I followed the instruction of using Arduino Nano as the power supply, but the LED didn’t light up. There are two problems that I did not realize until a day later:

1. I connect the usb from the Arduino directly to my computer. Somehow there might be connection problems and the Arduino did not receive power from the computer (the light on Arduino didn’t light up.)
2. I did not realize that the top and bottom halves of the breadboard is not electrically connected (as there is a gap in the middle.)
3. MOST IMPORTANTLY: the positions of the wires are completely messed up (the third photo), because I did not understand the circuit/schematic diagrams at all at that time… The black wire (ground) on the top left should be pinned in the negative polarity column. The ground side of the resistor should be pinned in the negative polarity column as well.

    The next day I found a AC adaptor that has the output of 5V and I connect it to the Arduino Nano – the light on the chip lit up!

    I fixed the problem of mispositioning the wire, the LED still didn’t light up… After asking a friend, I realized that this breadboard is split in the middle and the top and bottom halves are not electronically connected. I moved all the components to the top half and the LED finally light uppppppppp!!!!!!

Question: What is the purpose of the bottom black wire? It seems like an extra wire in the circuit, considering the schematic diagram. I unplugged that wire and the LED was still lit up.

Voltage measuring:

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