Electrical Components in Checked In luggage

Checked baggage goes through security screening, the same as your hand luggage does. The only difference is that your checked bags are checked without you being present, so no chance to explain what they are seeing on the screen.

How the security folks would deal with a checked suitcase containing something that perhaps resembles an explosive trigger is anyone's guess. They might try to open it, they might simply destroy it. If they can't determine what it is, they will come get you for further questioning.

You might be better off carrying it onboard, as at least you will be there to explain what it is when security discovers it.

In my experience, there is absolutely no problem whatsoever with this sort of thing. Bare populated circuit boards are easy for the x-ray folks to inspect, in fact they will look similar to familiar packaged electronics since the case is generally almost invisible to X-rays. I quite often travel with this sort of thing (prototoypes, evaluation boards and so on) and have encountered zero problems, not even any evidence they looked into the bag. They can see there is no danger.

Do not put batteries in checked baggage especially in home-made electronics, and never lithium cells. I'd also be a bit careful about weird looking bare or home-made looking electronics in carry-on, just because it might freak out another passenger if they happen to see it (perhaps whilst you are accessing your in-flight cache of snacks) which you do not want to do.

The only thing worse would be to pull out your Arduino with flashing LEDs and start plugging it into your laptop to get a bit of programming done in-flight.