Making a POV led Globe

[aliw]

Hi there everyone,

One day I saw a very nice pov led globe on the internet and I thought, I really want to make something like that. (at that time I had no electronic experiance at all) So I went trough the basics of electronics and went some more deep in things I was interested in. I have bought a MiniPov 3 kit by ladyada and went trough every single component on that PCB. (I know that is nothing to compare with when you try to make a RGB Globe POV but I wanted to start somewhere.) With that kit I've tryed many things and I have learned to program C and C++ myself. Read about binary code and Hexadecimal code. So when I was searching on the internet for more information about RGB POV's. I've found a very nice RGB POV of yours on youtube. And thought you could help me out with some problems and buying PIC's.

I have a thing I want to ask first:

How do I decide wich microcontroller I need to buy?

I know how the ATtini 2313 works, so could I do the job with that one?

How do I set the time for each LED to light up because the globe is round. (at the top and bottom the circles are very small and at the middle verry long.

Link to the movie I saw on youtube that inspired me:

http://www.youtube.com/watch?v=4rEIFGvD ... re=related

NOTE: there can be some bad english from me sometimes. (sorry for that)

Hope someone replies.

aliw

[Digg]

Here are some links:

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.

To make something simple may be easy but it will never do everything you ask of it. Put your heart into your projects. Spend a little time do some research and make it do what you want.

[aliw]

Those designs where actually very usefull.

Thanks!

[sdudley]

It appears that these POV's are all the rage.

You guys are drawing my interest and soon I will just have to join in the fun and try to make one for myself!

Stacy

[brad]

Hi, and welcome to the forum!

I myself made a pov globe a couple of years ago, basically stealing the idea from this youtube video:


http://www.youtube.com/v/oLygWkHo9nw


The great thing is that you don't need special seperate timing for the LED's even though they are in a curve. (I.E. the LED's on the 'equator' move much further in the same amount of time as the LED's near the top and bottom poles.)

You just need to program your microcontroller with all those 1's and 0's that make up a world map. Then through the use of tristate buffers and latches. Just send one column to the LED's at a time. Trust me, it will look great, just have one set delay that all the LED's are on for and it will be just fine.

As for which microcontroller, most people around here use some sort of 8-bit pic microcontroller. I did look into atmel a few years ago but finally decided on using pics and it has been great. Having said that, ATMEL will basically still do whatever job a pic can do.

Did you get to see the assembly tutorials I had up on the old site? If not never fear because they will be back online this week.

keep us updated on how your project is coming along.



-brad

[aliw]

First thanks for the answer that came so fast.

Yea, I see now that I don't have to set the time for each led. (Thinking that was a bit dumb of me)

I know that to light one led up i have to put a 1. But is it the same for RGB leds? Because the led has to know what color to light up.

I found this, and thought that this was maybe the way to light the LED's in the correct collors.

http://nl.wikipedia.org/wiki/RGB-kleursysteem

And actually could you tell me how a RGB led actually works? I saw that the led has 3 leads I guess one for red, green and blue.

And to hook up more led's than pins you've got on the microcontroller you've got to use "tristate buffers and latches" I guess. but can you explain what they exactly do and how to hook them up to your IC?

When I was looking at the tins on different microcontrollers I've discovered that somethimes both have an PD1, PD2,PD3....PD5 and PB0 to PB7 pins. does that actually mean that the output of those pins are the same? (what does VVC mean because)

And for the microcontroller. I understand that you advice me to buy a pic microcontroller but wat is the actuall differance between a pic and a 8-bit?

Sorry for some stupid questions but I need to ask them to somebody

[Digg]

Ok first of you have quite a bit of confusion about what it is that is going on with this project. I will try to help you to the best of my abilities but I can not teach you everything you will need to do some more research on your own so that this will make more since to you.

Ok first of a rgb led is three leds in one. There are four pins that come out of it. A common cathode or '-' and an anode or '+' for each color: red, green, and blue. You can turn each one on individual or mix them for more colors. For instance you can turn the red and blue leds on you get a purple color.

Your next question is how to expand your design so that you can have more leds than you have pins. This can be done easily with latches. Latches are useful for many things and can be configured in several ways. The best way I can explain this to you is to tell you to think of them as memory. You can write data to them and it will hold those values until you tell it to change them. So with this in mind lets take a generic 8-bit latch. It will have a data bus which will consist of 8 lines, an enable and a clock. We will ignore the clock function of the latch to make things simple. Most enables are active low, which means that the latch is selected when logic '0' is on that pin. So when the latch is enabled whatever is on the data bus is stored in the latch. Whenever logic '1' is returned to the enable whatever was on the data bus is now stored on the latch and will stay there until you change it. I can go more in depth on this but it would be best if you found a good tutorial about exactly how this works.

You also have a problem with your microcontroller idea. A pic is a brand of microcontroller which is very common and easy to use. There is no such thing as an 8-bit it is a description of the microcontroller. It means that it works on 8-bit at a time. I cant think of a good way to explain this to you at this moment.

So lets look at your project...

