Measure Laser Wavelength with a CD and a Tape Measure

Obviously the wavelength of a laser can’t be measured with a scale as large as that of a carpenter’s tape measure. At least not directly and that’s where a Compact Disc comes in. [Styropyro] uses a CD as a diffraction grating which results in an optical pattern large enough to measure.

A diffraction grating splits a beam of light up into multiple beams whose position is determined by both the wavelength of the light and the properties of the grating. Since we don’t know the properties of the grating (the CD) to start, [Styropyro] uses a green laser as reference. This works for a couple of reasons; the green laser’s properties don’t change with heat and it’s wavelength is already known.

It’s all about the triangles. Well, really it’s all about the math and the math is all about the triangles. For those that don’t rock out on special characters [Styropyro] does a great job of not only explaining what each symbol stands for, but applying it (on camera in video below) to the control experiment. Measure the sides of the triangle, then use simple trigonometry to determine the slit distance of the CD. This was the one missing datum that he turns around and uses to measure and determine his unknown laser wavelength.

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Cutting a record… on a CD

Vinyl records are an amazingly simple technology, but surprisingly we haven’t seen many builds to capitalize on the ease of recording music onto a vinyl disk. [Seringson] made his own vinyl polycarbonate cutter to record his own records at home. The impressive thing is he did this with parts just lying around.

Just like the professional and obsolete record cutters of yore, [Seringson]’s build uses two speaker drivers mounted at a 45° angle to reproduce a stereo audio track. Each of these drivers reproduce the left and right audio track by carving them into the polycarbonate of a CD with an extremely sharp needle. From the video, the audio quality of [Seringson]’s record cutter is pretty good – more than enough to recreate the sound of a 1940’s 78 RPM record, but not quite up to the task of reproducing something produced and mastered recently.

We’re extremely impressed that [Seringson] was able to a record cutter out of scraps he had lying around. Now we’ll wait patiently until a combination record/CD is released.

Tip ‘o the billycock to [Gervais] for sending this one in.

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CD/DVD Polisher may save your backups someday

CD and DVD payers can often keep the music or movie going despite a small scratch. But occasionally you’ll have to skip to the next chapter/track or the player will just give up. But with data back-ups, a scratch can bork a whole set of files. We think that most of the time these headaches can be cured with this simple polisher.

[Wotboa’s] thrift store finds yielded almost all of the components needed to build the device. It’s made up of a couple of motors and a jig. One motor slowly rotates the upturned optical disc while the other spins the polishing pad. That pad is made from felt weather-stripping and is helped along with some plastic polishing compound. [Wotboa] asserts that five minutes in the noisy contraption will work wonders on any disc. You can get an idea of what it’s capable of by watching the video clip after the break.

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Freedom Toaster dispenses FOSS… for free

The Seneca College Linux Club figured out a fantastic way to help promote Linux to a wider audience. They took some surplus hardware and made an Open Source software vending machine. That is and isn’t a play on words. The project itself is an open source project, and the goal is to dispense other open source software in the form of CDs and DVDs.

Their build page shares all of the details. They acquired an older server cabinet which was on the way out from the IT department. It’s more than large enough to fit a person inside, which is overkill but it makes it much less likely that someone will try to walk off with the thing. Inside you’ll find a computer, two monitors (one is a touch screen for consumer use, the other is just an extra hidden inside for maintenance.

You must bring your own blank CD-R or DVD-R (but the burning is free). You can see the DVD shelf at waist-level on the fully painted kiosk above. The only thing we think is missing here is a USB port for brewing up a bootable USB stick.

[Thanks MS3FGX]

Automated CD ripper build from Lego and other parts

[Paul Rea] decided it was finally time to get rid his CD and DVD library by ripping the data onto a hard drive. He has a rather extensive collection of discs and didn’t relish the thought of ripping them one at a time. So he set to work building his own automatic CD ripper/duplicator.

Right off the bat he had several specifications for the build. He wanted it to be platform independent, reliable, and cheap to build. We think he really hit the mark, but he does mention that he’s got a second duplicator build in mind already. This version makes heavy use of Lego parts for the arm and gearing. The base has a stepper motor which swings the arm in an arc which reaches the input pile, the optical drive try, and the output bin. The arm itself has a two-part wooden gripper that is positioned over a CD and uses a limiting switch to sense when the vertical orientation is at the proper point for gripping a disc. We enjoyed reading his log as he discusses the various building challenges he encountered and how each was overcome.

We’ve seen a few other builds like this before. One of our favorites is from way back.

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Make Your Own Odometer from Scraps

For those out there who would enjoy a quick and interesting weekend project, this odometer made by [PeckLauros] is for you. Featured on Instructables it is made from the simplest of materials including some cardboard, a calculator, wires, glue, hot glue, magnetic drive key, an old CD and a reader, and a rubber band.  The magnets, when attached to the CD work in a calculation to add 0.11m to the calculator when a magnet closes the circuit. [PeckLauros] points out that since it is a homebrewed device, it does have flaws such as adding 0.11m twice when the CD is rotated too slowly.  It is easily fixed by simply running faster.  The video is below the break.

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Build a simple switch

Forget hacking an easy button, grab a couple of those outdated CD-Rs and build your own switch for that next project. This was developed with handicapped accessibility in mind; assembled easily with common products and it’s fairly robust. In fact, our junk box has everything you need except the adhesive backed copper foil. Combine two old CD’s, covered in copper on facing sides, separated by two strips of Velcro to separate the conductors. When pressure is applied, one CD flexes to make contact with the other and complete the circuit. So easy, yet we never thought of it. We’ll add it to our list of homebrew input devices.

[Thanks Michael]