (or any music player). The success rates where… humm, variable. But today I developed a relatively fail-proof method that doesn’t require strange components or Voodoo to work.

Many thanks to Carl (Crutschow) from Electro-tech-online.com by his invaluable technical advice

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Getting ready

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I’m going to use this old Sony boombox for the experiment. The build quality is far from the golden “Made in Japan” era, but

a) The sound is still very decent

b) The unit only consumes 12 volts – very adequate for swimming pool parties or camping.

c) I got it for free!! (who needs overpriced Bose stuff anyway?)

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This is the main circuit board, the place where we are going to work

The separate circuit board is the power supply, it converts the home 110/220V mains. Don’t touch it.

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The signal

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Get a 3.5 mm stereo cable to connect your music player. Chop one of the plugs (as seen on the picture), only one is required for this job.

If you are too lazy to buy the recommended cable, you can scrap a pair of old headphones: However that type of cable is very tricky to work with, so I recommend reading this post to learn how to deal with it first

Pick a song on your iPod or mp3 player, and keep it ready for the next step.

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Injection!

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Click on the following diagram to enlarge. As you can see, we are going to inject our signal into the amplifier, the “heart” of our boombox. The 50K Pot is a piece that we’ll see later.

Finding the amplifier chip is easy, normally is under a heat sink, or bolted to it.

My amplifier is bolted into the heat sink. But in other models it’s under the metal piece, in that ugly case you must unscrew it to gain access

If your boombox doesn’t contain any heat sinks, Google the name written on the chips to determine which one is the amplifier. Do not confuse “amplifier” with “pre-amplifier”, the second is not the chip we are looking for

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Knowing the right pins

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Now that we found our amplifier, now we need to know which one of its legs is the input. Well I mean “Inputs” in plural, because we actually need two: One for the Left and other for the Right channel (My diagrams only show one channel by simplicity reasons)

Getting this information is very easy. Just Google the name of the chip followed by the word “datasheet“. You will get a nice .pdf  document describing the chip and its characteristics.

Here is an screenshot as example:

Identify the following three pins, this is where we are going to connect our music player

[NON INVERTING INPUT A]       [NON INVERTING INPUT B]       [GROUND]

I don’t want to insult your intelligence, I just say this by liability reasons:

TO AVOID BURNING YOUR MUSIC PLAYER, DO NOT CONNECT YOUR PLAYER INTO ANY PIN LABELED AS

[V+]      [V-]      [OUTPUT]

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Lucky strike!

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When I was about to turn on my PC to search the datasheet, I found the labels INPUT ,L , R, GND on the circuit board. That means no datasheet was required!

I thanked Sony for making my Job easier, and proceeded to solder my wires. Maybe you are lucky too, so check your board carefully.

When you are ready to test

1) Connect the boombox to the power supply.

2)Make sure that you mp3 player is playing, and set the lowest volume possible without muting it.

3) Set your boombox volume at the  lowest possible setting without muting it.

4) Set the boombox on TAPE or RADIO.

If you are suddenly hearing your favorite song, hell yes! you did it.

But don’t celebrate yet, Disconnect the unit immediately. For your player’s sake.

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Remember to Cut the tracks

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At this moment the player seems to work normally because it overpowers the existing boombox circuitry. That’s great, but the existing circuitry is overloading your music player and may burn it.

Don’t panic, the problem is very easy to fix. All you have to do is cutting the original tracks that were connected to your amplifier inputs (yes, both left and right channel tracks must be cut). Do not cut any other track, because they are required by the amplifier to work

Click on the images to enlarge them.

In the drawing below, the solder blob is where the amplifier leg is. The red cable is the one coming from your music player. The track, well you know.

Thanks to Microsoft Paint for the high budget graphics. As you expect, cutting the tracks will disable the Radio and Tuner on your boombox. You can re-enable them everytime you want, putting a switch in place of the broken track.

Now everything is safe to use! 

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Last step: The volume control

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The sound is great, however, you will notice that the boombox volume control is not working, and the player volume control is exaggerated. This is because the player by itself is too powerful for your amplifier. So you need to build a new volume control. Don’t worry, it only takes two minutes!

All you need is a “gang potentiometer”. Its just two normal potentiometers linked by the same shaft – one for each channel, avoiding you to adjust two different dials every time. You can buy this part on any electronics store, or if your electronics ability is good, scrap it for the same boombox.

