Making a POV led Globe

[bitfogav]

Heres a diagram of basically how to connect a 74373 to a pic16F628a..
has you can see that you need to connect 8 pins of the 16F628a to the 8 D-pins of the 74373.

Dont forget though that you also need to connect pins 1 and 11 of the 74373 to your microchip to latch the data and enable the 74373 to output your data.

note, the blue line from the 74373 to the 16F628a is actually 8 connections or wires, depending on your project

[brad]

Yep, that looks good.

The 74373 is essentially an 8-bit parallel shift register, with the added extra of tri-state outputs.

aliw - what do you mean exactly when you are talking about just the one wire?

[bitfogav]

Im guessing aliw means that he is trying to send 8bits of data down one wire or one pin of the microchip? in this case the 74595 would work with that setup

[brad]

Ah, I see!

Do you not have enough pins on the microcontroller to be able to do it via parallel?

[aliw]

Ok, I just don't understand how to connect the 2 IC's. What I understand is that I need to connect 8 pins from the pic to the 8D pins of the 74373 separately. But what is the point when you do that? (as you don't expand your design at this point. When you just use one 74373.) Can you just connect those 74373's in parallel?
I will make some demo schematics, and I will be grateful If you tell me which one is correct. (As for my project I am going to buy 100 GRB's so I will be just using 96 because 96/8=12 and 12*3=36 so I will need 36 74373's. Is it actually possible to connect those 36 74373's on one PIC microcontroller?)

demo schematics:

http://www.bradsprojects.com/phpBB2/download.php?id=33
http://www.bradsprojects.com/phpBB2/download.php?id=34
http://www.bradsprojects.com/phpBB2/download.php?id=35

sorry for ugly paint lines. what program are you actually using to make these schematics?

[brad]

Yes, the last one is right!

http://www.bradsprojects.com/phpBB2/download.php?id=35

you can connect 36 of the 74373's to the same 8 pins from a microcontroller (as long as the microcontroller has enough pins to then be able to address those 74373's)

So in the example of the link above, you have two 74373's both connected to the same 'data bus' of the microcontroller, this means that what ever data is on those 8 connections, both of the 74373's will have that data on their inputs, you then send a logic 1 to the 'C1' connection of the particular 74373 that you want to store that data.

So in the example of using 8 RGB LED's, you would need 3 of the 74373's.

You would connect all 74373 inputs to the same 8 pins of a microcontroller. you would first send out 8 bits for the red leds. even though all three 74373's receive that data, you would only send out a quick logic 1 to the red 74373, C1 connection (this will save those 8 bits to that 74373.). you then send out the 8 bits for green, then send a quick logic 1 pulse to the green 74373, then you do the same for blue.

then when they all have their data stored within them, you then send out a logic 0 to all three 'EN' connections. this will then send all the data stored in the 74373's - to the LED's

[bitfogav]

Basically to run 36 74373's chips you will need a microchip with atleast 80 outputs/inputs and as far as I know in the 8bit range there isnt one available at this moment, you would have to use a 16bit microchip.

the other option is to use a completely different design for an example
the project below.

[TestSubject421]

I have started working on a POV Globe and was wondering what calculations you used to design your images.

Did you start by breaking down the RPM to microseconds per rotation
then figure out what kind of "pixel resolution" the POV has
and continue on that path to figure out the proper timing for the duration of on time of the LEDs?

Or what method did you use? (i am sure you have mentioned it some where i just have not found it yet)

Keep up the good work!

I am open to any input even if some one out there has a good guess
It has been a slight headache for me but i could be making it harder than it needs to be (one of my bad habits)

If you wish to see a pic of the primitive prototype

http://s3.amazonaws.com/data.tumblr.com ... 47QfuW4%3D

Sorry about the Unrotated image and you can ignore the pickit dangling ohh and ignore the 1 unwired LED thats been fixed.
I am using a 16f690 for the MCU, 2x 3V lith button cells for power, a glass tube for my "axel" that was flared and....(kill me) hot glued onto the motor shaft, 28 green RA LEDs (14 on each side and they are mirrored, look at the pic and the wires if you dont quite understand)
ohh and the motor is a 110VAC fan motor (incase anyone wondered)

[brad]

You really don't need to do any calculations at all.

