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December 24, 2006

CD Lamp²

Long ago, I promised a CD lamp, so here it is. It took me a long time to complete it since I had to order some LEDs (actually, my girlfriend bought them and gave them to me as a gift), and to buy some solder.

This is a simple project that requires some skills in cutting and shaping wood and lots of old CDs.

The Idea

To make a nice looking lamp that uses CDs to shade the light. The lamp should be composed of two overlapping columns of CDs sandwiched between identical pieces of wood. It should be very energy efficient and output a reasonable amount of light (which implies LEDs).

  • 6 metal rods (I got them from an old photocopier I found in the garbage)
  • 4 special washer for holding the rods (from the same photocopier)
  • lots of CDs
  • 2 pieces of wood (from an old drawer I found in the garbage)
  • 10 LEDs (6 white and 4 blue in my case)
  • A resistor (for current limiting for the LEDs)
  • A switch
  • A 5V power adaptor
  • A calcium tablets package and a bottle cap (for the switch casing)
  • 4 protective rubber pads.


Trace the layout on the wood. The layout consists of two circles spaced by ~12 cm so when the CDs are centered at the center of the circles, the CD holes don't overlap (while the rest of the CD does overlap). Since I had very small pieces of wood, there was very little room for error (in fact, there was no room for error). I traced the layout using a compass and a ruler (pretty standard), and I cut the wood using a jigsaw.

The lamp is symmetrical so the base and the top should be identical.

It is important to thoroughly sand the wood so it is smooth and nice to the touch. It is good to use a large grit sandpaper first and a fine one to give it a nice finish.

Drill the holes for the metal rods. Four of the rods will hold the exterior of the CDs and should go trough the good. The two remaining rods hold the CDs at their intersection. should not go through the wood (they should be only deep enough so the metal rods stay in place once the the top is in place).

The rods hold the CDs inside the lamp and keep the base and the top pieces of wood together.

The light will be provided by two 5 LEDs arrays in parallel as seen in the following circuit schematic.
I alternated blue and white LEDs for the arrays soldered together in order to form a column that fits inside the CD holes. Remember to use a current limiting resistor for the LEDs (see this current limiting resistor calculator).

The switch should go on the power adaptor wire. I was not lucky enough to have a switch ready made for that propose so I built a case for the switch using a calcium tablet case and a bottle cap.


Place the exterior rods in the appropriate holes on the Top piece and place the special washer at the base. The alternating from one side to the other, place CD pairs until the top of the lap is reached (forming two overlapping columns). The CD pairs are composed of two CDs back to back (the shiny face on the outside).

Then, place the two LED arrays and connect them to the power source and the switch. Make sure the LEDs are pointing to the from of the lamp.

Once the LEDs are in place the smaller metal rods and the bottom can be placed. Fasten the bottom using the washers.

Place some rubber pads on the bottom so the lamp does not scratch delicate surfaces.

The lamp is done. Enjoy!
Note: no CDs where harmed during the construction of this lamp.

December 12, 2006

Creative Commons

Here is a very nice video about the Creative Commons license. If you watch it and click on the ad at the end you'll be supporting the Commons. For more info and more videos about the Creative Commons, visit this site.

December 06, 2006

Quick and Cheap Laptop Lamp

I built this quick laptop lamp some time ago for my mom. It is very simple and requires very few materials.

  • 1 type A male USB plug
  • 1 light bulb (that works well at around 5V)
  • 1 lamp body (I found mine in the garbage)
First, I thoroughly cleaned, sanded, and polished the lamp body (which comes from a sort of old reading lamp).

Once the body was clean and shiny (it was completely black before) , I removed the lamp power connector and replaced it with the USB plug. In order to achieve this, the red (pin 1) terminal must be connected to the positive lead and the black (pin 4) terminal, to the lamp ground.

The lamp is basically done.

Since I did not have the appropriate light bulb for the lamp I had to adapt a bulb by adding a solder blob on its side. Now it fits perfectly.

This lamp won't be as power efficient as the LED ones but it is cheap, quick and very simple to build. Enjoy.