This is how a gang potentiometer looks like. I numbered the pins to avoid any confusion.

Follow this diagram. The “input” is the cable coming from your music player. The output is the cable going to the amplifier. Number 3 pin is connected to ground

Diagram property of http://www.beavishifi.com/articles/Volume_Control/

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Finishing the job

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Open a hole to install your volume control if you need to. Don’t mind my bad taste, I was in a hurry.

I though it was funny to pass the wire through the cassette deck, and using it as the player compartment.

Reassemble the unit, and pack your bags for the trip. Hell yeah!

Downsizing old devices – The Basics

A good friend of mine came to my home asking for help with his old stereo. He wanted to downsize it, as part of a home improvement project.

Before continuing, keep in mind that this guide is just an example intended to inspire you. It doesn’t describe how to downsize EVERY electrical appliance in your home, and obviously, the principle cannot be applied on all devices (specially old TV’s haha!)

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Just air

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Low-end stereos (like the one my friend brought) are basically a huge plastic box mostly filled with air: Removing the air will magically decrease the size. Middle-end stereos have a more complex and decent construction (they include huge transformers and heat sinks for example), and hence they are harder to modify.

In either case, strip the obsolete CD player, Tape Decks and other innecessary accessories: They are not required anymore, because your iPod will replace them.

At this point the volume reduction was great but not sufficient, so I decided to put the horizontal circuit board upright. I’ll show you that in a moment, but let’s see the electrical stuff first.

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Yeah, the electrical stuff!

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Relocating a circuit board will break the electrical connections. Luckily  these connections are very easy to extend

For example this function switch

First desolder it

I find the ribbon cable very good for the job. You can geit it for free on old computers, it’s used to connect the hard disks.

Stripping the plastic cover out of ribbon cables was a pain, until Ideveloped this very effective (and pollutant) way

My lighter ran out of gas at 3 AM

Despite the dramatic flame, the isulation will be warm to touch. Use your nails to pull it out

Ta dah!

The switch after soldering

And repeat the procedure as required…

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The hardware stuff

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This is a very project-specific problem, so I cannot provide you specific step-by-step.

In my case this is my FM dial, it was linked with a set of gears placed 90° apart…

…So I just glued both gears together, and it’s done.

To keep the circuit board in vertical posicion, I have recycled the original structure.

Cutting the pieces is very easy with a heated knife.

You can experiment with hot glue, and if the result is good, use superglue to place everything on its definitive position.

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Almost finished job

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As you can see, the only remaining steps are cutting the unnecesary base and making a new (smaller) box.I rely on my friend to do this part of the work because he has better equipment.

So I will upload the pictures of the final product soon!

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EDIT:

My friend never completed the box, so I did a cheap (and a bit exaggerated) Photoshop trick to give you an approximate idea of how it will look when finished.

Bicycle Stereo 2011

I have decided to drastically improve the construction and finishing of my projects. The first priority was the bicycle stereo.

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The old project

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Too much weight and complexity, for such simple task

The wiring looked like a home-made bomb!

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Now

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Velcro is awesome to snap the music player into the frame

As you can see, the speakers are now hidden.

All the audio wiring is running through an old USB cable

If you remember the previous project, the speakers where placed “bare”, without any enclosure. Hearing decent quality sound was pure luck. Using a couple of Sony-Erickson sealed* cellphone speakers gives much better sound quality, less weight and better appearance.

* On the old project, water proofing of the speaker cone was done with transparent paint. The new cone material don’t seem to require that.

The 12V sealed acid battery was removed, now all the work must be done by the user driving the generator.

The new generator rubber wheel reduces the squeaking noise

The rest of the setup (the amplifier box) is pretty much the same, so posting it again doesn’t worth it.

Laptop Battery Rebuild – Why it failed

The problem: Battery still appears as “empty”, even if  I charged it all day long.

For the last six months, I been carrying a 3 meter extension cord on my university backpack. Why? Because a replacement battery for my DELL 6400 laptop costs $325.000 pesos. To get an idea of how much it hurts, think about earning $325 dollars (just for informative purposes: 325000 COP = 170 USD)

However, the net is plenty of stories about ¿easy? and ¿successful? laptop battery rebuilds, so I gave them a try.

Edit: As you already guess, this procedure failed. But I posted it anyway because it teaches how to open sealed plastic cases, among other li-ion battery stuff

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Open it

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Almost all people who tried and documented this hack ripped the battery case open. There is a more “glamorous” way to do it.

