Creating an 8x?? RGB POV display

Post here to discuss the 8x85 RGB LED POV Display.

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Digg
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Creating an 8x?? RGB POV display

Post by Digg » Sun Mar 28, 2010 1:28 pm

Hey everyone,

I am working on a RGB pov for my micro controller lab. I will be using the Pic 18f4520. This is the pic that we are working with in the lab so we have several that can be used for this project. I have a few questions about the general idea of a pov.

What is the best way to set up the timing for the led's and do you need an external clock? I was thinking that I would set up a variable speed dc motor and tune it to the timing of the led's to create the correct pixel size. I am guessing that this would be the easiest way to do this and would allow for the fastest rotation speed. To me this would give me the highest light level from the "screen".

I was also wondering what would be the best way to drive the led's? The pic has 4 8-bit ports so I could use three of them for each color of the led's. The problem lies in the fact that I think I will need to use port B for the interrupt that would trigger the start of the display. This will work out fine as I can use port A, C, & D but port A has the clock on it. Would it just be easier to drive the led's off of some latches? This would also allow for expansion of the display to 16+x?? by just adding more latches and led's.

Getting power to the device will also be a problem, as putting the batteries on the device would make it hard to turn it off. I have seen this done through an earphone jack and socket being used as a pivot point. If there is another way that someone can think to do this in an easier fashion please let me know.

After seeing several video's on the net and reading the information about the projects along with reading Brad's project about a year ago, I believe that the way that this type of display works is by having a sensor that tells the device that is at the beginning of the display. This I have seen done several ways but I think I will use an led or ir led and sensor to do this. To display something you just send the 8 bit codes to the led's one after the other in time with the motor. The larger the radius of the device the longer you can make the display.

If anyone has any further tips on how to create a project like this it would be greatly appreciated. I will be doing the project in assembler. I should not struggle with the coding on this project as much as just getting the hardware down. If you notice a mistake in my typing let me know and I will fix it.

Thanks Brad for giving me a good place to ask these questions. I also cant wait for you to finish posting your projects so I can go over how you did this project again.

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Post by brad » Sun Mar 28, 2010 1:29 pm

Hi there Digg,

It is taking a while for me to get the content transferred over, mainly because I don't have a whole heap of time to dedicate to doing that at the moment. But it will be up within the next few days.

Now, POV projects are great! I am actually working on a new 8x85 which only uses 1 IC (an 18f4550 microcontroller) whereas my previous design used 7 IC's to do the same job.

Also, my new design will have a wireless receiver and transmitter so that I can control the display wirelessly (eg for changing the picture / animation and also for playing games)

The great thing about designing these displays is that you can just guess what delay you want to use and see how it goes. if the image stretches too much, then you decrease your delay and vice versa.

You also don't need to know the exact motor speed. just turn it on, have a look at the image and decrease the speed (by varying the voltage to it) if the image is too small, or increase the speed if it is too large / wide.

As for the sensor - you don't need an interupt since there is plenty of time to check any pin that you want (using a loop)

In my new design I am using portb (8bit port) for red, PORTD (8bit PORT) for green and PORTA (6bit port) for 6 bits of blue and PORTE for the remaining two bits. Then you would need just one transistor to turn all the common cathodes on / off.

I will post details of my new design soon. but It will be loads better than my old one.

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Post by Digg » Sun Mar 28, 2010 1:30 pm

Well I guess that I am not the only one wanting to make a pov. Due to this I will post some links that i have found useful to me while researching this device.

This link is to an led globe project that I found useful plus there was another person that was wanting to make this in another section of the forum. It is not Pic based but does have a good walkthrough on how they made it.

http://code.google.com/p/povglobe/

This link is a horizontal pov that I also found useful but again is not pic based. But does have several sources that are useful.

http://akikorhonen.org/projects.php?action=view&id=216

This is yet another non pic based design but has a wireless connection to a laptop. It is a propeller type display. It is documented quite well and if you wanted to get really in advanced in your design this could help.

http://courses.cit.cornell.edu/ee476/Fi ... index.html

This site has a few pov designs but are really simple and some are pic based. To see the rest look under projects

http://www.ladyada.net/make/spokepov/

This one is another bike wheel design that was done on pic and has a walkthrough of the project.

http://drewish.com/blogger/archives/200 ... v_toy.html

Yet another bike pov but has several versions but is not pic based.

http://johndawson.org/projects/POV/POV.php

This is just something that is posable to do with pov displays if someone is willing to put enough time into them.

http://hacknmod.com/hack/bicycle-wheel- ... -displays/

This is just a thing I found that I just could not help but share. Get this to work well and here comes the $$$

http://blog.makezine.com/archive/2006/0 ... our_c.html

While there are many more projects out there, I really like these and thought I would share them with all of you.

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Post by brad » Sun Mar 28, 2010 1:30 pm

hat's a great list of links, I think I will add a links page with handy links just like that.

Im not sure I would like to drive my car around at night with POV wheels though = )

Image

What would be really cool though would be to make a huge 2metre diametre ring with approx 1,000RGB LED's faing inwards. then you would have a standing platform in the ring and you stand inside with the ring spinning and creating a 3D world around you. now that would be cool = )

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Post by TestSubject421 » Sun Apr 04, 2010 6:07 am

brad wrote: What would be really cool though would be to make a huge 2metre diametre ring with approx 1,000RGB LED's faing inwards. then you would have a standing platform in the ring and you stand inside with the ring spinning and creating a 3D world around you. now that would be cool = )
Ohhhhhh my, time to get to work!

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