8x8 Dot Matrix LED pull up resistors?

[betwixt]

It might work, you are using the 'HC374 as a shift register. I would have to do some serious timing simulation to see if it meets the necessary set-up time requirements.

However, to use 22 ICs to drive a single 8*8 LED matrix is HUGE overkill and even with that many ICs, it still has a 1/8 duty cycle.

What is your end application? If I was asked to design a single 8*8 display I would do it in one IC, if it needed a very large line of displays, I would use dedicated display drivers.

Brian.

 

[KlausST]

Hi,

To drive a 8 x 8 LED matrix
* you could use the suggested MAX led driver IC.
* or you could use a microcontroller and 2 driver ICs for one display.

So why do you make it that complicated and draw schematics with 20 ICs?
What idea is behind this?

***
I'd go for a 1:8 MUX rate.
Generally for multiple displays it makes no difference if you use common rows or common columns.
For example we take common rows and independent column drivers. 8x8x15mA = about 1A (per 8×8 display)
Let's connect the rows to the anodes and the columns to the cathodes of the display. 8x15mA per column

I recommend to select the rows to use a HC138 and as drivers: 8 logic level P channel MOSFETS.
Even SOT23 sized can drive 8 pieces of 8x8 displays.R_ds_on < 0.15 Ohms for driving one display. < 20mOhms for driving 8 displays
Connect all 8 Mosfet sources to VCC, each drain to row, and each gate to the 138 outputs.

The HC138 has inputs A, B, C to select the rows, and you need an enable pin to avoid ghosting.

And you need a low side driver for each column. It needs to drive 8 x 15mA = 120mA. R_ds_on < 1Ohm,

Sequence:
* disable all rows ( to avoid ghosting)
* update all columns (for row x)
* enable row x
* delay 2ms
--> restart sequence with next row

Remember to disable all rows every time you can't run the seqence (at power up, when busy with other things, during reset)
to avoid that the LEDs burn caused by the increased current.

Klaus