Subject:
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Re: digital camera entirely made of mindstorms?
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 27 Sep 2000 03:19:09 GMT
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Original-From:
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Steve Baker <SJBAKER1@AIRMAILavoidspam.NET>
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Reply-To:
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sjbaker1@airmail.#SayNoToSpam#net
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Viewed:
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963 times
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Amnon Silverstein wrote:
>
> This thread is pretty old, but if any of you have questions about how I made
> my pure-lego digital camera, I would be happy to answer them.
>
> The camera scanned the sensor by tilting the sensor. It used the magnifying
> glass from the Adventurer's set. It took a 40 X 40 pixel image, one pixel at a
> time. I always stepped the motors in the same direction, to reduce any gear
> lash problems. I took several scans and averaged the results to get my best
> readings.
(This may be marginally off-topic - but someone will find it useful)
That reminds me of the digital camera I made 'by hand' about 15 years ago
by *carefully* milling the 'lid' off an old DRAM chip and replacing it with
a microscope slide cover. DRAM chips need a pulsed 'refresh' signal to prevent
them from losing their data - and if that signal is absent, the '1' bits decay
to '0's in a fairly short amount of time (actually, I think it was '0' bits that
decayed to '1's - but whatever).
The key thing that lets you turn it into a camera is that the DRAM decay time
is influenced by the amount of light falling on the RAM chip!
Hence, if you fill the RAM with '1' bits, then stop the refresh signal for
some amount of time, then turn it back on again, you capture an image in the
RAM chip's memory. The amount of time you leave the refresh off for controls
the 'shutter time'.
The result is only a binary image (light or no light) - but by taking many
images with varying 'shutter times' you can get a greyscale of sorts.
It takes quite a bit of messing around to get the right mapping of RAM bits
to physical location on the RAM chip's surface - they aren't laid out as
logically as you might expect. There are also areas in the center of the
die where there are no RAM cells (power and addressing logic
runs between large blocks of the actual bits).
Still, it worked VERY well. With enough time to take exposures of varying
lengths, you could get images with very high brightness ranges. If you
only want to detect light and dark, then a single exposure will suffice
and you can detect quite rapid motion.
I have no idea whether this would still work with modern DRAM chips though.
This was done in the days when a 16kbyte RAM was a LOT.
Anyway, if you could make it work, it would be an extremely compact, lightweight
and power-efficient camera for a robot....and if you could get good at milling
the tops off without damaging the silicon wafer, they'd be pretty cheap compared
to a large CCD array.
I built mine into a small computer board that was going to go into a
radio controlled model plane. The idea was to have the computer try to
recognise the horizon line and automatically level the wings of the plane
when you pressed a button on the radio. That part didn't work - but it
*was* small enough, light enough and low enough in power consumption - which
wasn't bad for early 1980's technology!
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message has 1 Reply:
 | | Re: digital camera entirely made of mindstorms?
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| Oh! I remember a story about that in one of the Apple ][ magazines, or Circuit Cellar or something. They took a picture of a lightbulb I think (I guess their version needed more light than yours). They used the same technique you describe. I thought (...) (24 years ago, 27-Sep-00, to lugnet.robotics)
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Message is in Reply To:
| | Re: digital camera entirely made of mindstorms?
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| This thread is pretty old, but if any of you have questions about how I made my pure-lego digital camera, I would be happy to answer them. The camera scanned the sensor by tilting the sensor. It used the magnifying glass from the Adventurer's set. (...) (24 years ago, 26-Sep-00, to lugnet.robotics)
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