Hackaday Links: March 20, 2011

SNES Arcade Cabinet


[Daniel] let us know that he finished up a SNES arcade cabinet he has been working on for awhile. It looks so good, he says that his wife has even agreed to let him keep it in the house!

DIY Overhead projector beamer


[Liquider] sent us some information about a DIY beamer he built using an overhead projector and an old LCD panel. It looks like a great way to get a big-screen wall display set up in no time.

WordClock gets a makeover


[Doug] wrote in to share with us some progress he has made on his WordClock. You might remember our coverage of this creative timepiece a little while back. This time around, he has built a new control board, and is using vinyl stencils for a much cleaner look.

Interactive water fountain


[Gerry Chu] is well known for his water-based imagery and projects. His most recent project is a water fountain that interacts with passers by. There are no real build details as of yet, but we hope to see some soon.

Sixty Symbols explains why glass is transparent


Do you think you know why glass is transparent, but a brick is not? If you looked it up via Google, you are likely mistaken. A professor from the University of Nottingham explains why the Internet is so, so wrong about this, as well as how energy gap determines if photons of light can make it through a piece of glass. [via i09]

21 thoughts on “Hackaday Links: March 20, 2011

  1. Regarding the University of Nottingham video: as far as completely explaining why glass is transparent, it leaves a little to be desired. One might envision from the explanation that any photon with more energy (shorter wavelength) than the visible spectrum will pass through glass and any photon with less energy (longer wavelength) would be blocked. But radio waves can pass through glass (and I also believe UV is partially blocked). Why is this?

    Well, it is not just about exciting electrons to a higher energy state. There are other ways to impart energy to an atom, e.g., vibrating it, rotating it, ionizing it, etc. For glass, visible light happens to fall in between the light which causes vibration (IR) and the light which causes excitation (UV), and since visible photons are too energetic to cause rotations, but not energetic enough to cause excitations (as described in the video) they fail to be absorbed.

  2. Regarding the University of Nottingham video: I agree with Insipid M. The explanation regarding the photon energy is a little too simplistic. Isn’t there a lot more to it? (adsorption, reflection, refraction, re-emission, multiple energy level changes, etc.)

    I think an additional explanation about why light gets dimmer as the thickness of the material increases is also warranted. Leaving that out implies thickness wouldn’t matter.

  3. Sure the vid leaves something to be desired if you’re getting you’re degree in materials engineering or physics, but it was recorded with a target audience for you’re average Joey Bloggs walking down the street.

  4. Having physics degree in optics, I too agree that the light video is over simplified. We just jumped to quantum wave equations and did not play around in the electron ball pit. Throw in a few more integrals, some vector calculus, and Maxwell, and then we’ll be on our way.

    For example, Germanium lenses are transparent in the infrared, but not in the visible. Hum… the visible has higher energy photons than the IR. Shouldn’t they be transparent Doc?

  5. @Joe: Isnt that exactly what the video explained? Infra-red has low energy, so it cant put the ball on the shelf, so continues on its way to the other end of the room.

    I quite liked the video as I had always wondered why glass is transparent. I know its a simplification, but now knowing that it’s to do with energy levels, and knowing stuff about energy levels, i can infer a lot of other things.

  6. There is a problem with the beamer, the heat from the bulb in the projector will burn the LCD causing a ‘bad spot’. I fixed the problem on mine by raising it up a little and ducting airflow from a little fan.

  7. @Brian.Holiday did you even read the article? “After installing all the driverboard and powersource i had to build a cooling system in order to prevent the screen from getting damaged through the OH’s lightsource.

    Cool air gets sucked in at the front and flows under the screen right through the driver board.”

  8. @dmo: Surely the reason for glass becoming more and more opaque with thickness is just due to impurities. The light may go through glass, but if there are a few atoms of some element in it, it will cause a slight amount of light reflection. For a piece of glass a few millimetres thick you’d never notice, but as it gets thicker, the chance of meeting an impurity increases and it gets more and more opaque.


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