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### Topic: 200 LED's how to make it happen (Read 2914 times)previous topic - next topic

#### twelch

##### Feb 26, 2014, 09:29 pmLast Edit: Feb 26, 2014, 09:41 pm by twelch Reason: 1
Okay so I am going to be a stereotypical nerd and make a TRON suit, its not for me its for my son he is 8 so its okay. My first thought went immediately to EL wire, but after some reserch I decided I didn't like the idea of him running around with the power inverter strapped to himself. I did some playing and found I can light up some standard icemaker tubing in 4-6" sections by shoving an LED in each end and it looks kinda cool. I want to do some effects with my arduino and I think I have that all figured out but I need help figuring out how I am going to wire all those LED's together. Much research has gotten me to the point that I know what LED's I want to use, they have a forward voltage of 3.3 and a forward amperage of 30mA. A little math tells me (this were my confidence starts to dissapate) that I can run 2 LED's in sequence with a 100 ohm resistor and as many sequences in parallel  as I want. Now I know that the more I have on there the faster my battery will drain, I was hoping that someone could...

1. tell me my math is good

and

2. give me an Idea of how many LED I can power with one battery if i want them on for 2-4 hours

quick edit - I am not married to the 9v battery other batteries are an option.

#### Paul__B

#1
##### Feb 26, 2014, 11:33 pm
OK, well for starters, you do not - or should not - need the whole 30mA continuously for each LED.

That given, the answer is multiplexing - driving the whole 30 mA (or in fact, 40 mA) for one eighth of the time.

What you want to use is the MAX7219 which will perform all the multiplexing for 64 separate LEDs, powered by 4.5V from three alkaline cells - you could use "C" or "D" cells.  Controlled of course by a Pro Mini.  I am not sure whether you really want to drive 200 LEDs, but three MAZ7219s chained - still using only three control pins of the Arduino - gives you control of 192 separate LEDs.  Each chip requires only a single current setting resistor and the bypass capacitors.

#### twelch

#2
##### Feb 27, 2014, 05:46 pm
thanks paul, 200 is rough estimate, I have to more definite measurements and finalize my design to get an exact number. I was actually considering using four "zones" on the costume so I could add some extra features like flickering the arm if i hit him on the shoulder and the light dimming or shutting off when his identity disk is removed. I am planning on six inputs ( one contact piont for each limb, one for the chest, and one for the identity disk) and four outputs (to provide independent control of each quadrant). All of the LED's in a quadrant will act as one. I am going to check out the MAX7219 but I really have no clue what it is...

#3
##### Feb 27, 2014, 06:35 pm
MAX7219 is basically 8 shift registers in one chip, each shift register controls 8 LEDs.
To save on IO pins, it multiplexes the 8 outputs.  The LEDs are set up with 8 anodes connected going to 8 rows of LEDs. The 8 columns are then turned on one at a time to allow a group of 8 LEDs to light up. The chip does the switching to drive the anodes and sink 1 cathode very quickly and controls the current, so all your code has to do is update a register whenever you want an output changed.

I've been thinking about making a breakout board so that a MAX7219 could be connected to 64 pairs of 2-pin connectors to make driving spread-out LEDs easier. Maybe I'll get that done sooner than later so you can take advantage of it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### fungus

#4
##### Feb 27, 2014, 06:37 pm
Why not use LED strips? Much simpler than messing about with resistors, multiplexing, etc.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### twelch

#5
##### Feb 27, 2014, 06:56 pm
first i don't know what a shift register is, so i will be doing some more reading tonight, second i considered using strips and have not completely written them off but i haven't found ones that i can run from a small battery pack (yet) and they don't offer all the flexibility i would like. I am still playing around with different methoda of diffusing the light to get the even glow i am lloking for and so far the individual led's are winning. i don't mind the extra work to get the end appearance right.

#6
##### Feb 27, 2014, 06:58 pm
So for example the breakout board would have the MAX7219 chip and 64 pairs of holes that an LED would connect to (32 shown here). The LEDs could be on long leads that solder to the holes, or the holes could be female headers that the leads from the LEDs could plug into for a more modular approach:
http://www.pololu.com/product/1028
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#7
##### Feb 27, 2014, 07:03 pm
Individually addressable LED strips would also work. Could be fixed spacing, http://www.adafruit.com/products/1460
or could be individual LEDs on boards that would all get daisy chained together.

The software is more involved, but I think Adafruit has libraries worked out for it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### fungus

#8
##### Feb 27, 2014, 08:19 pm

Individually addressable LED strips would also work.

If the requirement is "small battery pack" then it's unlikely...those things need a lot of amps.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#9
##### Feb 27, 2014, 09:48 pm
Yes, need amps, but no power inverters or anything. Just a Lipo battery pack. Most have built in rechargers.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Paul__B

#10
##### Feb 27, 2014, 11:17 pm

If the requirement is "small battery pack" then it's unlikely...those things need a lot of amps.

That is what I was thinking.

#### twelch

#11
##### Feb 28, 2014, 10:57 pm
Small is relative, I mean I'm okay with a couple of D cells but I don't wan't to have to pull a car battery around in a wagon.

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