Using SSR relays in varying circuit is common with micro controller. What if the micro controller failed for a while? we will not be able to control our device manually. This approach will do by adding a mechanism that mimic our home stair-case switch with our controlling point running independently.

So let's make it.

Step 1: Finding an Electronic Switch to Serve the Physical Switches

Making a google search for SPDT chip, you can see quite many products, I finally chose sn74lvc1g3157 as it cheap and can be found on Shopee easily

Looking at datasheet, I make a small schematic using two sn74lvc1g3157 to mimic the two way stair case switches

https://www.ti.com/lit/ds/symlink/sn74lvc1g3157.pd...

Please diagram

So IO1, IO2 are controller pin from micro controller and the touch button (TTTP223).

Step 2: Make a Simple Relay

SSR relay with triac and opto-coupler is also common, I choose BTA16-600B as it can run up 16A at peak and 240W (~1A) at normal state without heasink, more than enough for a normal bulb, small fan or even to drive magnetic-relays to control much larger loads.

Full schematic is provided here https://easyeda.com/editor#id=|a714ab25f7b24a48bc...

I tested the with ESP8266 and Arduino with I/O range from 3-6VDC, load (resitive - 300W, inductive - 180W fan, capacitive - 2 laptop adapters).

The genuine ST triac can drive large capacitive load but the cheap Chinese BTA16-600B triac (see picture) will die when loading 02 laptop adapters, so - let's be noticed. BTA16 is said to be snubless so I remove RC snubber in my actual application and tested them successfully (both the genuine and the cheap chinese triac)!

Step 3: Make a Pcb or Solder One on Your Owned

I decided to solder one test PCB first and run with ESP8266 before placing order to PCB maker. It seems all run well over a month with my soldered board and now I make 10 of real PCB with separated relay and controller so it can be easily expanded.

Easy huh. with all I made, total price is about 1.5 USD for one relay (Including PCB), so with a controller (ESP8266), we can control our home switch easily and safely