3x10 led matrix

Projects General Guidance
1

Hi all, I'm currently working on a project where I'd like to have two bar-like matrices of 3x10 leds for some lighting effects on two sides of a box. I'm going at this with no formal training and have only picking up a formula here and there, so endure the simple questions.
I did research for a few days, but I'd just like a little individual project guidance, what I guess this forum section is for.

Some info:

  • I don't need to control them individually, I just want to turn all of them off and on and control brightness (I'm getting audio levels from a mic and want to adjust the brightness accordingly)
  • I have limited space, about 2 x 4 cm on which to put chips, so I'd like a chip that does it all and that I can chain two of if needed
  • Leds are these rgb rainbow leds with timer chip and only two pins. Max Voltage: 3.8V, Max Current: 30mA. If it helps, here the link where I bought it from (all in German sorry): http://ebay.eu/1asnT4E

So, what have I tried/done: I started with the common 74HC595 shift register, thought I could just daisy chain two of them. I then found out I'd need some transistors to sink the current(?) and even with a darlington array that would again exceed the space. Then I looked into LED drivers like the MAX7219/MAX7221, getting lots of info from here http://forum.arduino.cc/index.php?topic=53152.0, which I guess would be the logical next step. But then I had this thought whether it'd be possible to put each of the three rows in series and just connect the last led pins through some resistors/transistors to the Arduino, although even looking here http://forum.arduino.cc/index.php/topic,12429.0.html didn't really answer my question.

So, summing up:

  1. Is it possible to use the Leds in series through some resistors/transistors like I suggested? That would mean 6 rows (2 matrices remember) of 10 leds with pretty high values connected to the Arduino Uno. I don't know much about EE yet, but I guess that's absurd? Or not? It'd be the easiest for me that's why I'm asking.

  2. If not possible, what driver chip would fit for this kind of matrix? From what I gathered the MAX drivers are awesome all-rounders, also for this type of 3 x 10 matrix? Chaining two? Is this the most efficient solution then?

Thanks a lot really to anybody, I usually just research the hell out of something but the questions and uncertainties stacked up with this one, thank you :slight_smile:

2

You haven't really described what you want, or at least not very well.

The first problem is that you refer to flashing (and/ or fading) LEDs. I have a pack of 50 or so here, really very disappointing. It is meaningless to talk of "controlling" them in any way other than on or off. You cannot control their brightness, and you cannot drive them with a MAX7219 as you would be switching the power off and on and that would not work with the PWM driver chip inside the LED - hard to predict exactly what will happen.

You cannot put them in series either, and they - unlike almost all other LEDs, require a constant voltage, not a constant current.

So, if you want to turn them on and off, you need to do that with a transistor from the Arduino ports. Let me give you a hint - up to six transistors takes up less space than the MAX7219, though you do need resistors to go with them, you also need at least one resistor with the MAX chip. If you could use a SMD MAX7219, well then you could use SMD transistors.

Actually, you probably want a TPIC6B595 to drive the LEDs in parallel groups.

If you were to go to more simple LEDs, yes, you could drive all 60, even multi-colour ones, from the MAX7219, either individually or in banks, given that it has sixteen brightness steps which affect all LEDs at the same time.