5x5 LED Matrix - Using 74HC595B1

Hello All,

I was planning to make a 8x8 LED matrix using 74HC595B1 ic but after looking at the datasheet Ive realized that with a maximum current output of 70ma that would not be happening.

being lazy and the fact i can do with a 5x5 as well, my question is if i design the matrix assuming only 1 row can be lit up at any given time ( 5 leds active at any time => individual pin current of 70/5 = 14ma) can this be done.

was planning to arrange the matrix in common cathode config with row and col selectors and using the appropriate current limiting resistors for the led.

worst comes to worst the leds would be a bit 'under-lit' .. am i correct ?

thanks for the help, ankit !

If you get 8 NPN transistors, you can light as many LED’s as the transistor can handle while only using a few mA from your IC. Or you could do a 8x5 matrix if you want

ok … so as a test i wired up a led matrix as per the schematic attached. now when i attach +5v to point C and GND
to point B (as column/row selector) the led does not light up :(. but when i attach +5v to point A to make sure
the led is not burnt out, it lights up.

can anyone help me figure out whats going wrong here ?

thanks
Ankit

Untitled.png

Might be bad resistors, or maybe they're too high a value(are you sure they're 330?). Might help to post a pic of the actual matrix

I would not care simply wire the LEDs.
Look inside your computer hard drive gets very hot,
if your 74hc595 become hot like this, you need to start worrying.

It would be nice some day people stop using transistors, resistors for these circuits,
these are superfluous components.

If you use low voltage 2.4 or 3 volts you can’t really have transistors/resistors anyway,
or you don’t get much brightness.

74HC logic ICs have built-in equivalent resistance of 120 Ohms.

  • LED internal resistance
  • sink resistance
  • power supply internal resistance