March 14, 2011

toothpaste diode

One day I was reading the back of a toothpaste tube and realized that the secant ingredient was Hydrated silica which is nothing more then silicon oxide mixed with water. So I started to wounder if I making a from it transistor would be a possibility. I thought it might be easier to start with something simpler. So I decided I'd make a diode. The detailed of why this worked is after the photos. If you just want to see the photos and don't care about the chemical proses involved then all you need to know is I smeared toothpaste on a peace of chrome and lit it on fire with a propane torch. After testing I found that I had to add a 10 k resistor in series with the diode because the breakdown voltage was so low that my multimeter  was braking it down. The diode layer is thin and can be scratched off easily resulting in a fun hunt for a new diode spot. I did this once and it took half an hour to find another spot that worked as well as the first one. This diode is probably only useful for crystal radios as anything else would have to much voltage. 

Its showing 0 conductivity the line on the meeter
just extends past that point. 

Here you can see the 10 k ohm reading from the resistor the
 diode itself had almost no readable resistance. 
My toothpaste contained  13 ingredients:
Water, Hydrated Silica, Glycerin, sorbital, PVM,MA copolymer,
 flavor, sodium lauryl sulfate, cellulose gum, sodium hydroxide,
 propylene glycol, carrageenan, sodium saccharin, dye, and fluoride. 
If I lit this on fire then most of it would burn off leaving me with mostly silica and sodium covered in ash.

So it was pointed out that when bonded sodium looses its outer electron and thus will become a p-type semiconductor. So this explanation is now all BS. Anybody know whats making th n-type semiconductor?

Hear's the scientific bit that makes it work:
Sodium is negatively charged so if I debond it with heat it will stick in the Silicon giving me an n-type semiconductor. Witch is half of a diode. I'm not positive but I now think that it is the Sodium Iauryl Sulfate steeling electrons from the shakedown of other chemicals and becoming negatively charged that is forming the n-type semiconductor. To form the other half I needed a P-type semiconductor so I looked around my desk and found a peace of chrome.(the chrome might not be necessary as the Sodium might make the P-type semiconductor) Chrome is positivity charged so if I got some of it to mix with the Silicon then I would get my P-type semiconductor.  Luckily for me the toothpaste contained Sodium Hydroxide AKA Lye. Lye reacts with chrome and is often used as a dechromeing agent. As it oxidizes the chrome it creates heat witch burns off the lye. Now there is a thin layer of chrome doped silicon under a layer of sodium doped silicon all rapped up under a layer of soot  which can easily be cleaned off. After cleaning you are left with a peace of metal with a thin layer of silicon on it with spots that work as a diode, spots that are non conductive, and spots that are always conductive. 

Note: I'm not a chemist nor do I necessarily know what i'm talking about if you know I'm wrong let me know and I'll consider revising this. 

March 4, 2011

Bristle Bot

      Bristle Bots are a simple device that translate the vibrating motion of a pager motor into foreword momentum. As the motor vibrates its kinetic energy first pushes the bot down and then pulls it up. As the bot is pushed down the bristles work like a spring compressing. Then as the vibrations pick up on the brush the bristles decompress if your brush has most of the bristles angled in one direction this pushes the bot in the opposite direction.
      I started looking into steering these devices and found that by shifting weight over the device you can change its center of gravity and make it tern. The problem with this steering system is that it requires a fairly wide platform. The bots that use this principle are made with two bristle pontoons with the vibrator and weight  in the middle. This seemed to  make it hard to scale down the steerable bots. Because most of the fun of these bots is there size i wanted a design that I could scale to any size so I started trying different steering methods. This is the result.

 I wanted my bot to only have one brush so I decided 
to force the bristles into changing angles to steer the bot.
Sending current into the motor causes one paddle
to compress the bristles and the other one to pull away
from them. Switching the polarity reverses the paddles.

I removed the inner bristles from the steering
section because it increased the sensitivity of the handling.

The Bristle bot steers comparably to other bots I've seen online. I don't have a video camera to show it to you it in action.

