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.