Hello all and Merry Christmas.  I am checking in to report on a project to remote control the wreaths on my front door.  The Internet doesn't know how to do this, but after a bit of trial-and-error now I do, and so I am adding to the knowledge base :)

All over my house I have stuff which is controlled remotely lights, plugs, switches, you name it.  Everything has a little app, every app has an Alexa skill, and so I can use Alexa as my home automation system.  Works great.  (Under the covers each of these little devices is using WiFi to connect to a cloud server, and the Alexa skill links the device's cloud servers to Amazon's cloud servers...)  At Christmas I add to the device count with lights on the roof, an inflatable gnome, candy canes along the drive, etc.  All WiFi controlled, all connected to Alexa.  At dusk everything comes on automatically, and at midnight everything turns off.  Life is good.

On my front doors I have a couple of nice wreaths, and they are intertwined with strings of little lights.  The lights are battery powered, each driven from a pack of 3 AA batteries.  There's a small switch to turn them on and off.  But who wants to do that?  Too easy!  Of course these lights should be connected to Alexa too...  Therein lies the problem, the tale, and the solution.

My first attempt was to find "battery powered WiFi switches".  After a bit they were indeed found.  These switches are designed to be fed DC power, which enables the WiFi connection, and which is then conditionally relayed to a device.  Unfortunately after a bit of experimentation it turns out 3 AA batteries don't provide enough voltage for the devices to operate.  They need at least 5V (the voltage of USB) and 3 AA provide 4.5V.  So close.

Okay what to do?  Well, let's get a battery pack with more voltage!  And so this was done.  These packs have 6 AA batteries for 9V, and sure enough the WiFi switches worked nicely.  But ... the light string is designed for 4.5V, not 9V, and the little lights would not illuminate.

So now what to do?  Well, let's get a voltage regulator!  And so this was done.  These little circuits take any DC voltage in and deliver a lower DC voltage out, configurable via a tiny screw.  Going from 9V to 4.5V worked.  So now we have a 6 AA battery back (9V) connected to a WiFi switch (9V) connected to a voltage regulator (9V -> 4.5V) connected to the light string (4.5V).  And sure enough, this worked!  Yay.

But if that was the end of the story it wouldn't be as good.  So here's what happened.  It turns out WiFi requires a lot of power.  A WiFi radio is not only a receiver, but a transmitter, and it has to be on all the time to stay connected to a network.  (Even during the day when the lights are off.)  And so the 6 AA batteries only lasted a few hours.  Yeah, they are rechargable, but swapping batteries all the time is much worse than flipping a small on/off switch and defeats the whole purpose.

So now what to do?  Well, clearly WiFi is not the answer, or at least, not the whole answer.  The right remote control tech for this kind of application is a radio controlled (RF) switch.  Send a signal, and the switch switches on, send it again, it switches off.  The battery powered side only needs to be a receiver... much lower power, much simpler.  I need RF switches.  So this was done.  And so now I have two DC transmitters and two DC receivers.  On each wreath I connect the batteries to the receiver to the lights, and somewhere else in the house I connect the transmitter to... what?  Well, I need a WiFi switch again!

So I found a different WiFi switch, with two channels.  This is designed to be powered from USB.  And this I did; in my office I have a USB power cube (5V) connected to the WiFi switch (5V) connected to the two RF transmitters (also 5V), one on each channel.  I connect the WiFi switch to the network, tell it to turn on, the transmitters send a signal to the wreaths.  Everything is happy and this works!  Um, no it doesn't.  The lights on the wreaths come on but then go off and blink and generally act unhappy.

After a bit of futzing with a voltage meter, it turns out the original 3 AA battery pack was fine for the lights alone, but the voltage drop with the RF receiver caused the lights to flicker.  Actually there was a weird cycle; the "on" signal was sent, the lights would come on, the voltage would drop a bit, the receiver would disconnect, the lights would go off, the voltage would come back up, the receiver would reconnect, the lights would come back on, etc.  Not good.

So now what?  Oh wait, I have the 6 AA battery packs!  And the voltage regulators!  So on each wreath I configured the 6 AA pack (9V) to the RF receiver (9V) to the voltage regulator (9V -> 4.5V) to the lights (4.5V).  And yay, this works!

In my office: USB -> WiFi switch -> RF transmitters

On the wreaths: 6 AA pack -> RF receiver -> voltage regulator -> lights

It works, and not only that it keeps working, because the RF receiver doesn't draw a lot of power.  Merry Christmas!