LED Matrix?

Forum 2005-2010 (read only) Hardware Interfacing
1

I just received my first LED Matrix (link) and am wondering on how interface it to Diecimila? Any hints or resources would be highly appreciated.

Thank you :slight_smile:

2

Searching at http://www.arduino.cc/ search box, I found posts like this:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1203615068/9

and pages like this:
http://www.arduino.cc/playground/Main/MultiplexMAX72xx

I'm sure you can find more doing the same.

Good luck.

3

Thank you :slight_smile:

What would be my options if I could not find MAX72xx chips?!

4

You could use 74HC595 shift registers, but the MAX72xx chips are much easier to use. You can find info on the shift registers here or on the playground as well.

You can do one colour easily enough using 16 IO lines on the Diecimilla, but remember the 40mA current limit on the ATmega IO pins, so you'll need transistors to drive the matrix.

5

You could use 74HC595 shift registers, but the MAX72xx chips are much easier to use. You can find info on the shift registers here or on the playground as well.

You can do one colour easily enough using 16 IO lines on the Diecimilla, but remember the 40mA current limit on the ATmega IO pins, so you'll need transistors to drive the matrix.

Probably only one LED is ON at any given time, so you don't need to worry about using transistors... but evaluate your needs and the resulting circuit before frying your Arduino.

6

I got a max7219 here:

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDisplay?langId=-1&storeId=10001&catalogId=10001&type=index

Type part #312160 into the Jameco part # search.
I don't think they have the 7221.

Additionally their free catalog makes for good bathroom reading material :).

7

Probably only one LED is ON at any given time, so you don't need to worry about using transistors... but evaluate your needs and the resulting circuit before frying your Arduino.

That means at most each LED is on 1/64th of the time, so you might have a problem with brightness. I'd do 1 row at a time so the LEDs are on 1/8th of the time, so you would need transistors along the rows at least.

1/64th duty cycle might actually work. I built a fairly large display (multiples of 160 LEDs) a while back and power was an issue so I did some experimenting, and it seems like 1/10th duty cycle looks like almost full brightness, at least to my eyes. So in that project, I PWM'd the LEDs in separate groups simply to keep my total power consumption under 2 amps.

8

fargo,

If you are going to use 2 MAX72xx to drive that RG matrix there will be no need for transistors.
I have a similar matrix (but the bigger "medium" Sparkfun size). I just tested it by lighting both the red and green "continuously" via the 2 MAX7221 chips. The current required to drive the chips and the matrix measured 93mA.

(I'm using a value of 26K for rSet and the intensity was set to max.)

I guess the 40mA limit that Oracle mentions is pertinent if you decide to use shift registers.

A few notes - if you decide to use the MAX72xx . . .

  • If you go to the Maxim web you can get free samples
  • If you get samples, get the 7221 (see the Playground article Akashi mentioned)
  • Note the pin outs for your display are different than the diagram in the Playground article
  • The 7219 has worked just as well for me, so if you buy those (they are cheaper and more common) you should be OK.
  • If you want sources, tell us for what country.

I've had fair bit of experience with the 2xMAX72xx and they work great for me in RG 8x8 matrices with no PWM ("dimming"). I've had no experience with the shift register approach, so I can't state any opinion on which is "better". (Having said that, my hunch is that the MAX will be easier in your case. )

If you tell us what you want to do with matrix, that may help too.

9

Thank you guys. All what I need is to lit 4 leds a time till all the matrix is on. Only ONE color.

Now do I need:

1 MAX7219,
1 MAX7221,
2 MAX72xx,
1 74HC595, or
No extra ICs at all?

What about transistors? Also, what is the voltage for capacitors in this article: Arduino Playground - MAX72XXHardware

10

fargo,

The method you choose is your decision!

IMO . . .
The responses here should have given you what you needed to make that decision - or at least, ask intelligent follow up questions regarding them.
Your list of options show you haven't put much thought or research into these responses.

For example, you have a 2 color matrix but you say you only want 1 color. That's cool.
Should you get 2 MAX72xx? Well, you don't need 2 to drive 1 color, right?
(Perhaps you don't know that 72xx means 7219 or 7221.)

MAX7219 vs. MAX7221 ?? - info on the difference is in both of the Playground articles you read (?) and more info was in my last post, right?
So your question is ???

I don't mean to be hard on you. From your question about capacitors, I can tell this is new to you. However, I think you will find that people are always willing to help until they suspect that you just want a "hand out". Then they feel like they work at the drive in window at a hamburger stand.

Check into what the voltage rating on capacitors means and you will have an answer you won't forget.

11

Thanks again and sorry for asking dump questions :-[ Actually, I touched these things only in a course at the university 13 years ago. I almost forgot about everything related to electronics :cry:

After reading all the posts here and articles from playground, I know now what I need: MAX7219, 2 Capacitors (10V or more 100nF and 10uF) , and 28.0k[ch937] Resistor.

12

Bingo! :slight_smile:
Now you have the option of using the Matrix or the LedControl libraries to talk to the chip.
(I'm personally biased toward the later, but either will work just fine.)

Good luck.