Feb 16, 2013

The laser-equipped Lego train

In a previous post I was not very happy with the results of my opto-acoustic capture of the miniature gramophone record, so today I thought I'd try to illuminate the record surface more evenly.

Of course, the straightforward solution is to build a circular LEGO® railroad track around the record and have a laser-hauled train run around the track, illuminating the record surface with coherent light at a constant tangential angle, while a camera captures the image at long exposure.

This time I didn't want to go through the trouble of positioning the high-resolution camera and only got this:

I learned that Lego is not very good for laser work in general; specifically the trains don't run very smoothly, as you can see in the above pic. Updates with audio will follow, anyway. In the meantime, here's a video.

Bonus points if you can hear what's happening in the background.

Update: I didn't post an audio update, because the audio was useless. And the whole laser thing was a dead end anyway. Instead, I edited the high-res photo I took earlier, removing the extreme shadows using Gimp's Dodge/Burn tool, then changed my Perl code a bit so that it actually stays on track, and made this:

Now I can put the robot back together and close this case.

12 comments:

  1. Perhaps try a line laser (e.g. https://www.adafruit.com/products/1057) rather than a spot laser so it's not to sensitive to the rocking motions.

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    1. Hey thanks for the link, looks very useful :) I used to have a linearly dispersing laser lens but I've lost it.

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    2. You could still mask the pointer with some layers of electrical tape. I have no idea if it would improve your readings at all. :-)

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    3. : ) It seems to attenuate my sub-milliwatt laser too much.

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    4. if you have a lazy susan or at least can grab a lazy susan bearing, placing the record on a stand in the middle and affixing a larger surface with a cutout in the middle (for the stand affixed to the base to poke through the middle of the bearing) should provide a more stable method for rotating the laser while keeping the record stable. Small lazy susan bearings can be had for under $3 a simple friction drive system should allow you take an electric motor affix a cylindrical object to it and affix the motor to the base so that the 'wheel' touches the top section while avoiding the base thus rotating the pointer at a constant speed. In theory this should give you more reliable results.

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  2. isn't that Minecraft running in the background?

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  3. Have you considered a flatbed scanner instead of the camera?

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  4. Hey Oona,

    very cool project! I'm wondering: is the Perl code you wrote to process the image and generate the audio available somewhere? I'm always in to learn some new Perl tricks, you never know when they might come in handy.

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    1. Unfortunately not, I don't like publishing random Perl hacks.

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  5. Ekana tulee mieleen että voisi kuvat tuon kyseisen levyn raskaamman sarjan kameralla, esim. Canonin järkkärillä niin että useasta suuren polttovälin kuvasta saadaan kasaan valtava kuva ja samalla saadaan käyttäen pientä ISO arvoa minimoitua häiriö kuvassa ja valaisuun kun käyttää esim. 10W valkoista lediä niin luulisi saavan paremmin esiin detailia levystä.

    The first thing that comes to mind is to use a very high resolution low noise camera (Canon DSLR for ex.) to take multiple pictures in a grid using a telephoto lens and stitch those together in a similar way that of the gigapixel project.

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