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
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)?
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:
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.
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.