Reduce, reuse, recycle.
It’s a mantra for the new millenium, for some people quite literally. Computers are routinely recycled these days, yet reducing and reusing are by far the more important components of this triplet. In this column we’ll look at an innovative re-use for old computer hard drives.
This gadget uses two hacked hard drives to draw Lissajous figures using a laser. The voice coil, which is normally used to position the head assembly on the platter, is hijacked to instead move a hinged mirror. With two hard drives, two voice coils, and two hinged mirrors, you can displace the laser beam in both the X and Y dimensions.
The software for this particular gadget is called Pure Data, and is an extensible dataflow programming language for audio and video processing. It’s an interesting item in itself that may appear in a future column. In this project Pure Data analyzes the user’s voice to extract the dominant frequencies. These frequencies are then used to drive the X and Y positioning mirrors, creating a Lissajous figure that represents the voice of the user.
Pure Data generates the line level signals, and a 30 Watt stereo amplifier drives the voice coil, with one stereo channel controlling the X displacement and the other controlling the Y.
The WWW page for this gadget is short on construction details, but references what seems to be the original hacked hard drive laser page, the hard drive laser scope, which has lots of good information.
Improvements?
This project could be improved by using front surface mirrors. As the name implies these mirrors reflect from their front surface, rather than the rear like a typical painted glass mirror. Every time the laser passes through the glass of a typical mirror there are additional reflections that distort the laser beam.
A twist on this project would be to reuse the platter motor as well by mounting a multi-sided rotating mirror on it and using it to provide one dimension of displacement and using the voice coil to provide the other. With a microcontroller that is synchronized to the rotating mirror modulating the laser it should be possible to render rasterized graphics. If you build such a thing be sure to let me know so it can be featured here in Gadget Freak
Steve Ravet
EDN Gadget Freak
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