First step is heating an utility knife. If the grip ctaches fire, you are doing it wrong

Cut as shown, following the existing separation between both covers. Watch the depth!

From time to time, use a flat screwdriver to separate the covers. Go easy! If you find resistance, switch back to the knife.

Keep going, and going, and going

It’s obvious, don’t cut over the battery contacts!

One last cut, and Ta dah!

Hell yeah

A nice old feature: LED bar display gauge

Here’s a view of the whole device, notice the circuit board.  The two black wires are a thermocouple. Three cells are wired in series, then the two resulting groups are wired in parallel.

Now it’s time to buy new cells, and we are ready to go!

Or perhaps not.
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Damn smart Batteries

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On old battery packs replacing the cells fixed the problem. But in my case the cells are fine, there is an evil intelligence inside the battery that labels them as inoperative. Its called Smart Battery

Yeap, the battery gauge. The chip keeps track of the the manufacture date, Cycles Count, Full Charge Capacity and Permanent Failure Flag. I’ll explain each one of this items

Full Charge Capacity: How much current the battery can provide. I’ve explained that in layman terms on this post. The capacity drops over time, as you are about to see.

The manufacture date: For every year under storage, the battery losses a percentage of capacity

Cycles Count: Every time the battery is fully charged and fully depleted, 1 cycle occurs. More cycles mean less full charge capacity. After certain number of cycles (200-500) cells will fail.

Permanent Failure Flag: Li-Ion Batteries are very emotional. To keep them under control, the “brain” permanently disconnects the whole pack if one of the following conditions occur:

• The cells over-discharged
• One of the cells gets shorted and consume its neighbors.
• Too much cycles have been reached.

This is actually a good feature: For example, recharging a fully depleted Li-Ion cell without the Smart Battery system may lead to explosions and other unfriendly results. But the bad part is, good cells can be labelled as bad.
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What can I do?

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If you don’t have fancy equipment like an SMT soldering station and a EPROM programmer, nothing. I’ve checked the datasheet of the BQ20857 and the BQ29311PQ chips, and they are very intelligent (or I am very dumb). This is a job for a professional battery rebuilder, so I gave up.

Remember:

• Don’t buy old batteries, even if they are cheap as dirt.
• Don’t leave them fully charged. 40% is good for storage.
• Li-ion batteries don’t develop memory effect. Constantly using and recharging a lithium ion battery does not shorten the battery life more than normal usage would.
• Don’t allow the battery to discharge completely.
• Don’t expose them to high temperatures. All right, the computer will overheat them anyway, but don’t make it worst leaving the computer on a car under the sun.

Here are some interesting links

http://www.buchmann.ca/article21-page1.asp – A more serious explanation of the SM Bus

http://en.wikipedia.org/wiki/Smart_battery_system

Turn a Desktop Computer into Portable

Today, blog visitor MacMarty15221 commented about his plans to build a Windows PC on a small case, to troubleshoot his customer’s hard drives “on the field”.

Thanks to his comment I remembered one of my favorite projects, made some years ago (2007). I hope you can get ideas and inspiration for your personal project.

Note the speakers at each side of the screen

Keyboard and mouse are stored separately

DVD-RW Unit

With disc removed

This unit is not battery operated, but that problem is compensated by its high power, low price and extremely easy repair/update. Buying a laptop with similar RAM / processor is very expensive, and repairing or updating it is a nightmare.

Aperture Laboratories, hell yeah!

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Project Background

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Back in 2007 I desperately needed mobility, but I had no money for buying my own laptop. That’s why I decided to modify my existing desktop computer.

Ingredients:

- Desktop Computer

- LCD Screen

- Suitable case

Various:  Screwdrivers, soldering iron, dremel, zip ties, utility knife, six pack of beer, music

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Construction: PSU Modification

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The first obstacle was the power supply, as you are about to see

The problem is pretty obvious: the fan is horizontal, but the only free air available is at the top.

So here is my patented, amazing, magical solution! (just kidding, you know)

Tah dah!

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How to cut the case

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The case was a very nice wood toolbox. The interior was covered with foam, and the exterior with a very thin (almost insignificant) metal layer .

Measure how big the holes should be.  Mark with a sharpie

Proceed to cut. The dremel is the most clean and predictable method, but if you don’t have one an utility knife will work.

