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Topic: Pull downs, transistors and LED's (Read 1 time) previous topic - next topic

CrossRoads

I'd say you need to get the right tools for the task, in this case the right chips.
I'd suggest a uC with more IO, and a current sink chip that will be way less tedious to wire up than all those transistors.

I'd go with a chip in the 40 pin '1284 series, with 32 usable IO pins. Keep D0, D1 free for messages from a PC, or sketch downloading, or use as input switches.
Wire your anodes in parallel as  columns, and wire the cathodes in parallel as rows.
Store your pattern to display in an 18x12 array.
(1284 has 16K SRAM too, can store several)
Write a simple loop to multiplex thru the LED array:
Code: [Select]

void loop(){
if ( millis() - next_udpate) >=on_duration){
next_udpate = next_update + on_duration;
turn off current cathode
next_row = next_row+1;
if next row == 12, next row = 0;  //reset back to top
read next array row, write the anodes, drive next cathode low
}
and while waiting for next refresh time to occur, can be checking for serial message, change the array, read buttons, etc
}


Make sense?
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

pYro_65

Hi CrossRoads,

My initial non rgb prototype was done on a mega, but in an effort to understand EE concepts more than my current level I set my self a challenge. I also have little need for ram as the patterns I wish to display can be generated quickly at run time. However as I add more peripherals I many need more ram to work with, and my mega is still an option. But for now I would like to stick with some variation of my original design. Next year I hopefully can get into a uni course, and I would like to have a bit of practical experience under my belt.

And at the moment the led grid is only half the size I intend to work with. I might also put an order in for a 1284 just to check it out.

Docedison

Knock off Chinese 2560's are about $20.00 - $25.00 now... on Ebay. The ones with 8U USB devices... Just a thought. mine was a freebie from a friend there, even says Arduino on it, that's why it was a freebie. Name copyright violation. Seems to work ok, once everyone here held my hand so's I could get it working (USB Driver issues and my stupidity. For as long as I have been working with PC's I should not have been fooled that way). Bought a $15.00 Uno for the same reason... They (Ebay pulled it) Right after mine was shipped, Go Figure.

Doc
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"The solution of every problem is another problem." -Johann Wolfgang von Goethe
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CrossRoads

Ok, fine, you want a challenge, I can accept that.
You still need to wire up things correctly so current can flow.
I think you need something like this, and then have your 2nd layer of transistors controlling the multiplexing of the transistors.
Low turns on the PNP transistors, High turns on the NPN transistors.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

CrossRoads

The end result would be something like this where transistors controlled the muxing of a 5x5x5 cube.
You are changing the control with the addition of the PNP transistors.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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