i noticed that some circuits instead od connecting to a gpio pin and ground ...

1502093546

was going through the manual and i noticed that some circuits instead od connecting to a gpio pin and ground it connects to gpio pin and then either 3.3 volt pin or 5 v could please explain why

Adeept

This is actually a question of programming or circuit design logic. I believe that the picture I provided can explain this problem.
See the attached picture.

Adeept

In the circuit, the current always flows from the high potential side to the low potential.
In the circuit we provided, the anode of the LED is connected to the power supply (High - 3.3V), and the negative pole of the LED is connected to the GPIO of the Raspberry Pi. When we program the GPIO output low level (0V), the circuit is turned on, the current flows from the high level (3.3V) to the GPIO, and the LED ON; when the GPIO output is high, the voltage between the positive and negative of LED is the same, no current flows in the LED, so the LED is OFF.