Here’s another example

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LCD Modification

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This LCD screen is special for me.  I was the first among my friends to have one, back in 2003. Compaq 1501 TFT

Cover removed

The only problem with my specific screen was the VGA female plug. It was too tall to fit

After many unsuccessful tries to desolder the plug,  I just destroyed it and soldered the wires in place. I hope you’ll choose a more decent method

The electrical connections are very simple, but I can expand the topic if you need more help

PS: As december 2010, the screen is still working. Backlight sometimes blink, but damn thing is strong like a tank!

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Mounting the screen

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FELA helped me with a very clever and elegant method to hold the screen in place. Thank you my friend!

Check the height before closing the lid, you don’t want to smash the LCD into the other parts

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The cover

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The best way to cover the systems is a wire mesh.

(Notice the speaker layout on that early build. Very ugly monaural sound)

Finished unit (at that time)

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Improvements

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Well, is not a real “Mark II version”, because I’ve made many modifications and improvements to my computer since 2007.

Mom helped with the cloth, simply beautiful work

As I said, updating or repairing the system is extremely easy.

New ASUS board. State-of-the-art (at 2008)

AMD Phenom X4

One of the most important changes was the DVD-RW unit. I have modified the device, replacing the loading method.

And the rest is history.
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Finished work

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This is how it looks today, hooked up to a bigger modern screen.

If you have any question feel free to leave a comment

Laptop Charger plug repair (how to)

Thanks to their very “honest” design, laptop chargers tend to break relatively easy. The plug internally detaches from the wire, and momentarily works when the user bends or twist it. The solutions are simple: Buying and replacing the plug, or buying the whole (damn expensive) charger.

But if you don’t have time and money for that, I offer you a better, third option
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Wait!

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This repair only works when the plug is the problem: Charger LED is lit, computer doesn’t charge, but it does when the plug is bent or pushed. This tutorial doesn’t explain how to replace the whole cable (i.e. if your dog chewed it), but I’ll make a post about that later.

If the LED doesn’t turn on, I suggest you to check the other cable (the one that goes to the wall) using a multimeter.

If the cable is good but the LED remains off, bad news: maybe the jack detached from the charger circuit board, or in the worst case the charger electronics are fried.

In my example the LED is turned on, so we are ready to go

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Let’s do it

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Cut off all the plastic around the plug. Remember the Headphone plug repair post? Heating the knife will make the job easier. But please, watch your fingers!

REMEMBER THE POLARITY! That means, which wire is connected to the + and the – side of the plug. Do not forget it! or you will damage your computer

Ok, now its the turn for the wire. Cut away a few inches of the end, to make sure the damaged section is gone. Then strip the insulation as shown

Adding some solder to the copper (prior to soldering the plug) will make a better contact.

I say again: CHECK THE POLARITY!

Remove the excess and solder the plug as described on the picture. Very simple.

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Now comes “The Art”

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This is the most important of the post: I’ll teach you my ancient, patented technique. Is not very luxurious, but it’s free. I’m using common hot glue to rebuild the plug insulating body.

The shape grows progressively around the plug

Here’s another plug I did days earlier. Notice that I replaced the cable too.

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Finished Work

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Maybe is not very pretty, but works very good

It’s done!

Virus: My files turned into shorcuts (SOLVED)

Lots of people are having the same problem with a damn new virus, here at my university. It spreads via USB memory sticks or external hard drives, and “converts” all the files into shortcuts.

I say “Converts” because the real files are still there, even if the user is not able to see them.
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Ingredients

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1. A decent Antivirus. If you already have one and the computer is still infected, uninstall it and try another brand

2. The sick USB memory stick, hard drive, etc. (Do not plug it in yet!)

3. An Internet connection to update the antivirus (oh, really?).
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Step 1

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First thing you have to do is disabling Autorun: Yes! the window that pops-up everytime a storage device is plugged in.  If you see the silly window, the virus may have entered into your system.

The easiest way to disabling Autorun is downloading and executing this file http://downloads.pcworld.com/pub/new/privacy___security/DisableAutorun-zip.zip. Say YES when the message box appears. Credits go to Nick Brown and PC World
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Step Two

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Now that Autorun is disabled, proceed to scan your  computer with the updated antivirus
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Step Three

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Now it’s safe to plug the USB memory or hard disk in. The antivirus should catch the worm at this point, but even if it doesn’t keep going with the next steps.

