LED Matrix 32x8

Hello all,

I entered arduino's world some months ago just to use it as diagnostic tool for my network devices.
Anyway, i decided to start a project using arduino and a bag of Leds. :stuck_out_tongue:
I made a matrix 32x8 common cathode.I use 4x 74HC595 to drive each column - anodes.
So, i plan to use TPIC6B595 to drive each row - cathodes.Do i have to connect directly the rows on TPIC6B595?
The general idea is correct or not?

That's the main question.I'll explain more, after your feedback.

Thank you

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Yes - each 6B595 output connects to one column of cathodes.

So either 1 74HC595 and 4 TPIC6B595 (32 across by 8 high)
or 4 74HC595 and 1 TPIC6B595 (32 high by 8 across)

So this way will work,right?

Each row will connect directly to 6B595 or should i put a resistor inbetween?

Of course, four MAX7219s would do the job really easily.


from 7219 datasheet - DIG0–DIG7 Sink Current…500mA
when my row can be 640mA some times. not sure if it could be safe enough for that

Edit: 640mA/4…u r right

Yes, each 74HC595 output will need a current limit resistor - keep current to 8-9mA so you don't blow the chips 70mA max current rating on the Vcc pin.

4 MAX7219 would be cleaner - only 8 outputs are on at a time, multiplexed at 800 Hz rate.
Just write the data into the register that represents an 8-bit column, it does the rest of the multiplexing for you.
These are likely counterfeit parts (Maxim said they are not an authorized distributor), but I've not had any that didn't work yet:
Arrange the 8x8 groups as 4 across, or 4 vertically.
See the parola library to drive them, or roll your own like I did here:

LEDs need 20mA each. 8-9mA looks to low,no?

If you are using 74HC595 to source current, the chip has an Absolute Max rating of 70mA on the VCC pin. If you want to source 20mA from 8 pins, that's 160mA, you will smoke the part before too long.
With high brightness LEDs, 8 mA should be plenty. Do some tests before you get too carried away with your wiring.

Need a resistor on each of the output of the 74HC595s.
6B595 will then sink whatever outputs are on.
If you are sinking 32 outputs @ 8mA each, that's 640mA, I would suggest 8 N-channel MOSFETs instead, AOI514, AOI516, AOI518 from digikey.com
a 5th HC595 can be used to control their gates.

This board for example has 32 of those MOSFETs with 4 74HC595 to control the gates

my LEDs are ultra brightness,so i will take a look soon

So, as long a full row needs 256mA if i limit leds @8mA, i will split the rows using 2x 6B595.
Then i’ll have 2x 16x8 joined matrices.
Seems the MAX7219s choice is not so bad, but i will try my way :stuck_out_tongue:

Wrong way to look at it phrase it - a full row needs to have 256mA sunk to turn on all LEDs on at desired brightness. In context, what you said is clear tho.
TPIC6B595 can't sink that much, hence the suggestion to use AOI514, etc.
Or use two outputs, each sinking 128mA.

That's what i said.
I will split the 32x8 matrix to 2x 16x8
so the sink max sink current to 6B595 will be 8mA x 16 = 128mA

Agreed. I just answered somewhat awkwardly.

One more idea i just had.
What if i add one more 74hc595 to expand the columns to 35, increase the current to leds @ 10mA and add some 2N3904 @ 6b595 outputs?

2N3904 can handle 200mA, when my rows reach 170-180mA each
and 595 can handle 75mA, when my columns reach 70mA

to CrossRoad: I'm trying to find a way to solve it because i don't own AOIs :slight_smile:

Well I did say …

Well I did say ...

you just made my day...or night anyway... :smiley:

Hello community again,

i came back with some new questions as i moved my Leds to 8x8 boards and now it's expandable and rotatable, that means i can add more 8x8 boards and rotate the polarity.
The question is...what is better for single color leds?common anode or common cathode?
I saw enough posts about "there is no common anode or common cathode for single color leds" but what is the best option for a long 8x... led matrix?
My goals are... long life time...short display time

Components i use:
595s + BD135s for cathodes
595s for anodes

i have so many options about the order of my components but i ask you about your experienced opinion

The question is...what is better for single color leds?common anode or common cathode?
i have so many options about the order of my components but i ask you about your experienced opinion

Which to use depends on your strategy.
In your paradigm, in your application - do your columns require sinking or sourcing?