You want to make an led globe with lets say 16 rgb leds. You have chosen to use a pic MC for the project. The pic I use most is the 18f4520. It has 4 8-bit ports and 1 4-bit port. Each led needs three lines to control it so 16x3=48. You will only have 36 I/O pins so you will need to use latches to expand your design. You then choose to use 6 8-bit latches to do this. You link all the data lines to one data bus. This will only take up one port, or 8 of your I/O pins. Now you need to address each latch to be able to write to it. There are many ways to do this but I will do it the easiest way possible. You will just use another port for this and connect the enables to the first six pins on that port. To write to any latch you drop the enable pin to logic '0' set the data to whatever you want the return it to '1'.

This is not complicated once you understand how all of the pieces fit together. You should really read brads 8x85 pov project as this will be a great help to you. His project is a bit more complicated than the one that I just explained but the circuit diagram is very helpful for an explanation of what i just explained.

I know I left some things out so please feel free to add to explanation.

Hope I was of some help

[brad]

That just about sums it up there diggs.

It would certainly help if you checked out the 8x85 POV display. There is quite a bit of info there. Also have a look at the 74373 datasheet (which you can grab from the link below)

http://www.google.com.au/url?sa=t&sourc ... 35m6M89xiA



The RGB LED's come in either a common anode or common cathode form. The ones I have been using are common cathode, this means that all three cathodes of the three colour segments inside the LED are connected together, then you have three other connections, one for red anode, one for green anode and one for blue anode.

So you would connect the common cathode connection to ground, then you would connect a resistor to each of the three anodes. Then if you apply a logic 1 to any of those anodes, you will light up that particular colour. you can light up multiples to get different colours.



RGB LED's are fun = )

[Chuckt]

It reminds me of this POV clock using a hard drive motor:

http://hackaday.com/2010/03/20/pov-cloc ... lic-block/

[aliw]

I know what you mean with those common anode and common cathode rgb leds, but what is actually the point of it because there is 1 anode and 3 cathodes or there is 1cathode and 3 anodes. has this something to do with the resistors? (jou have to use 1 in stead of 3)

And I have seen the 74373 datasheed.

I know that when pin 11 (C) is connected the flow from all D pins to Q pins is enabled. And that pin 1 (OC) is used to program it.

But why there are 8 D and 8 Q pins because I want to expand my design. ( I need to connect all D's to get Q outputs) Or I don't need to conect the D pins and use pin 1 (OC) to control the outputs from the Q pins?

I know I wrote something wrong here, so correct me.

Sorry for the late reply. But I was busy at school.

[aliw]

Thanks for the information you gave me.

However I don't understand the latch bit. When I send '0' to the enable everything is stored and when I send '1' to the enable it sends the data to the led's. I guess the enable is the (OC) pin on the datasheed Brad send me. So when I send '1' to the OC pin all that I stored to it goes to the Q outputs. Is this corect?

so lets say I use 3 latches: (one for red one for green and for blue)

red data green data blue data

00000000 - led1 00000000 - led1 00000000 - led1

00000000 - led2 00000000 - led2 00000000 - led2

00000000 - led3 00000000 - led3 00000000 - led3

00000000 - led4 00000000 - led4 00000000 - led4

00000000 - led5 00000000 - led5 00000000 - led5

00000000 - led6 00000000 - led6 00000000 - led6

00000000 - led7 00000000 - led7 00000000 - led7

00000000 - led8 00000000 - led8 00000000 - led8

does this mean that I will need 3 8-bit latche to control 8 rgb leds? (and 6 8 bit latches to control 16 rgb leds?)

does each line have 8 '0' or just 1 '0'?

[Chuckt]

The 3D POV Display I like is this one:

http://www.youtube.com/watch?v=oLygWkHo9nw

[brad]

The 3D POV Display I like is this one:

http://www.youtube.com/watch?v=oLygWkHo9nw

thats the one that had me interested in building one!

[brad]

It reminds me of this POV clock using a hard drive motor:

http://hackaday.com/2010/03/20/pov-cloc ... lic-block/

I started to make one of these but never actually finished it.

did you know that the hard drive platter is semi - transparant. I didn't!

[brad]

Thanks for the information you gave me.

However I don't understand the latch bit. When I send '0' to the enable everything is stored and when I send '1' to the enable it sends the data to the led's. I guess the enable is the (OC) pin on the datasheed Brad send me. So when I send '1' to the OC pin all that I stored to it goes to the Q outputs. Is this corect?

so lets say I use 3 latches: (one for red one for green and for blue)

red data green data blue data

00000000 - led1 00000000 - led1 00000000 - led1

00000000 - led2 00000000 - led2 00000000 - led2

00000000 - led3 00000000 - led3 00000000 - led3

00000000 - led4 00000000 - led4 00000000 - led4

00000000 - led5 00000000 - led5 00000000 - led5

00000000 - led6 00000000 - led6 00000000 - led6

00000000 - led7 00000000 - led7 00000000 - led7

00000000 - led8 00000000 - led8 00000000 - led8

does this mean that I will need 3 8-bit latche to control 8 rgb leds? (and 6 8 bit latches to control 16 rgb leds?)

does each line have 8 '0' or just 1 '0'?

Yes what you have said there is correct, although you actually send a logic 0 to the output enable line to send all eight bits to the LED's. If you keep the output enable as a logic 1, then you will get nothing on the LED's it is a logic low enable pin.

Also, yes you do need three 74373 chips to control eight RGB LED's and six to control 16 RGB LED's and so on.

how is the project coming along?