December 04, 2006

Bogotá Rake

A Bogotá (besides being a city) is a very effective lock picking tool. It is surprisingly easy to build and allows you to open lots of locks very quickly and easily. I have been able to open many locks just minutes after having this little tool done (including standard door and bicycle locks).

For this project you only need one street sweeper bristle. You can find these on the streets after a street sweeper passed by. Their rotating brushes leave behind these precious bristles.

First you need a template. I found this very good one from Exodus5000.
You have to print it at its original size (@ 500 pixels/inch) onto a piece of paper, cut it using scissors or some other cutting device, and paste the paper using normal glue onto the bristle (after it has been cleaned of course). You should get something like this:

Then, using a permanent marker paint around it and remove the paper.

Now, use some files to remove all the painted sections until you get the desired shape.

Sand it very thoroughly. It is very important. First use a medium grain sandpaper and the a fine one. In order to sand all the curvy sections, I used a piece of sandpaper rolled around a medium nail. In the end, it should be smooth as ....hum... as something very very smooth. This allows for a fluid motion of the Bogotá inside the lock (important if you want to get the lock open).

I accidentally broke my bristle. With the broken piece I built a tension wrench. it is a bit short, but it works well. If you want one, just bend the bristle (not to much or you may snap it)

For those who don't already know, a tension wrench is used to apply a small tension to the lock while you pick it. See this article for more information.

With these tools you can now start a life of crime. You should be able to open simple locks (and perhaps more complex ones) in a couple of minutes. Simply apply a small tension to the lock (as if turning it with a key) using the tension wrench, and jiggle the Bogotá inside the lock rapidly and randomly. The lock should open in less than a minute (keep trying if it doesn't).

Disclaimer: I do not condone leading a criminal life. However, if my blog does inspire you to become some sort of criminal and you succeed well at it, please share a bit of your earnings with me. After all, you will be doing well thanks to me.

December 03, 2006

Wireless AM receiver

This is the schematics for a wireless AM receiver composed of a tuned amplifier, a AM demodulator, and an audio amplifier.

This is the radio receiver implemented on a breadboard.

I'll post more details soon.


My teammate and I designed an integrated op amp. The circuit is implemented using Gennum GA911 technology. It is built so we can test many configuration (i.e. using active or passive biasing). Se below the circuit layout and some pictures of the resulting chip in it's natural environment.

Active-loaded differential amplifier. This is the first Stage of the op amp, with a 5o dB Gain.

Class-AB output stage. This second stage alows for driving small loads and increases the overall gain a bit (~10 V/V).

Note: all circuit schematics account for the pin capacitance of the packaged IC (Cpad = 5 pF). Also the loading effect of the oscilloscope probe used to perform the experimental measurements is accounted for in the schematics by modeling the probe as a resistor (Rprobe = 1 MΩ) in parallel with a capacitor (Cprobe = 15 pF).

IC layout (done using Electric).

The chip (a.k.a. #5) being tested.

The chip in its natural environment.

A close up on the naked chip. Pretty neat.

I'll post more details soon.

November 15, 2006

1000 Visits!

I know 1000 is not that many visits but it is still a good opportunity to celebrate. This is why I'm hosting a Gmail invites giveaway. Basically, if you want a Gmail invite just post a comment saying so and I'll give it to you. Be sure to include your email.

By the way, if you don't want to get spammed, use trashmail or write your email so spammers cannot gather it (i.e. if your email is example@somehost.com, you can write it as "example AT somehost DOT com").

I know Gmail invites are getting old but I have some invites left and I would like to share them.

November 10, 2006

Bench Power Supply

I saw a long time ago that someone built a bench power supply using a power supply from an old computer. This is why, when I found an old pre-Pentium computer (fully working with Win 95 on it) in the garbage, I implemented this idea.

Bench power supplies (PS) are very handy for testing electronics because they are reliable, stable and secure. It supplies variable voltage in a fairly large range, and detects when you are darning too much current from it or when its outputs are shorting, turning itself off elegantly instead of burning or overheating like some cheap power adaptors. Nevertheless, this kind of equipment cost around 200$ (usually more), which is very expensive (at least to me).

