Use of a PIC

[Edwardo]

An absolute newbi with PICs, I would like to make a LED display in a dome, using about 1200 -1500 LEDs. It has to turn on all at once for a few minutes, then rotate, run in different patterns...etc.My question how do I drive all the leds on using a PIC and supply enough current to light them fully? Can anyone help please?? Ed

[HenrikOlsson]

Hi Edwardo,

My question how do I drive all the leds on using a PIC and supply enough current to light them fully?

You don't.... what you need to look into is called multiplexing and is basicly how all LED-signs work. From your alarm clock radio to the huge displays at Times Square. Let's take the alarm clock as an example. Basicly the LED's are arranged in groups, you then set the pattern for that particular group and then turn them on. After a short amount of time you turn that group of LED's on and turn on the next group. If this is done quick enough the human eye/brain will not be able to see that they are actually flashing. In order to keep the brightness of LED's up the current thru them is usually many times higher than the maximum continious current for the very short period they are actually on.

With that being said 1200-1500 LEDs are a LOT of LEDs....Not that it can't be done with a PIC but I'm not sure it's a very good beginners project. Instead I sugest you get 1 LED to turn on and off at your command, then move up to 8 leds connected to portB (for example). When you have that working you can rig a 8*8 matrix and see if you can that going. From there the you could possibly move on and rig a 4*4 matrix of 8*8 matrixes to get 1024 LEDs.

Another tricky thing to keep in mind is how to store/retrieve/output the pattern that you want to display.

Here's a link showing how it's done (not with a PIC but anyway):
http://www.fpga4fun.com/Opto5.html

Welcome to the forum!

/Henrik Olsson.

[Edwardo]

Hi Henrik, Thanks heaps for the quick reply, didn't expect it so soon. I will be looking into multiplexing as per your suggestion. Have been able to run 8 LEds lighting from LSB to MSB and back with a pic ,but thats about it. I'll BE BACK !! Cheers.

[HenrikOlsson]

Edwardo,

Have been able to run 8 LEds lighting from LSB to MSB and back with a pic ,but thats about it.

Well, then you're in pretty good shape! There are dedicated multiplexing chips you could look into to. The MAX7219 for example is such a chip. It can drive up to 64 LEDs and you can cascade them to increase the number of LED's or connect each of them to different PIC pins. There's another thread active at the moment discussing cascading multiple MAX7219. Still, 1200-1500 LED's are a lot of LED's....

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1339

/Henrik Olsson.

[BigWumpus]

What LEDs do you want to drive ?

3mA, 10mA, 20mA, 350mA, 700mA, 1000mA ???

You should divide your problem into smaller units an adress them from a central processor or so...

[syscoder]

i have also some projects like that and i used led more than you(23450 leds) i have used led 350ma rgb leds with 16000000 colors for animations.

what is your project if you can explain it i can help