I have the above circuit connected to my computer. The Pro Micro is running the following program (code HERE):
Check if computer is on or off by verifying if the motherboard LED+ pin is HIGH or LOW, respectively (pin 5)
If the computer is off, check the input from the fingerprint sensor;
If the fingerprint is valid, turn on the computer by setting pin 4 HIGH which in turn switches the transistor and then sets it LOW after a small delay -- mimics a power button press.
As long as the Pro Micro is powered, the setup works with no issues. But when I unplug the Pro Micro, the computer shuts down and I don't understand why. And it's not momentary like a button press. It's like the transistor is on fully, resulting in a long button press.
Can anyone help me understand why this is happening when unplugging the Pro Micro?