persistence of vision led text display (and my failure to find it)
Fred Hawkins
Posts: 997
Msng n Lbry, among my stacks and stacks of Circuit Cellars and Dr Dobbs (before it was Borged), is an article about using a vertical string of leds to spell out messages or simple logos.
Importantly, the gimmick was that the string didn't move; if you looked at it directly it would mean nothing.· But as you looked around, your peripheral vision and rapid eye movement would spread out the flashes, leaving a message. Bi-symetrical logos was optimum because you never·'saw' something backwardly.
I like the idea and see it as a·natural for the prop to handle. But I would sure like to find that original article. As I recall the article, the writer's main tech-problem-to-be-solved was getting a big enough eeprom to store his messages.
Alas, I've googled until I'm black and blue, and never quite seem to find it. I've even spent whole afternoons looking through Circuit Cellar's search results. All to no avail.
So I ask this·high-skill resource, aka the prop forum: do you know where this article or a close facsimile is?
·
Importantly, the gimmick was that the string didn't move; if you looked at it directly it would mean nothing.· But as you looked around, your peripheral vision and rapid eye movement would spread out the flashes, leaving a message. Bi-symetrical logos was optimum because you never·'saw' something backwardly.
I like the idea and see it as a·natural for the prop to handle. But I would sure like to find that original article. As I recall the article, the writer's main tech-problem-to-be-solved was getting a big enough eeprom to store his messages.
Alas, I've googled until I'm black and blue, and never quite seem to find it. I've even spent whole afternoons looking through Circuit Cellar's search results. All to no avail.
So I ask this·high-skill resource, aka the prop forum: do you know where this article or a close facsimile is?
·
Comments
A simple routine would read a character from the display buffer, look it up in the font table and then output a column at a time with a delay between each column before moving on to the next character.
*Peter*
Look about midway down on this link...
http://forums.parallax.com/showthread.php?p=574524
...there, posted by Dave Scanlan·is a POV demo that I wrote early on when the Propeller was first released.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
It is interesting you bring this up, because I have recently been thinking about doing the same thing [noparse]:)[/noparse]
Many years ago I saw a 'professional' installation of this type of display at the Boston Museum of Science.· It was a vertical box about 3 ft high mounted across the room and appeared as a simple line of light when viewed head on, but an image was able to be seen in the corner of your eye as you turned your head.· Very cool.
It seems to me that this type of application must be very similar, if not identical to other pov applications - even if they are moving.·But perhaps there is some specific timing that makes all the difference for a stationary display to be effective.
Post Edited (Agent420) : 5/12/2008 12:20:07 PM GMT
So early 90's, eh? That means downstairs and diving into the boxes. Seems just like yesterday to me.
And an apparent double mailing of an issue during a resubscription, remarkable because it has an article by one Chuck McManis. Something about a little car. I'd be more specific but now I can't find that article either.
Newbie alert: if you want some interesting challenges, get a cd of back issues from circuitcellar.com. The cd's are all worthwhile, and implementing many of the projects ought be fun to with a propeller, and probably simpler than the original solution.
And yes, CC is probably the best periodical dedicated towards embedded circuit design and related electronics.· An excellent investment imo.
·
In March 2003 the ad went back to a compass, a breadboard, a prototype board, an LED terminal (4 digit alphanumeric), Stamp Modem, a audio amp and a sound module w/ a speaker. Prices range from $29. to $89.
Post Edited (Fred Hawkins) : 5/16/2008 3:00:46 PM GMT
http://sub-zero.mit.edu/fbyte/ledart/obelisk2/
I hope to make it to a Burning Man one day...
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Searider
Graham
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Here's the CC article 'Lightstick II' from Feb '94, attached below.·The strobe timing seems to default to 466us to begin with, with the option to increase or decrease it on the fly.· The article doesn't discuss much of the technical aspects of pov parameters, but seems based on a previous project named 'Lightstick" by artist Bill Bell...· I believe Mr. Bell's display was the one I saw at the Boston Museum of Science.· A Google returns several results on Bell's Lightsick.· I'm sure more detailed information may be obtained on one of those sites - he seems to be a pov guru [noparse]:)[/noparse]
http://www.google.com/search?hl=en&q=bill+bell+lightstick
Some other good technical information seems to be in Bell's original patent #4470044.· I've not had time to fully digest all of this, but these stationary displays are somewhat unique in that they are based on involuntary 'saccadic' eye movements we make all the time.· No doubt it is the synchronizing to this timing that is important.
http://www.freepatentsonline.com/4470044.html
Post Edited (Agent420) : 5/19/2008 1:06:37 PM GMT
I was surprised when you said it was from the 90's, and really stunned when it turns out to be the early 90's (and back when CC was still saddle stapled).· It was really just a little while ago -- one or two years, maybe four years ago... Does this mean I am old now?