My version is much cheaper, I estimate it costs 8$ (4% of the retail cost). Of course, it has some limitations, but not that many.

Enough chitchat, let's get started.

  • 5 female surface-mount banana connectors (I had to buy them @ 8 for 12$)
  • A computer power supply (from the old computer I found)
  • 2 LEDs + surface mount (I got them from the same computer)
  • A switch (I had it lying around)
  • A resistor (use this calculator to get a value for your resistor)
  • 4 protective rubber pads (they give a feminine touch)
  • A power cord (Duh…)

Putting it together

Of course, my computer PS is not standard (GPC 145-4001), so I couldn’t find its specifications anywhere. So, I did a bit of reverse engineering (poking around) and figured out the pinout shown in this table:
Note: for P7 (P1, P2,... are the actual name written on the plugs) the yellow wire outputs 5V when the power supply is plugged in regardless of it being on or off. Also, when the violet wire is grounded, the power supply turns on. It goes off as soon as the violet wire is not grounded. Finally, the maximum power output is 150W, pretty respectable.

In order to control the power supply and show when it is on/off and plugged-in, I attached the following circuit to P7:

This works very simply: the yellow LED turns on when the PS is plugged to the mains and the green LED turns on when the switch is closed and the PS turns on.

I desoldered all the wires (P1, P2 ad P6) from the PS, leaving just one for each output (5V, -5V, 12V, -12V, and GND). Desoldering them is better than cutting for obvious reasons (less clutter, more reliable, etc). The output wires will be attached to banana connectors mounted on the PS case in order to make them more accesible (make sure the connectors are isolated from the case).

In order to pack everything inside the PS case, I drilled 5 holes for the banana connectors, 2 smaller holes for the 2 LEDs, and drilled and filed a rectangular hole for the switch (I know, it would have been much simpler to use a round switch). Since everything fits very tightly in the case, the holes placement must be carefully planned so the added parts won’t interfere with the PS (i.e. stop the fan, make undesired connections between the components).

The last step is to put everything together and close the case.

The newly born power supply will turn off nicely when you short its outputs or when the load exceeds its maximum power output capacity (i.e. when you plug a big motor or a power tool to it). By combining the outputs (DC) you can get 5V (GND to 5V), 7V (5V to 12V), 10V (-5V to 5V), 12V (GND to 12V), 17V (-5V to 12V), and 24V (-12V to 12V).

As a finishing touch I added rubber pads on the bottom so it doesn’t scratch my desk and I labeled the outputs using a labeling machine (pretty fancy).

Future improvements
I will add a variable voltage divider in order to easily get other useful voltages out of it, such as 3.3V and 9V.

November 06, 2006

Some Ideas

This is a list of the things I would like to build (any ideas are welcome):
  • Chocolate Printer: a printer that uses chocolate instead of ink and is capable of printing 3D objects (I've seen some guy stolen my idead, but thats OK, I don't mind).
  • Vibrating Pen: a pen that vibrates producing funny writing (for children).
  • Electric Bike: a bike that uses an electric motor for propulsion.
  • Frictionless Electricity Generation on a Bike
  • Skype Phone Ringer
  • Faraday’s Torch: the ones you shake.
  • Big Van de Graaf Generator
  • OWI 007 Computer interface
  • Weather Cube: a transparent cube that emulates current or future weather on its inside (uses internet weather information).
  • Wooden IPod Case (nano)
  • Foldable Bike Trailer
  • Lock Picks
  • Binary Clock

October 13, 2006

La Cucaracha

Update: La Cucaracha has got lots of attention lately (mainly thanks to Alan Parekh from HackedGadgets). I found some of its cousins built by 7 year olds. See them at ArtBots Robots.
This is a small and very simple robot that requires no electronics. It is inspired on La Coccinelle. They both work according to the same principle, but their bodies and wheels are different. Also mine uses rechargeable batteries so I don’t need to buy new ones after just a few hours of usage.

