How to calculate Resistor value for LED Matrix

Hi Everyone,

I'm building an LED matrix 24 rows by 108 columns.

I know i need resistor in each colunms, and each rows.

I'm trying to figure out how to calculate the resistance for the columns and the rows.
could someone help figure the resistances values for each
columns and row? plz

source voltage : 5.28 v
Led : 2.2 V
LED mA :20

I have 100 ohms connected with each columns
and

1k ohms with transistors connected with each rows

is it correct?

It depends how the transistors and resistors are connected, and the forward working voltage of the LEDs. Also what device is driving the rows?

shift register for the columns

and

decade counter for the rows

jafleu:
shift register for the columns

and

decade counter for the rows

I meant, what logic family? Also, how are the transistors connected? What kind of transistor? Have you bench tested the circuit to see how it performs with the values you have selected (one transistor, one LED)?

source voltage : 5.28 v
Led : 2.2 V
LED mA :20

Let Vcc = source voltage : 5.28 v
Let Vf=Led : 2.2 V
Let If=LED mA :20
Rcurrent limiting = (Vcc-Vf)/If=(5.28V-2.2V)/0.020A=154 ohms

You only need 1 resistor, either for each row, or for each column.
Resistor choice will be determined by Vf of LEDs, voltage drop across the common anode or cathode transistor, whether you are multiplexing fast enough that you can support higher pulse currents (check your LED spec, often can have a higher current pulse for short period of time, example:

Peak Forward Current (1/10th duty cycle, 0.1ms pulse width): 50mA
https://www.superbrightleds.com/moreinfo/through-hole/5mm-red-led-30-degree-viewing-angle-8000-mcd/281/1208/ (scroll down ~ 1/2 way)
vs 20mA continuous.

Individual current sinks are easier to create than current sources.
TPIC6B595 high current shift register can sink 8 50mA loads easily, with a P-channel MOSFET providing the 400mA for the common anode. 2nd TPIC6B595 can be used to sink P-channel Gate to turn each one on individually as well: setup the cathodes, turn on an anode, wait 100uS, turn off anode, setup next set of cathodes, turn on next anode, etc., repeating for all 8 columns.

In your picture you have resistors in the rows and columns .
should the have the same values

Could be - depends on the transistors you use.
(5V - 2.2V)/.02A = 140 ohm,
so you could use 150 ohm for current limit resistors
And for transistor base (or gate) current limit resistors also.

its a 2N3904 NPN

so 140 will suffice both rows and columns

so 140 will suffice both rows and columns

You don't need them in both as CrossRoads told you. Just in one.

But it depends on how you are driving the matrix in software as to which you need.