December 9, 2010

Retinning soldering iron tips

I use cheep 30w Radio Shack soldering irons. They work reasonably well for most soldering. The only problem is that their tips are junk. They don't stay tinned properly and before you know it only half of your tip is tinned. I'm in a perpetual state of broke so i didn't want to wast my money on a new tips for my irons. I just used them until there was almost no tinning left on them and I had to hold it at just the right angle to solder anything. 
Before retinning
I know that an iron could be retinned with tinning junk you can buy but that cost the same as the price of the tips i didn't want to buy. Besides I figured that I could tin it with normal solder if I cleaned the tip first. The ends of these irons where so caked with baked on junk that they where going to need some serous cleaning. They where also pitted in spots so I thought I could solve that problem at the same time. I chucked them in my drill and filed the old tinning and junk off the tips with a nail file. Next I reshaped them with a mettle file. This left them ruff and dull looking so I used steel wool and the drill at top speed to smooth the tips out until they where a shiny. Now the tips just needed to be tinned now so I reinstalled them into the irons and plugged them in. The copper surface of the iron worked better for transferring heat then the tinned surface so they heated up almost instantly. All I had to do to finish the project was completely cover the end of the iron in solder and wipe of the extra solder on a damp paper towel. Now the tips are better formed then they where new and the tinning is as good as new. 

After retinning. Its not the best pic my camera doesn't take micro photos well. 

December 8, 2010

Replacing Capacitors in a Motherboard.

     Last year I was given two computers. One of them worked fine but the other one started POST then splashed an error code and shut off. The code showed up and POST hit the kill switch almost simultaneously. It took an hour of restarting my computer righting down three of four digest and starting the computer again to get the entire code. After Googleing the error code I found a website that vaguely pointed to bad capacitors. After a closer inspection of my motherboard I confirmed that the caps where bulging. Scavenging through my junk box I discovered that I had every kind of capacitor possibly imagined except the 2500 pf  caps to replace the bad ones on the motherboard. I also have heard all kinds of stories about needing all kinds of specialized junk to work on motherboards like temp controlled soldering irons. all i had was the 20 year old 30 watt trash shack tinder box I annexed from my dads electrical box the year before. I wasn't letting any details like them stop me. So i rummaged through my box of junk some more and found another motherboard with 6000 pf caps. If I placed two of them in series i would end up with 3000 pf caps. Close to the 2500 pf i was looking for. There was also a 15 % tolerance to work in so i did some more math.
2500 + 15% = 2875
 (6000/2) - 15% = 2550 (Now that i think of it this should have bean 30% tolerance as the two tolerances would add together.)
After I finished the math I mumbled something about how close enough was good enough and decided to go on with the project.
I decided to take the caps of the donor bored first. I think thy must have used some kind of conductive glue instead of solder because it wasn't melting. I spent what seamed like hours bent over to board trying to get the solder to melt but it just sat there laughing in my face. I cracked after that hour and went for the heavy machinery; my rotary tool with a cut off wheel. I'm almost positive I was laughing maniacally as i slowly lowered the wheel to the board intent on cutting out the offending parts. It was probably because of this laughter that I inhaled all the dust from the Dremel in one big gulp causing me to have a coughing fit. Old motherboard 3 me zip (the third offence of the motherboard is a deferent story). I was about to through that cursed motherboard away in disgust at being thwarted once more by a peace of fiberglass. When the realization hit me that I could cut it too peaces with a pair of tin snips. Finally I would have my revenge on that board. It also got the capacitors off it to so it was win win i suppose. I ended up leaving the board on the bottom of the caps and just soldering wires onto the tag end of the lead that was still sticking out. Linking pairs of them together in series first.* Then I soldered leads onto the remaining tag ends to install into the board. Next I had to desolder the caps from the board I was working on. I was apprehensive at first because of my past experience with this posses but as I placed my iron on the first lead the solder melted almost before the iron hit it. all I had to do was push in the leads with the iron and the bad caps fell out. This was a huge relief i thought i was going to have to pull all the capacitors off the board by hand and solder to the exposed leads left behind.
 So I reassembled the computer and installed terned it on. It booted up on the first try. I later discovered that the on board Ethernet cart and sound card didn't work. So i added expansion cards for them. The computer worked for me for about a year before I no longer needed it and took it apart for other projects.

I do not recommend that you try repairing motherboards yourself it's a pain. This is simply to show how I solved a problem not to show you how you can do the same thing. I also don't recommend playing with electrolytic capacitors without knowing what your doing I've seen them blow up and it can be scary. I also never would have done this if I didn't have another computer to use as I might have killed the computer and all its parts.

*(Electrolytic  capacitors are linear so you have to use the right orientation or they will blow up.)