Just work out your picture - send the data to the led's and just guess a delay between each column and then spin it up, see how it looks. then just use a little bit of trial and error for five minutes to adjust your motor speed / delay routine to get the best picture possible.

I have never actually used two sets of LED's like that. Are you planning on having the same image 180 degrees apart? or are you trying to fill in the gaps on every half rotation?

Let us know how this thing is coming along.

[aliw]

First sorry that I wasn't here for a long time but I was on vacation and unfortunatly there was no internet connection. =(

bitfogav wrote:
Basically to run 36 74373's chips you will need a microchip with atleast 80 outputs/inputs and as far as I know in the 8bit range there isnt one available at this moment, you would have to use a 16bit microchip.

Can't I just put all 74373's in parallel on porta and put all enables and clock enables on other 74373's? (As I was writing this I became aware that this maybe can be done easyer )
Or is it better to use a 16-bit microcontroler because there is more storage in there?
I'm sorry but I am new to the microcontroller stuff so please tell me something about the 16-bit ones.

[brad]

First sorry that I wasn't here for a long time but I was on vacation and unfortunatly there was no internet connection. =(

bitfogav wrote:
Basically to run 36 74373's chips you will need a microchip with atleast 80 outputs/inputs and as far as I know in the 8bit range there isnt one available at this moment, you would have to use a 16bit microchip.

Can't I just put all 74373's in parallel on porta and put all enables and clock enables on other 74373's? (As I was writing this I became aware that this maybe can be done easyer )
Or is it better to use a 16-bit microcontroler because there is more storage in there?
I'm sorry but I am new to the microcontroller stuff so please tell me something about the 16-bit ones.

Yes you certainly can have loads and loads of 74373's connected to a common bus and then use extra 74373's to control the latch enable of the 74373's that goto the led's.

I have done exactly that in a circuit I was working on last year.

I cant remember exactly what I was doing with it, but I needed to control a whole heap of outputs and so I used loads of 74373's, but then didnt have enough I/O pins to control them - so i used more 74373's to control the other ones.

It is messy but it works.

[aliw]

Does a 16-bit pic microcontroller just have 2 times more outputs as a 8-bit pic microcontroller, or its got 16 0's (0000 0000 0000 0000) as an output of one pin?
I want to make my circuit small (as small as possible) because it needs to be on the rotating part of my pov. (in the center)
so please give me an example of a 16-bit pic microcontroller and tell me the differences.

[aliw]

I guess i will need a 16-bit parallel shift register instead of a 8-bit one or can i just connect two of these?
Is there a way that I can read these names so I know what they actually do? for example "74373" that doesn't tell me much. or for the microcontrollers "16F628P" or "18F4420".
And what is the name or where can I find a program to make these schematics?

[brad]

I guess i will need a 16-bit parallel shift register instead of a 8-bit one or can i just connect two of these?
Is there a way that I can read these names so I know what they actually do? for example "74373" that doesn't tell me much. or for the microcontrollers "16F628P" or "18F4420".
And what is the name or where can I find a program to make these schematics?

To keep things nice and simple, I would stick with an 8-bit microcontroller. They are more than powerful enough to make a POV display.

Those numbers specified above tells you alot! just type in one of those part numbers into google followed by the words datasheet - you will then be able to download (normally in PDF format) the datasheet that contains all the info you need for the chip.

As for drawing schematics, you can download eagle schematic editor for free which allows you to draw schematics, just like you see on my site.

[aliw]

Ok but for the 96 led's I will need to use 74373's for the enables that gives me a headake because it's a little messy. so is there a way to make this simpler? (that I don't need to use 74373's for the enables?) Hope there is


and I know that when you type in the part number in google the whole datasheet will come up. But what I ment was that the numers itself tell you something for example 18F4420. that the 18F means that there are 18 output pins and 4420 is the ram of it or something.(I know that wat I just wrote here is completely not true but it is just to make the question more understandable.)