IMHO this product deserves to be better known. I’d hate to have it disappear, it’s a great boon for electronic hobbyists in general, in safety and convenience.
EVERYBODY has something that runs on household AC that they’ve thought of controlling programmatically. Electronics hobbyists, tinkerers, programmers are thinking of stuff all the time. You have an Arduino or a Raspberry Pi, you can control some pins, now how to use that to turn whatever-it-is on and off?
Usually this has been done with relay boards, or maybe solid-state relays, but there are real downsides. For one thing, you’re fooling with “mains” or “house” current, nominally 120v AC. I’ve done it often, but it so happens that I worked with 120v current professionally every working day for a lot of years, a long time ago. It’s not something I’d ever advise anyone to experiment with without close and qualified supervision.
The other problems have to do with controlling relay boars, or solid-state relays. There’s usually no big hassle there with an Arduino or compatible controller, they usually (but not always) use 5v DC for the logic and I/O. Not so with the Raspberry Pi, though, it uses 3v DC, and very few of the common inexpensive imported relay boards are set up for that. You can use discrete transistors, or a level shifter, either a chip or module, it will work.. you still might want to isolate it optically for safety, yet another step.
Then, since it’s 120v you’re fooling with, you REALLY want a decent and safe enclosure for it, you can’t just leave it hanging out there.
Now it’s easier easier, safer and cheaper, especially for people without that experience. This is relatively new:
or:
This is about half the price any similar product I’m aware of (actually I’m only aware of one, the “Power Tail”), and a whole lot more versatile- control voltage can be anything from 3.3v to 60v DC, or 12-120v AC, so you can control it directly from RPis, Arduinos, even house current without level-shifting or an inverter or whatever. Two NO outlets and two NC outlets. Optical isolation, anti-bounce (the simple relays are famous for wiping router memories) and over-voltage protection. Ladyada did a tear-down and pronounced it good, Adafruit is investigating carrying them. This has got to be the easiest, cheapest and probably safest way to control AC from a Pi right now.
The same outfit that makes this also has a $9 add-on (sorta) box that controls a relay from a typical AC plug, which I find a little bewildering, but maybe I just lack imagination. I guess you can control AC from low-voltage DC and use that to control DC again? Not sure.
– Robert the Wombat