It is basically SMS based arduino controlled relays with google assistant setup to send messages on voice instruction .It is very easy and cheap and works like Alexa advertisements with your existing electrical appliances (if you have Moto -X smartphone it can work even better than alexa)

it is a little slow as it is SMS based but works flawlessly and can be controlled from anywhere(check video)

There are 3 basic steps

1.) setup and programm the hardware

2.)setup google assistant

3.)connecting to appliances

You can extend this to every switchboard of the house by using RF trans-reciever(will cover this in next instructable)

videocompress-026-VID_20190712_173443.mp4
Download

Step 1: Setup and Programme Hardware

Components needed

1.)Arduino UNO

2.)Sim 900a GSM module

3.)one active full size Sim card (GSM module sim tray is for full size sim Card)

4.)Power Supply 12 v 2Amp adapter

5.)Relay board(12V 10A)

6.)Male to female wires (to connect from arduino uno to Sim 900a and relay board)

Give 12 V 2A supply to SIM 900a board and to relay board for arduino sim 900a can supply

connection as per diagram

Sketch as uploaded Edit your mobile number in the sketch

Sim900a_Sketch.ino
Download

Step 2: Points to Be Noted

Sim 900a GSM Module bit rate that works for me is 38400

Some sim require more current to get signal (so use 2A power supply to avoid restarts)

Note* i have used telenor sim at first but it is requiring more power and sim 900A module getting restart every 30-40Sec then i have used BSNL sim and it worked smoothly with no restarts at all

I have already made a internet controlled home automation long back but now i have posted in an area where there is no LAN or wifi connection thats why i have switched to SMS controlled home automation and its benefit is it can be easily integrated with google assistant

Step 3: Setup Google Assistant

Open Settings->Google Assistant->Assisstant tab->Routine

the add coustom routine by touching Blue Color Plus button at the bottom right

then add command like "Light on" etc

the add action to this routine -> choose popular action->Select send text and say something and touch ADD at top right

after adding and saving come back to routine window (5th image) then click setting button in front of send text

Add number of the sim which you have put in SIM 900a module and write the text you want to send (must be exactly same as in sketch)

in say something you can add anything you want google to say after doing a work like "turning on the light" etc

add all the voice command seperately ( Light on,light off,fan on, fan off etc) as above

check screenshots for any confusion

Step 4: Connecting to Switch Board

Connect the relay to the switches in parallel only (because if there is any problem in the signal of sim or in arduino you can still turn on and off the lights in good old fashion)

common to 220v supply (Bottom terminal of switch)

NO to the equipment(top terminal of switch)