I’m supplying 9v through a 5v regulator. This regulator powers five IC quad gates. This is all for a 4 bit ripple carry adder.
With that aside, could I just power the LEDs (which will visualize the 4 Sums and the last Carry) with the 5V, connecting GND to an LED to a Sum output on the IC, for example? I think that's what this guy (Ben Eater) did in this video:
I'm really novice to electronics so this question may sound silly to the more experienced.
Best Answer
Some logic chips have definite current limits built into their output structure, but many do not. Depending on the logic chips being used you may well be able to direct connect the LEDs from output to ground, but I'd suggest you should not.
The forward voltage rating of your Green LEDs depends on the silicon elements and dopants used, but is likely somewhere from 2.2 to 3.3 V when conducting.
This might help you for the various LED colors:
What I would suggest is that you should connect your LED with a 1K Ohm resistor directly to +5V and ground. This will allow you to measure the forward voltage (even if it's not very bright) across the LED. From this voltage you can then calculate a series resistor to suit your application and set the LED maximum current.