  • 2 big plastic bottle caps (much like the PC Thermometer)
  • 2 Wire ties
  • 1 screw
  • 2 DC Motors
  • 2 toy wheels
  • 1 switch (a small one so it fits on the bottle cap)
  • Some cables
  • 1 Cable holder
  • 1 Rechargeable battery pack w/ charger
  • 1 3.5 mm audio jack (male and female)
  • 2 paper clips (regular size)
  • 2 SPDT Switches (commonly found in printers)

Main Idea

The idea is to construct a robot that can move around and that will backup and change the direction of the motion when it hits an obstacle.

Putting it together
  1. Cut two diametrically opposite holes on the side of the caps so the motors fit in there. Chose one of the caps as your base cap (the one thats goes on bottom).
  2. Pierce two small holes on the top of the base cap in order to tie the motors to the cap using the small cable ties.
  3. Cut two more holes spaced by about 1.5 cm so the switches fit in tightly (seeing the pictures help visualizing this).
  4. Drill a hole in the center of both caps with the same diameter as your screw.
  5. Install the switch and the female audio jack on the top bottle cap.
  6. Connect everything together as shown in the circuit diagram. I used the audio jack to make the charger connection. The charger is simply a 3V power adapter connected in series with a diode in the + terminal.
  7. Solder the paper clips to the SPDT blades and add a little solder blob on each paper clip end so they look more like antennas.
  8. Test to see if the circuit works properly. When the robot is switched on, both spindles should spin so it goes forward. If an antenna is pushed, the spindle on the opposite side (left spindle if right antenna) should spin backwards.
  9. Fasten the motors to the base cap using the cable ties and secure the other cap on top of it using the screw. Also secure the cable holder using the same screw on top of the top cap, this serves as a battery holder.
  10. Insert the toy wheels on each motor spindle. You can also add a piece of plastic for stability under the base cap.
It’s done! Now you have a small robot that will go around your house bumping on whatever is on its path.

October 11, 2006

Coming Soon

Some projects I will be writing on soon:
  • La Cucaracha, a robot without electronics
  • Cheap Bench Power Supply, see this picture
  • Laptop USB Lamp
  • CD Lamp², the obvious evolution of the CD lamp
  • Cornstarch Pet, a small project based on this experiment
  • Ultra Cheap XBOX USB adaptor.
  • Skype phone ringer.

October 08, 2006

Make Your Girlfriend Happy For 0.25$

I saw in this site (try this one if the link is broken) that we can build a coin ring using a spoon, a drill, a Dremel and some metal polish. Immediately, I wanted to do one.

  • An ordinary 0.25$ coin (Canadian in my case)
  • Lots of patience
Making it happen
Warning: your family and specially your dog could become agitated if you hit a coin with a spoon during an entire day.
I started by hitting my coin on its edge with a spoon. I used a small metal plate a found laying on the street as a rigid surface for the hitting. After about 2 hour of lots of hitting and almost no change I tried using a small hammer. It bended the coin faster but the results were a little deceiving. In the original site pictures, you see the inside of the coin bending uniformly outward., Instead I got flat edge and a smashed inside. After about two more hours of hitting I switch to a normal full-sized hammer.

I hit the coin until I got it to the right diameter (my estimation of my girlfriend’s finger diameter) and then I hit it with the spoon once again. The spoon flattens the edge surface making it smoother (which means less sanding and polishing afterwards). Also the spoon allows for fine control over the shape of the ring.

Once I got the edge to the right shape and diameter, I drilled a hole on the coin. I then used a screw to secure the coin to a drill and polished the outside of the rim by making it spin very fast. I used a fine sandpaper at first and some Brasso and a cloth afterwards.

Removing the inside of the coin was the most difficult part since I don’t have any clamp that can hold it without damaging it. Also, I could not preserve the outer part of the coin's inside as shown in the original site since mine was completely smashed. Anyways, in the end I removed the body of the coin usind some files and polished the inside of the newly born ring.

I gave the shiny (except for some dark spots caused by my inaccurate hitting) ring to my girlfriend who was very happy with it. I was happy to see it fitted her finger (although it was a bit loose).

Later, I discovered that the guy in the site used a silver coin (i know it is an obvious fact), which I suppose is easier to bend than my 94% steel coin.

