I am building an LED matrix using flip-flops. I will have 128 rows in the matrix, so I am using 16 octal flip-flops, where all inputs to are shared and come from a microcontroller, which uses 5V logic.
I would like to supply 3.3V to the latches so I don't need to solder 128 resistors for each LED (forward voltage of my white LEDs is 3.3V). I tried doing this and the latch stopped working, producing unpredictable results. This was a bit of surprise as the flip-flop is documented to work within a range that includes these two voltages. I presumed that the flip flop didn't like two different voltages coming into it.
With my very limited electronics knowledge, I thought the following would work:
It seems to work fine. However, I have since come across this question:
Where it states that as long as you limit the current going in, no permanent damage will be done. So I tried removing the transistor and just placed R1 between the microcontroller and the flip-flop. It worked.
I have a feeling my circuit above either massive overkill and/or wrong in the first place. Is just using a resistor OK? Any pointers/corrections would be gratefully received.
For reference the flip flop I am using is a SN54HC574