Best way to use multiple decoders for an LED matrix

Question

I'm designing a 16 x 32 RGB LED Matrix and its controller / driver board. So I've designed a couple of solution approaches and I'm wondering if there is a better way to drive multiple 4 to 16 line decoders ( I am using the CD4514B ) than the solution I'll show in the image below.

---

Some background information:

Simply I want to use two of the 4-16 decoders to end up with 32 channels so I can select/enable ONE row|column of the matrix at a time.

The other row|column ( the 16 pin side of the matrix in this solution ) is selected/activeted by two 8bit shift registers ( times three since RGB ).

At this point I'm not sure if I should control the 16pin side by 2x shift registers and the 32pin side by 2x 16bit decoders OR control the 16pin side by 1x 16bit decoder and the 32pin side by 4x 8bit shift registers.

I am also not shure if I should/can split the matrix into 8 individual 8x8 matrixes, and why I should do that...

Since I dont even know which AVR I'll be using as the main unit at this point, I don't know how many IO pins I can use. Even if I want to keep the size and costs as down as possible, I dont want to run into some timing / speed problems. And that is the point - I dont know which design suits the best, because I will need many shift registers in a tree-like-structure when I want to use a small AVR like the ATtiny45 ( 5 IO pins ).

So If you have some ideas / experiences about this, please tell me.

---

But to come back to the original question, here is my thought about the dual 4-16 decoders:

What do you think about it ? Is this the common way to do this ?

For sure, for chaining more than 2 decoders, I could simply use another ( e.g. 3 to 8 bit ) decoder, just to control the inhibits, but for this one I'm dealing with only two.

Thank you for your help.

Answer 1

That's exactly the way it's done, as long as you don't want to turn off all the LEDs at any time. If so

^{simulate this circuit – Schematic created using CircuitLab}

will allow a master inhibit to override the select line.

Answer 2

The degree to which you choose to matrix the LEDs has to have more consideration than just the minimum complement of I/O pins needed. You also need to consider the duty cycle of each LED. With your proposed dual 4-16 decoders you will only have a 1/32 duty cycle of the LEDs in each column. This can have a serious impact on how bright you can get the LEDs to light. As a minimum you end up having to boost the peak current into the LEDs to a quite high level.

My experience is that you would have a lot better success with a duty cycle of 1/8 or greater.