Anyway, the end result is quite pleasing and nobody will believe you built a ring from a coin by hitting it with a spoon (unless you explain them how to proceed and show them pictures, people are very skeptical).

And yes I know, it is illegal to break money. This is why this never happened , you simply imagined visiting this site and seeing this project.

September 25, 2006

Wireless Skype Phone

At first, I saw on this site someone who modified his wireless phone in order to connect it to his computer, transforming it in a wireless speaker and microphone. I though it was kind of cruel to modify a working phone that way.

Some time later, my girlfriend gave me a broken wireless phone that belonged to her parents. I saw it was a nice phone so I tried to repair it but I couldn’t. Basically it worked fine, you can play with the menu, store phone numbers, dial, call, the sound quality is good, the reception is ok and the battery life is satisfactory. It has only one small problem: you can’t hang up. So unless you’re planning to call someone and talk to him indefinitely, it is kind of useless. So I decided to make it into a cordless internet phone.

General Idea

I wanted to have a wireless phone that connects to my computer speakers and microphone so I can use it as a PC wireless headset. Among other things, it coild be used to talk over Skype.

In order to achieve this goal, I hard wired the voice inputs and outputs of the wireless phone to my computer.
  • 1 cordless phone (mine is a VTech 2428)
  • 2 3.5mm plugs (headphone plugs)
  • 1 switch
  • 1 screw
  • 1 washer
  • some cables

Getting it done

First, I looked for the part of the phone circuit that manages the RF transmission. This was easy since the RF transmitter and the phone PCB are separated. The two parts are connected together with a grey cable ribbon which, at least in my case, is of very poor quality and broke very quickly. I replaced the ribbon with many pieces of individual wires. The result is much stronger and, most importantly, very colourful.

Having found the RF transmitter, I needed to discover which of its pins carries the sound signals to and from the wireless headset. So, I probed the pins of the RF transmitter in order to know which one is ground, which one carries the sound to the speaker and which one brings the sound from the microphone by using an old toy that generates a sort of music (you could use any sound generator but keep in mind you could fry it).

I figured the the ground pin had to be the top or the bottom one, since it makes sense to put the there (at least to me). To discover the speaker pin, I played a sound between two pins and tried to listen to it at the receiver until I hear it. For the microphone pin, I played a sound at the receiver's microphone and connected a speaker between two pins until I hared the sound.

Finally, I discovered that, for the VTech 2428 (and I presume for all the other VTech products that use the same transmitter) the first pin (top of the pin row in the picture) on the RF receiver is ground (which makes sense), the fourth is for the speaker and the last (bottom) is for the microphone.

Once the pins were discovered I simply soldered the 3.5mm plugs to them and secured the cables to the box using a big washer and a screw in order to ensure the connections wont break if the cables are pulled (don't worry for the space, this thing is mostly empty). By the way, I got my cables from a PC I found in the garbage so they were already color coded and labeled as “phone” and “mic”.

Also, I drilled a hole on the back of the case in order to get the cables out of the phone.

Since I don’t use the phone a lot, I installed a switch on it so I can turn it off. In order to interrupt the power flow into the device I desoldered the power connector, turned, the + leg up and soldered it back in so the + leg is not in contact with the PCB any longer. Then I soldered a switch between the leg and the PCB. I removed the phone line-out connector in order to fit the switch in its place. The line-in remains there and fully functional.

After putting it back together the phone was done and ready to use, It just needs to be plugged in to a computer. As a final remark, the sound quality is very good, both for incoming and outgoing signals. It can be used to talk on Skype from anywhere in the house, as a wireless spy microphone, or even to listen to mp3s while working on some new project (the later uses are not recommended).


Unfortunately, this hack doesn’t allow you to play the phone tones to the computer in order to dial or pick up Skype.

Future improvements:

I’m working on a ringer that will ring the phone when there is a Skype call. My idea is to use a square wave generated in the computer that will travel down the unused speaker channel(since the phone is mono) to switch on a ringer signal (90Vpp sine wave).

I would also like to add a pick up function but that seems difficult since I don’t want to use any other connection besides the ones already available.