Hello everyone. I'll try to keep this detailed yet brief. And seriously, THANK YOU in advance for any help. I love the open source community and it's the only reason I can do the things I love.
I am working on some home automation using ATMega328P-PU chips (bit overkill but the ATTiny85 is short one or two pins for my NRF24L01 SPI along with sensors)
So, here is the setup:
I have a central control hub powered over AC with a battery backup. Then scattered around the house I will have little 'boxes' with an atmega/relay/nrf24l01 to turn AC plugs on/off wirelessly. The hub also transmits wirelessly to my Ethernet connected client that updates my webserver (on a paid hosting site).**
This system is already mostly in place other than the relays and is fully functional because its actually a security system I've been working on. It uses some fun laser trips, PIR, door sensors, etc. The coding is not my issue. Over the last few months I have successfully gotten my security system up and running and can control it over the internet and with SMS and all that jazz. TFT screen, touch keypad entry, nice looking enclosures for PIR sensors on ceiling using 120VAC all the fun stuff)
And here is the problem:
I am adding the "home automation" piece now and am not sure what would be the best way to power the wireless relay boxes. I know how to get some 12VAC power down to 5VDC (all my motion sensors are doing this using old phone chargers as we speak) but then what happens when I decide to say "Turn the device off"? For example I use my web server to say "Turn plug 5 off (a lamp)". What would be the best way to wire this so that the relay/microcontroller/nrf24l01 still gets power from 120VAC but the device no longer receives power? Obviously the control box needs power to turn the dang light back on when I ask it to. Is there a best/safest way to do this?
As far as design, I have been thinking that I will make a little enclosure with the relay/atmega/nrf24l01 inside and it will have an outlet in it and a plug also coming out. If I want to control a lamp wirelessly, I'll just plug the lamp into my little box that I've made and plug the box into the wall. This way I can move them to any device. I also never felt safe sticking this stuff INSIDE the wall because I just bought this brand new house and would hate to burn it down.
I haven't given TOO much thought to this one part yet (the power to the box), but I wanted to get some opinions before I went too far down the wrong/dangerous path. How do I get the AC power into my AC/DC converter/buck module while also turning off the 'lamp'. Should I use two relays and have one as Normally Closed and suck some power out of that and then have the second relay in series with that, but controlled with the atmega? There are a few little things that come to mind but please help so I don't do something stupid.
Disclaimer (not related to question really):
I am not an electrician, just a hobbyist in electronics and programming. I do all my own stuff and am 'self taught' (by people like you!). I always write all my code from scratch. I never copy other's stuff (although I will use libraries which is in a way copying but whatever). I just do this for fun (its an obsession really) so I don't have any formal training. I have no college whatsoever actually. I am, however, an unusually paranoid/careful person. I am also ironically scared to death of electricity. That being said, I am extremely careful with high voltages. I take 10 times the safety precautions than are probably necessary, but I would rather do that then get shocked. As a funny side note, the only thing that got me into electronics to begin with was my fear of electricity. I thought that my intense fear of electricity would be somewhat lessened by a little education on the subject. This is what the result was. I am now obsessed with electronics.