3 way Dimmer switch?
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This past weekend I tried the three-way switch conversion suggested by @KazaUser. Except instead of what I believe @KazaUser did which is to put in a single pole (HS200) in as a dummy/unloaded/control switch, I put in another dimmer (HS220) as the dummy switch, to mixed success. My goal is to have a dimming control that works correctly from both switch locations.
TL:DR - Because the Kasa app only allows the on/off switch (and not the dimmer buttons) to act as a trigger for an action (within the Kasa App), and you can't remotely change dimming levels in the HS220, you can't control the dimming functionality of the loaded dimmer from the dummy dimmer. You can use this configuration to turn on/off the light fixture.
Here is a diagram of how I wired things:
In the switch box that had the mains line I wired one of the two traveler wires (black or red, I chose black) permanently to the line and I capped off the other traveler wire (red) with a small wire nut. I also wired a first HS220 in the box connected to the line voltage, but without anything connected to the load terminal. So that first HS220 was acting a dummy controller. In the other box, I wired the black traveler (now at line voltage) to the line terminal on a second HS220. The lamp load was then connected to the load terminal on that second HS220. So the second HS220 acts as a normal single pole dimmer.
Then I set up a Smart Action in the Kasa app. The trigger device is the first HS220 and the corresponding device is the second HS220. With this Smart Action, hitting the on/off switch on the first HS220 will trigger the second HS220 (that controls the lamp) to turn on and off. As @KazaUser mentioned, there can be a little lag in the response, but it was generally acceptable.
Having acheived correct on/off functionality, I then turned to trying to figure out how to get the control of the dimmer to work from the first HS220 to the second HS220. I wasn't able to figure that out. The Smart Action configuration appears to have two shortcomings:
A) The only triggering action from the HS220 that is available is the on/off. Neither the dimmer control buttons, nor long/double press are actions available as a trigger.
B) The actions available for the HS220 as the corresponding device are only on/off. There is no ability to specify an action to change the dimming level or to trigger a scene or preset.
A feature request to TP-LINK would be to support setting up more complex triggering actions or as a simpler alternative, to allow devices within a group to control each other.
For what it's worth, I did a little reading to see if it would be possible to set up an IFTTT recipe for the behavior I'm trying to get here. From what I have read, TP-LINK/Kasa does not support the HS2xx line of switches as triggering devices with IFTTT, so I stopped there. I'm also not sure if IFTTT can set dimming levels if you had a different triggering device.
I welcome any feedback or suggestions for ways to improve this configuration. I note that this does match the functionality of a traditional three-way dimmer circuit where one switch location is only on/off. This does not match the functionality of newer three-way dimmers, like from Lutron, which provide for a "companion" dimmer that uses the traveler wire as a signal to send dimming commands between the two (or more) switch locations and thus allow for dimming control from both locations.