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Step Four

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To remove the virus you will need to actually see it at the first place.

I’ve written the following steps on this Windows XP computer, but the icons are the same on Vista and 7

1. Click on Start

2. Control Panel

3. Pick Folder Options

4. Click on “View” tab

Clear the following checkboxes
5. Hide protected operating system files (Recommended)
6. Hide extensions for known file types

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Step Five

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Detelete Spotlight-V100, .Trashes, ._. Trashes, Autorun.inf, and everything you don’t recognize as yours. Delete the shortcuts too, because they are part of the infection.

.Exe? Kill it too!

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Step Six (and last)

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On Windows Vista and 7, click on start, and type cmd in the first box you see

If you are using Windows XP, click on “Run” first, and type cmd

Now you will see a black window, waiting for your input

Write the code as shown and hit ENTER. Replace X with the letter of your infected USB flash stick or hard drive (in my case it was “F”). Wait a few seconds

Thanks to this site for the commands.
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Finished Work

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Your files should look clean by now

I find this procedure is totally harmless, but hey: I don’t want lawsuits, witchcraft, voodoo, or anything against me. I take no responsibility for any consequence: as everything on this site, try it at your own risk.

Thanks to Wikipedia by the Autoplay screenshot

Spot Welder using two microwave oven transformers (part 1)

There are many ways to holding two pieces of metal together, welding is one of the oldest and most reliable. Making a strong weld is an art by itself, and requires proper equipment and lots of experience. Experience requires training, but training is boring as hell if you don’t have any equipment to practice with. There are many types of welders available: Arc, Tig, Mig, Spot…

Picture showing a commercial spot welder unit – from Wikipedia
As I have very short experience, I decided to start with the simplest and somehow most predictable model: the spot welder. The first minute of the following video will explain you what am I tallking about:

Yeah I know, the freaking video is plenty of Puns! but What can I do?

To make our homemade spot welder we’ll reuse two old Microwave Oven transformers. The modification is very simple but requires intensive physical work, so get a six pack of cold beer and lots of patience.

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The ingredients

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I stupidly deleted the step-by-step pictures, so I’ll do my best to describe the disassembly process with the surviving photos.

There was a jungle of wires and cool things inside the microwave oven (I scrapped them before taking the picture, sorry).  The Box on the center of the picture is the transformer, the most important part for our project. But Wait! DO NOT TOUCH ANYTHING YET!

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Hight Voltage Discharge

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The microwave oven (even unplugged from the wall outlet) stores a lethal amount of energy. Locate the rounded box (called Capacitor) and discharge it using two flat screwdrivers connected with a thick wire. THE SCREWDRIVER GRIP MUST BE PROPERLY ISULATED. You will hear a popping sound when the capacitor discharges.

Now when the danger is gone, you can happily scrap everything: The electronic timer, switches, cooling fan and wires are great, but the most awesome part is the rotating tray motor. Turns slowly, and it’s  very powerful. I’ll post a little project using that motor later

Hell yeah

Obviously, don’t forget to take the transformer! it’s the basic part of our welder
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Transformer Modification

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Ok, now we have the transformer, but we can’t use it for welding yet.  We should replace one of the windings, so instead of poducing 2000 volts and 2 amps the output will be 2 volts and hundreds of amps.

On the picture you can see two MOT’s. On the left is “before” the procedure, “after” is on the right

First step is identifying which winding is useful and which is not. As you can see, there is a “Beige-colored plastic thing” covering one of the windings (either primary of secondary, depending on the model). Carefully cut away a piece of the beigé plastic and look.

Using my ultra-high budget picture editor, I’ve colorized each one of the transformer’s windings. Yellow is the primary, Blue is the secondary (under the plastic thing) and the Red wire is the Tertiary. Secondary can be easily differentiated because its made of a much thiner wire than the primary.

PRIMARY WINDING MUST BE PRESERVED! Do not hit, cut or scratch any part of it

Don’t be stupid like me: WEAR EYE PROTECTION AND DUST MASK! A nasty cloud of copper and insulating material will come out. That thing is still itching on my eyes.

Secondary winding will be the first to die, a saw will work great. Keep the tertiary during the process, as a “shield” to cover the primary.