So, found the issue and reading it now.
·
edit -
I've attached the patent (in pdf format) below for those that don't wish to go through the Freepatent's registration....· It's easier to read and includes diagrams.
Post Edited (Agent420) : 5/19/2008 5:12:38 PM GMT
Sorry for the late response... I am an expert on this... No-one understands rapid eye movements. All of the texts are wrong. To get a reliable POV for everyone you need to implement it in the standard way. This kind of device would work for most of the people most of the time... but not for all of the people all of the time.
This kind of device would be very interesting for visual scientists, who would like to quantify and study various pathologic eye movement disorders (genetics, progression etc) It would also make a dandy screening device.
Build it and they will come.
Rich
I think that's this item's charm -- it remains enigmatic until you 'get' it.·My current·plan·is to use·a·two extra offset LEDs·that momentarily·flash to attract attention, and feed the data pdq to the column.·Here's a thought:·have the attractors blink in a simple pattern that·'trains' the eye to make the movement, then spring the·trap.
I do like this detail from Bell's patent: "Researchers ...·have·made measurements of the angular rate of saccadic eye movement and found the angular rate to be uniform from person to person, and largely not consciously controllable. Angular rates reach a peak at the middle of the saccadic movement, and may be about 220-250 degrees per second for movements of 5° in angle and about 450-500 degrees per second for movements of 20° in angle."
So one expects a working solution depends on the·environment. Something installed·on a street corner would be different·than a breadboard·on ·a workbench.
Fred.
My dentist has auto-stereo prints hanging on his wall... the idea is to cross your eyes and the 3D comes out after a while. I think there is a huge commercial potential for anything that looks interesting and distracts a person's attention for a few minutes.
That's what I love about this forum... just about everything gets discussed.
nice thread.
Rich
Rookie Alert: Plus I don't get how the data is put into the 595's. Unless 'cascading' means a bucket brigade brute force·bit by bit shoving down the line.... All in all, it doesn't look like the i2c bus that the propeller environment has taught me to know and love.
So I poked around TI and turned up this nerdy 'fun lights' pdf: http://focus.ti.com/lit/an/scpa043/scpa043.pdf·which uses their TCA6507 7 led controller. http://focus.ti.com/docs/prod/folders/print/tca6507.html
TI also has a PCF8875C which seems to be saying that it can handle 16 leds. http://focus.ti.com/docs/prod/folders/print/pcf8575c.html
It doesn't seem to have the same bells and whistles as the 6507 but maybe the 8875's·presentation is not dumbed down as far as the 6507's.
·Yes, the 595's are fed one long continuous bit stream. The serial data flows through each 595 via the Ser(14) and OH(9) pins.·No changes take place at the 595 outputs until the Strobe signal is sent.· So you could have virtually any number of cascaded 595's, you just have to spit out 8 bits for each one, and then end it with the Strobe to trigger all the outputs simultaneously.· The 1st 8 bits out would be for the last 595 in the cascade, and the last 8bits out would be for the 1st chip in the cascade.
This serial method really bears no comparison to I2C.· It's not any std 'protocol', it's just a bit banged interface.· You have to create the logic and io programmatically.· Really, a simple repeat loop would do it.
This idelology is not far removed from my original Hello World led matrix project... take a peek at that code for an idea.· Specifically, the repeat idx loop takes 16bit word data and outputs it 1 bit at a time while also cycling the clock pin.· If you expand that idea to accommodate even longer bit lengths (or, alternatively viewed, groups of bytes) you have the foundation for dealing with cascaded 595's.
http://forums.parallax.com/showthread.php?p=725126
I'm sure there are a couple of newer chips like those you found, but really the 595 is cheap, easily located, available in friendly pdip form·and handles some good current (important for strobed led applications), so I wouldn't dismiss it so quickly.·· Also, in this application I think it is important to be able to strobe all the led's at the same time, something that might be difficult to do if you use·other controller chips on an i2c or spi bus.
Post Edited (Agent420) : 5/28/2008 1:17:36 PM GMT
flashy beepy: YouTube is jam packed with LED POV stuff. This one, a·globe made from 256 smd white and 36 red LEDs,·is very cool: http://www.youtube.com/watch?v=oLygWkHo9nw
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