How to connect a button (via GPIO) to a K16A-B

[k6ccc]

For me, its best to go with a driver transistor. 

Agree 100% with that low of current capability on the GPIO pins.

[pierlux]

Alright I brushed up on the suggested transistors using this great write up but really, are these easy to use modules really that bad? 

[pck]

I'm sure the relay module will work. If its more convenient for you to wire up than soldering, its a way to go. Its just overkill. The module uses a transistor to turn on the relay which then powers your led. A single cheap tiny 2N2222 can power the relay directly, no relay middleman. 

[k6ccc]

Agree with pck - that module is MASSIVE overkill.  I think his last sentence had a brain thought run together.  Should have read " 2N2222 can power the LED directly, no relay middleman".

One 2N2222 transistor, two resistors and the LED.

[pierlux]

The module is nice for the software engineer in me: plug-n-play. No resistor to compute.  I probably could get the transistor and resistor working but I'm trying to keep it simple.

Now, for the last bit of complexity: in my 3 wire setup illustrated above, is it alright if I have a 3.3V wire, and a 12V wire sharing the same ground? The 3.3V is for the button GPIO, and the 12V will be coming from the relay module.

I think it'll be alright (I don't want 12V to feed back into the GPIO) because the LED acts as a diode (allowing current to only flow in one direction).

[k6ccc]

Yes, all the grounds should be tied together.

[MikeKrebs]

On the 3.3/12V ground sharing question. If the 12V is on the output of relay, it doesn't matter. The keep it simple part in me says run the 3.3v/ground for the button and run 12v/ground for the LED.

If you were talking about a controller and pixels where we were concerned about having a common understanding of ground, then they would get grounded together.

[k6ccc]

On the 3.3/12V ground sharing question. If the 12V is on the output of relay, it doesn't matter. The keep it simple part in me says run the 3.3v/ground for the button and run 12v/ground for the LED.

If you were talking about a controller and pixels where we were concerned about having a common understanding of ground, then they would get grounded together.

You are correct in this specific situation.