As you can see on the top of the previous picture, transformer’s base may interfere on the path of the saw. Bend it if you need to, and continue

Another method that works well is using a chisel. But be very careful, one hit on the primary and party’s over

A zoom-in of the “chisel” method. Don’t be tricked by the picture! Wires are much thinner, but there are thousands of them! IT’S HARD AS HELL. Personal advice: If you begin to feel frustrated, stop and get a cold beer.

After cutting a side of the winding (as shown) it’s time to go to step B

And this is step B: using some kind of square rod, hammer the winding to push it out of its place.

Pieces of copper will pop-out from the opposite side. Ok, “pop-out” is an exageration, you must hit really hard to make them move a few milimeters each time. I repeat: If you begin to feel frustrated, stop and get a cold beer.

At the final moments of the battle, a big chunk of copper (still maintaining the rectangular-shape) will come out

This piece came from the other transformer: See how densely packed the damn copper wires are!! seems like a solid copper rod!!

It’s a pretty decent amount. Donate the copper to a less fortunate person so he/she can shell it

Cut the tertiary winding using a pair of pliers. It’s just a few turns of wire, piece of cake.

Tertiary winding is history

Last but not least: There are some metal tabs  resting on top of the primary winding. They are called Shunt, do not remove them! If the shunt fell off during the secondary winding removal put them back in place (never happened to me, but you just never know).

PS: Shunt is not green, I’ve colorized it using my ultra-high budget picture editor

My friend Luis Antonio holding the trophies at the end of the day. Remember to clean the remaining dust and debris with a soft brush.

I know there are hundreds of homemade spot welder tutorials on the net. But as I’ve suffered some delays and frustration thanks to pooly explained step by steps, I did my best to spare you that annoyances.
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Electrical Work

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First step is welding a pair of wires on the primary winding terminals. Connect each transformer to the wall outlet, one at the time. If a soft hum is heard, everything is working. If no hum is heard, or the circuit breaker trips and the lights go out, discard all of the following reasons:

1. The connections between the transformer and mains are loose. [Check them]

2. Too much current, the wall outlet was already overloaded. [Find another wall outlet]

2. The primary winding is shorted or open. Maybe the transformer was wrecked before you bought it [No solution]

I was upset because NOBODY on the net knew how much current does a Microwave oven transformer draw under no load.

Answer: A microwave oven transformer draws 3.8 to 4 amps without load. 4A x 120V = 460 watt. Damn!

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How to test the connections

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As you already suppose, we’ll replace the missing second winding with something: a single turn of heavy wire. However, bending #4 AWG wire is a nightmare, so its better to use a tinner wire for testing.

My mains are 120V.  A single turn on your MOT will provide you 5 volts. Two turns 13V. Three turns 21V. We only need 2 volt or so, one turn is a good approximation.

Ok, I’ve connected my two transformers in series. That’s how it shouldn’t be done.

Now in parallel. 5 volts output: Perfect!

Now imagine this situation: Transformers work well each one alone, but when you connect them in parallel the result is zero volts. Why????

Your transformers are “cancelling” each other. No problem, very easy to fix: Take one of the MOTs (no matter wich one) and just reverse its mains connection.

When you are happy with the results, mark the mains connection polarity on the MOT body (Fase in spanish means Phase, or Live).

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Using the real wire

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Time to replace the crappy test wire with the real one. Most tutorials recommend #4 AWG wire as minimum. Getting that gauge may be easy on North American hardware stores, but here is really hard. My solution is using a nice 3×8 AWG + 10 wire, a gift from the power grid maintenance workers.

Not as good as a “solid” #4 AWG, but I hope it works

You can see the three #8AWG wires and the fourth #10AWG

Don’t forget to get some copper tubbing for the jaws!!

To be continued…

Minipost: Poor man’s Fuse (Reusable)

If your projects tend to explode, avoiding fires and blackouts is a priority. Using a dedicated circuit breaker for the workbench is an obvious safety measure, but sometimes is not enough: The short or the overload may not be enough to trip the breaker, so the circuit keeps energized. The result? Nasty overheating and smoke!

The solution consist on a pair of nut and screw, holding a wire filament. The washers are optional, they’ll make a better contact.

The screws are in series-connected with a wall outlet and a switch.

The circuit is so simple that it hardly requires an explanation. Just note that the bolts and switch are in series with the LIVE wire.

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Using it

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When an ill-circuit is plugged in, the results are pretty predictable: the wire filament will explode. However, that small spark and clicking noise are nothing compared with the flash and loud bang coming from a full sized short circuit (your circuit breaker will thank you for that too). To get even more safety and quietness, put a removable cap over the screws.

