Step 5: The cathode multiplexer
Required parts:
Placing the parts:
2*74HC595
shift registers
2*100 nF
16*6,8 Ohm
or short links
Make sure to line up the notch on the 74HC595 shift registers with the mark on the board.
Here you have another tough decision. Many hobbyists drive their matrix without resistors. At first this seems odd. We all know that LEDs need resistors.
However, the Darlington arrays have resistors so these may be enough and there have yet to be reports of LEDs burning out. Especially, since the silver
wires that connect the LEDs in the matrix are good heat conductors and good heat removal is essential to the long life of LEDs. So thrill seekers can
replace the resistors with wires or jumpers. Those who want to be sure can add the resistors from the kit. These are small, only 6.8 ohm.
Those who set the jumper to „Vext“ must adjust the values of these resistors as previously discussed.