Description of FrostByte's Obelisk POV displays needed

SpokePOV kit for bikes

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MooMisterCow
 
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Description of FrostByte's Obelisk POV displays needed

Post by MooMisterCow »

Hi again,

I posted a while back about potentially using a spokePOV as a static "SignLine" display. A few weeks later and I've learnt enough about electronics to build my own POV display from scratch.

However, so far the results of having a static display (admittedly only 7 LEDs so far) and glancing quickly from side-to-side, are not as amazing as I'd hoped. Perhaps I need a whole lot more LEDs. I'm planning on about 200 white LEDs, hopefully with PWM so I can display a grey-scale image. Or perhaps it's an issue of frequency (although altering frequency merely seems to scale the X axis of the display).

However, I have third-party evidence and even photos of such a device (Obelisk 1 and 2, built by FrostByte) that look pretty amazing.

http://mayhem-chaos.net/photoblog/images/mona_lisa.jpg

So, to give me continued hope for my own project, please can someone tell me just how amazing these things are in person and that I'm not wasting a lot of time and money on a futile and doomed experiment!!! :roll:

[Apologies for posting here when not actually purchasing a spokePOV, but the spokePOV ultimately didn't fit the bill, and there aren't too many forums on the web dedicated to POV displays!]

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foobert
 
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Post by foobert »


adafruit
 
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Post by adafruit »

fbyte's obelisks were pic18's running at 40mhz to allow for ultra-high frequency PWM. each 'pixel' was made of 4 leds (red, orange, green, blue) with one LED per microcontroller line. it was incredibly expensive (i think around $10K) and all done in assembly.

MooMisterCow
 
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Post by MooMisterCow »

Hi all,

Feeling a lot more positive than when I wrote that last post. I've upped the LED count on my test rig to 21, and it seems that the following are factors in whether or not you can see the image clearly:-

1) It's got to be dark. Unlike the moving "spacewriter" POVs, the more background interference there is, the harder it is for your eye to see the POV image. The blurb for the SignLine commercial POV display ($1000!) says you can easily see the image in daylight. I'm not so sure.

2) A greater Y resolution means you can see a greater X resolution. I guess there is an upper limit, but as I add LEDs (Y), I can make the picture wider (X) and still see it, and the increased resolution helps the eye to make the image out.

3) More iconic images are easier to see. For example, I had a 21x21 pixel smiley face image, and initially I messed up the bin->hex conversion so it came out wrong: my brain couldn't make out the image at all. But when I fixed the data, the smiley face was very easy to make out. I guess there's some crazy subconcious processing going on.


Thanks for your comments about the Obelisk. The progress I've made makes me less likely to think that it was all some expensive joke, and that it actually did work in reality. The PWM version must have been pretty amazing to allow you to recall an image of the Mona Lisa scanned column by intricately colourful column into your brain.

Regarding the cost - I guess the expense comes from the LED count. I'm tempted constantly to use RGB LEDs, till I remember that each one will take three lines to drive it, and that'll probably mean more microcontrollers, more boards, more power...

Still, when you can buy 20 for $12 (http://www.ledshoppe.com/Product/led/LE1011.htm) it's pretty tempting.

Perhaps verison 2.0...

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foobert
 
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Post by foobert »

just out of curiosity... at what frequency are you flashing your leds and how fast must you move your head?

i have two applications for this. a wrist watch. and a display viewable by moving traffic. for the latter i was thinking of using the at90usbkey. lots of io, bootloader over usb, onboard flash memory for message storage, usb host so you could attach a keyboard and change the method in real time. a truly tantalizing little device ecept for the damned 50 mil headers.

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Post by MooMisterCow »

Currently the prototype is running at 800Hz.
The hardware is an ATmega32 running at 16Mhz.

The wetware aspect involves an algorithm of look a few feet to the left of the display, then glance to the same distance to the right, and repeat. You don't need to shake your head. In fact, if you do then you tend to end up feeling dizzy and even then you have to drop the frequency because you can't shake as fast as you can move your eyes. :shock:

Your wrist watch idea would probably end up annoying (unless you design it to be swiped like a Spacewriter), and as I said, the effect is better with very low light levels.

The traffic display aspect would work. The only thing to consider is that you cannot control which way people will look across the device, so your image may come out reversed. I'm thinking of text in particular. However I've noticed that images that make sense jump out at you, whereas others are not so obvious. So you might find that people automatically learn to read the correct left to right orientation. But I wonder whether having images jump out of nowhere at you while driving at 80mph might cause issues. :D

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foobert
 
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Post by foobert »

call me evil but, issues, that's the point. i was hoping for something accidentally, (unfortunate word, that), readable at, say, 20 mph. just hang it on the side of the house and have it pop up in folks' peipheral vision as they roll on by. all the better if 95% of them don't see it. the other 5% can seek counseling.

and i still like the watch. the problem would be making it readable at just a foot away. might have to read the reflection in a window or mirror.

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Post by MooMisterCow »

I like the idea of an "evil drive-by blipvert" even more!

The watch might work if you had some really small LEDs. 5mm ones would make for a pretty chunky watch. Then again, why have a watch when you can sew the LEDs into the sleeve of your jacket?

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Post by adafruit »

MooMisterCow wrote: Regarding the cost - I guess the expense comes from the LED count. I'm tempted constantly to use RGB LEDs, till I remember that each one will take three lines to drive it, and that'll probably mean more microcontrollers, more boards, more power...

Still, when you can buy 20 for $12 (http://www.ledshoppe.com/Product/led/LE1011.htm) it's pretty tempting.
he got the LEDs for free. the mass cost was other (supporting) electronics, microcontrollers power supply, PCBs, tools, mount, etc. etc.

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