To “reset” the breaker, cut another piece of wire filament and fasten it on place.

Make sure that the switch is OFF before plugging a suspect device in, or while changing the burnt wire filament!

PS: I know that this design constitute an offense against usability, ergonomics and good taste. Don’t blame me, I was on a hurry! I’ll make a replacement someday

Domotics vol. 1 – Computer Control

For the average Joe, “Controlling stuff using computers” sounds like a very Geeky and boring topic. That is because these systems are usually found on factories or inside complicated equipment, hidden in black boxes. However when computer control jumps to everyday life and works along with industrial design, the result is outrageous!

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In this post we are going to make a very simple version of the system. Of course, forget about wireless and iPhone capabilities!! I’m by no means an electronics expert. But I hope that once you understand the basics, you can easily try more complicated and capable systems (beyond the scope of this blog).
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Ingredients

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Ok, enough Prologe. First ingredient you’ll need is an old computer. I’ve choose a PC running Windows XP.

Check the back panel. The computer should have this connector, it’s called Parallel Port. It was used to connect Printers, Scanners, and similar devices before the USB technology came out. As you can easily guess, is obsolete by today’s standards.

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How does the port work (in layman terms)

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I’ll give you a very simple explanation. The holes (technically called pins) are numbered from 1 to 25. Watch the drawing!

The computer program can turn each pin ON or OFF according to the needs, just like switching a lightbulb.

An external device (an old printer for example) is constantly cheking the port to know what the program wants to do.

Each combination of pins turned ON or OFF means an specific message for the printer, like:

- “Print the H character”

- “Print the I character”

- ”Print the ! character”

The communication is bidirectional, the printer may also send information to the computer using specific pins.

- ” DUDE! I’m out of paper!”

But we’ll talk about that on another post

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Controlling the port

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The port can drive other devices than printers, but Microsoft Word will never allow you to do that:You will need a custom program to turn each pin ON or OFF.

I’ve made my first tests using a great program written in Visual Basic 6.0 by Josh Gaby, here is a link to the code. I know VB is old as hell, you are (obviously) free to use any alternative you want. For example, you can find a C++ alternative on the same website

To see the results on the real world we are going to use a couple of LED’s. Make sure they can withstand 5 volts (attaching a in-series resistor may be a good idea, but in my case it wasn’t necessary).

Snap your LEDs anode (+ leg)  into any of the data pins numbered from 2 to 9. The cathode (- leg) can go into any of the ground pins, ranging from 18 to 25.

Turn ON or OFF your desired pin…

Hell Yeah!

Very easy.
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Controlling small devices

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All you have to do now is replacing the LEDs with your microwave oven, dishwasher machine, 10000 watt stereo… NO, WAIT! is kidding. Attaching any significant load to the parallel port will ruin it.

In order to drive any decent load you need to use a transistor

This circuit is very good for flashlight bulbs, toys, and stuff like that. The transistor amplifies the small signal coming from the parallel port, and uses it to turn ON or OFF the device.  The load should be connected to the third leg (collector) of the transistor.

Controlling 8 different devices require 8 eight independent circuits, each one connected to its respective Pin (that’s why you can see eight transistors). I’ve added some LED’s to increase the “hi-tech” apparency, but that’s optional

This circuit requires 5 volts from your computer power supply (check the schematic). You can get them easily from any spare molex inside your PC, choose the red wire.

I strongly suggest you to cover the other unused holes (black-black-wellow). You may become distracted and plug the circuit into one of them… not funny

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Controlling mains power

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All the examples shown here are a description of my own project, you are free to use any method you want. Whatever you do, you MUST use proper materials and follow your country’s electric codes. Please check the liability section of this blog.

The transistor described on the previous schematic is used to drive a Relay. Pick the adequate voltage and current rating for your load!

PS: The matches shown on the picture are just for size comparison

I’ve connected my circuit in series with the wall switches.

I’ve (temporarily) mounted the circuit inside an old Playstation case. As you can see, there is plenty of room inside to add the remaining 5 Relays.

I’ll use a proper case when everything is finished. If you have any questions please leave a comment!

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Expansion

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The parallel port can drive 10, 20, 50, or even 100 independent devices using an electronic trick. If I have time I’ll write about that later

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My personal project

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(REMOVED FOR IMPROVEMENTS) I’ll add it later