Sorry for the lull. It has been a busy week with plenty of assignments and studying. Anyway, back to the point…
Spark Fun Electronics has announced a challenge to hack an image out of the 640×480 CMOS Camera Module they are offering for $19.95. The prize?
We will be offering a $200 in-store gift certificate to the first customer who can adequately document and report their successful single-image capture using this module.
Spark Fun Electronics has come through once again and is offering a color LCD 128×128 Nokia knock-off. If you ever wanted to do a project with a color LCD, it just got cheaper! Just remember that it’s a small mobile phone LCD and reliable at about arm’s length.
We’ve got the LCD and example C code for $20. You really can’t say no! We even sell the loose connector for $1 in case you are worried about soldering the tight 0.5mm pitch.
While reading lugnet recently, I stumbled upon an extremely interesting little robot. It’s creator says it best:
While waiting for the NXT system to come out, I decided to try my luck at making tiny robots… Often, when working, I would drop a SMT and have to take a magnifying glass to find it as it would get lost in the bits of filings, etc that were around the work area…
Believe it or not, this little guy is a sumo robot. When he senses he’s found, he runs full speed for the edge of the rink!
Several factors determine how dangerous electricity can be. Voltages, currents, resistances, and frequencies are the major factors that determine whether you will be hospitalized or just feel a little buzz. So consider all this the next time you plan on sticking your finger in an electrical outlet or straddling an electric fence.
Contrary to popular belief, you cannot feel high voltage directly and it will not kill you. Voltage is simply the amount of stored energy at a point in space. Current is the motion of that charge and can have lethal effects. As we will see later, there is a relationship between voltage and current that makes high voltage significant. This concept is best explained through the following analogy.
Similarly, voltage is of no danger unless your body completes a circuit (if you are touching the ground) and a charge is able to flow through your body.
There are several factors that influence current’s effect on your body. First of all, everyone has a unique chemistry so the effects are different for everyone. In fact, the small difference between a man’s body and a woman’s body cause significant variations. Secondly, the frequency of the current plays a critical role. The human body’s nervous system and muscles communicate using a frequency of 50-60hz making us extremely susceptible to current at this frequency. High frequencies and direct current are not as harmful.
The tabulated effects of current on the human body:
BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC
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Slight sensation Men = 1.0 mA 0.4 mA 7 mA
felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA
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Threshold of Men = 5.2 mA 1.1 mA 12 mA
perception Women = 3.5 mA 0.7 mA 8 mA
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Painful, but Men = 62 mA 9 mA 55 mA
voluntary muscle Women = 41 mA 6 mA 37 mA
control maintained
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Painful, unable Men = 76 mA 16 mA 75 mA
to let go of wires Women = 51 mA 10.5 mA 50 mA
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Severe pain, Men = 90 mA 23 mA 94 mA
difficulty Women = 60 mA 15 mA 63 mA
breathing
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Possible heart Men = 500 mA 100 mA
fibrillation Women = 500 mA 100 mA
after 3 seconds
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Ohm’s law, voltage = current * resistance, is the deadly relationship between current and voltage. Basically, if you connect a charged source to ground, the current through you is going to be directly proportional to the sources voltage. Therefore, a high voltage differential causes high current. The amount of current is indirectly dependent on your resistance.
Unfortunately, the human body makes a horrible resistor. Because we are composed mostly of water inside, the majority of our resistance is in our skin. Personally, my hand-to-hand resistance is about 540 k-ohm. Wetting down my fingers reduces my skins resistance and drops this number down to around 60 k-ohm. This is why you never want to be wet around electricity. Nine times more current is able to flow through my wet skin at the same voltage!
On simple property of electricity holds it ground in the example. Current prefers the path of least resistance. It would rather flow through the wire than the bird, which has a relatively high resistance compared to a power line. However, a charge always wants to obtain and equilibrium. If an object connects a charged line to a source with less charge (say the ground), then this becomes the easiest path for the source to discharge itself.
While I am writing, I should dispel another rumor. Most people assume an electric fence has current flowing from one end of the fence to the other when in fact it is charged uniformly from both ends. There is no significant current flow until you complete a circuit to the ground. In fact, the unit that powers an electric fence is sold as a ‘fence charger.’
This is a common misconception because common electric fences have a pulsating voltage. There is in fact a small current flow as the fence is charged and discharged, but the flow is not from one end of the fence to the other. It simply in and out of the fence.
Lately I have been daydreaming a lot in my laser communication course. Surfing around Google after class, I managed to find an article on sending serial port data over a laser link. The article is rather old (1997), but was published in a prominent Australian magazine. This is way back when a good, red laser pointer was only $70.
All said, this is an interesting read. It would be nice to see this applied to more practical situations. Many computers do not even have serial ports anymore. We have been discussing the feasibility of using a laser to send video signals in the DIY Live Forums. The idea is great because running cable your projector is often a major problem in home theaters. Unfortunately, I have no home theater and my only only monitor is an old, huge CRT. I will have to find another excuse to play with lasers.
On a side note, it is theoretically possible to send terabits of data per second over one channel, because the optical frequency of a laser is extremely high (~460 terahertz for a red laser). This bandwidth is limited to mere gigabits by the response time of current optical detectors and circuitry, though.
This is a Google Video of a 500kV switch opening in the Nevada desert. I really wish I could have been there.
Also check out a 345kV switch opening. This story got buried on digg. I’m not sure how something so popular got buried, but I saved something from the comments:
As the switch first swings open, the gap is very small and the voltage makes an arc as it breaks down the air (turning it from an insulator to a conductor.) Once this arc is established it grows in length as the switch is opened further since most of the air between the switch contacts has already been rendered conductive. Notice that the arc rises as time goes by because the arc heats the air and hot air goes up. The arc goes through the longer path because that hot air that is rising is still more conductive than the cold air down below which replaces it. Eventually the conductive air rises enough that the path through it has to also go through the colder non conductive air and this breaks the arc.
Spark Fun has barely had the capitol to invest in a hot-air rework station… as business has increased, revenue has allowed us to purchase a few bottom-dollar machines to help… it was all a waste of money…
If you have ever tried soldering ICs and surface mount elements to a circuit board, then you know how hard it is. Unfortunately, the only commercial alternatives cost thousands of dollars. At least until Spark Fun turned a $30 hot skillet into a reflow oven! “I don’t think anything can replace the large scale, multi-zone, IR/convection reflow ovens. But I could by 100 hot plates at $30 a piece”
They also review the traditional toaster ‘reflow’ oven and commercial alternatives. $30 is still outside my price range. I’ll take the soldering iron.