(This is based on an idea by Ard Jonker, who planted a seed and watched the coin drop, if you excuse the mixed metaphors…)
The recent experiment with direct relay switching suggests that it is possible to switch a latching relay with just two I/O pins tied together plus a 100 µF cap.
The thing about that circuit, is that it draws no current in either ON or OFF state – it only needs a little energy to change the state.
That means it could in principle be powered by a very low-power source, such as this other fun projects I had to shelve a while back. The reasons for this remain as valid as ever: I can’t realistically turn this into a safe kit, given the direct connection to AC mains. So while the thought of having 80 of these sprinkled around the house and consuming under 1 Watt total is a tempting thought, it just isn’t going to happen.
Which doesn’t prevent ME from using it anyway, of course…
Ok, now let’s bring a couple of components together:
- a JeeNode Micro
- a 12 mW AC mains supply
- a directly-powered latching relay
- a toggle switch
- power cabling
Here they are, with a nice plastic case (whoops, forgot to include the JNµ, oh well):
The toggle switch is the small but essential ingredient here. Let me explain:
This is a switch which can be operated manually and remotely. Flipping the switch or the relay has the same effect: toggling power, regardless of the state of the other component!
This means it can be operated even when the automated system is off or disconnected, or has crashed. And likewise, the power remains under remote control regardless of the state of the manual toggle switch. This solves a key problem with all those cheap remote power switches out there: the necessity to find the remote, because there is no local switch anymore. And the fact that it breaks down when the home automation system fails.
Given the relay used, I doubt that this solution will be able to control more than 30..50 W, but there are plenty of such devices around the house these days, even LED lighting.
I think I’m gonna have to start messing with AC mains again… with caution, of course.