TP-LINK HS200 is a very nice product. It's cheap ($39), directly connects to wifi without any additional hub, the Kasa App is great and works with Amazon Alexa.
But sometimes you want to keep that three-way old school switch, and HS200 doesn't support this kind of installation. Now you can do it!
This instructable requires soldering know how and electrical installations. It's easy and cheap, but if you are not familiar with both, please do not proceed.
Just to remember, your HS200 warranty will be void :) Do at your own risk.
Step 1: Open the Unit
First step: Open the unit. There`s locks at the sides of the switch. Gently force the plastic and you`ll open it.
Step 2: Remove Green Wire, or Create Another Hole
For this modification you will need a hole to pass a pair of wires.
My installation doesn`t have the ground, so I removed the green wire, it`s only attached to a metal plate that makes contact with the switch housing in the wall (my housings are plastic, so it doesn`t make sense at all ;) )
Step 3: Prepare Electronic Parts
Well... you know how to use a soldering iron, right?
Here's all the parts that you need:
1x Optocoupler 4N25
1x 100uF x 16V (or 25V) electrolytic capacitor
1x 47KOhms 1/8W resistor (FOR 120V) or 100KOhms 1/8W (for 220V)
1x diode 1N4004 or 1N4007
You can spread the terminals of 4N25 optocoupler. Pay attention at the pin 1 indicator.
Step 4: Put All Together
Using your manual ability and a soldering iron, put all together following the schematic.
You can do it in any other way, but the second picture is my suggestion.
(please note that the capacitor on the second picture is 10uF, it's wrong! The correct is 100uF, otherwise you will have a lot of bounce with the new switch)
Step 5: Connect New Wires to HS200
Now pass white and blue wire of your circuit thru the housing hole.
Following the picture, connect blue and white wires of your circuit to HS200 control board.
Blue wire will connect to ground, and white will connect to main switch.
Step 6: Close the Unit and Finish All External Connections
Now you can close the unit.
Connect the diode terminal to the original HS200 white wire (neutral)
Then, carefully isolate every terminal independently, avoiding any short circuit.
You will end up with a new RED wire to use :)
Step 7: Connect Your Unit
The schematics show how your three-way circuit should look, and how you will connect your new hacked HS200.
HS200 will be connected as usual. But the red wire should be connected to the old three-way second wire.
At the other side, the first old three-way wire should be directly connected to phase, and you need to replace the standard switch to a pulsating one, connected as the schematics shows.
VERY IMPORTANT: The pulsating switch MUST BE at the side where you have the PHASE, and HS200 where you have the returning wire to the lamp.
Turn off energy BEFORE INSTALL