I'm building a Pi3/Retropie based emulation box specifically for computer based emulators (Spectrum, C64, Atari ST etc).
It's 90% complete, but I have a few loose ends to tie up.
I've hooked up a power LED, but I cheated and connected it to the power supply, so it's on whenever the power supply is on, whether or not the Pi itself is powered up.
What I'd like to do is have a second LED for activity, mostly so that I know when it's safe to switch off the power.
I have found some guides online for connecting an LED to the GPIO pins.
These look simple enough, but appear to be mostly for older Pi models or for the Zero.
A few of the more recent guides cryptically mention that they won't work for the Pi3 because 'something changed', but don't go into any detail.
Can this still be done on the Pi3, and if so, how?
I already have the LED and resistor ready to go, I just need to know which pins to connect it to and any accompanying code needed.
I would prefer processor activity, but SD card activity would also be ok.