This is my first foray into Raspberry Pi (and these kinds of electronics in general) as well as asking questions about it here.
My goal: Attaching a power indicator LED along with a fan (Pimoroni Fan SHIM). For some reason I can't get them working at the same time.
Details: I'm trying to add a simple external power indicator LED that turns on and off with the system. I used the guide found here to wire my LED to the TXD pin (pin 8) and GND (pin 20 because both 6 and 14 are already occupied by other wires). My circuit is as in the guide: TXD -> LED anode -> cathode -> 220ohm resistor -> GND. I'd include the specs of my LED, but I'm not sure what they are... It came with the resistor as a set though, so I imagine they must be appropriate for each other.
Other devices I have installed are a Pimoroni Fan SHIM (here is its pin layout) and a NO momentary switch to turn on/off the system by shorting pins 5 and 6. For the fan, I have a pull-down resistor installed between GPIO18 and GND (pin 14) so that it stays off when the system is off. Both components work as they should.
The whole setup works nearly as intended and the LED lights up fully when the system is on, but it remains half-on when the system is off. I have to unplug the power to turn it off completely. I included pictures at the end for comparison.
According to the guide and as noted by other sources/forum posts/comments I've read, using the TXD pin should be straightforward and work with no real programming. In the end, I was able to get the LED to work perfectly by removing the Fan SHIM entirely. Now I'm suspecting that the fact it uses the very same TXD pin is interfering somehow.
The answer to this post makes it sound like this kind of shared GPIO shouldn't be an issue, but if removing the fan fixes the problem, I'm not sure what else to think. Though the fan is provided with scripts to run fan curves and operate the built-in LED and tactile switch, I haven't installed any of these and I simply turn the fan on at boot with
dtoverlay=gpio-fan,gpiopin=18,temp=20000 in config.txt and let its pull-down resistor do the rest.
My question: Is there a way to get this all working while keeping the fan installed, or can I really only use either the LED or the fan, but not both?
Apologies if there's a lot of information in this post. It feels like it's probably a simple problem, but I'm at my wits' end now. Thanks for reading.
Some final stuff if it helps at all:
- Raspberry Pi 4B, 4GB
- Official power and HDMI cables
- RetroPie 4.6
EDIT: Just out of curiosity, I tried wiring up an LED straight to the Pi's first 3.3V pin, and it's lighting up the exact same way it does in my second picture below; a faint point in the middle that persists as long as the Pi is plugged in, on or off. Does that mean anything useful?
Here are those pictures of the LED and the whole circuit: