Control Basics
Warning
This is a fast moving field. This information will be out of date in some detail even before you read it.

OK to me home automation involves controlling stuff. I want smart switches turning things on and off because I say so or because the system realises that that is what I want.

When I started I already had various lumps of hardware starting with a cheap set of plug-with-a-socket-built-in that were controlled by a handset bought as a set from the local Asda supermarket and then more complicated things such as a set of motorised curtains. I also had an Amazon Alexa that could connect to and control various other devices I had purchased. However I had found the use of the cloud frustrating. Alexa was OK, running on Amazon's global server farm probably makes her more resilient than NORAD, but several of the systems I used only seemed to be up for most of the time. The whole idea of going to a homeassistant based system was to only use the cloud for real cloud things but not to send my request to turn on my desk lamp round the world and back to action it.

I have divided switches and things into two groups. Stuff I can control directly on the Wi-Fi including things I can modify to do this and the stuff I already owned where I have to emulate the controller.

Before I go any further a short few words on the difference between the two. The hand held controllers are like your TV remote. They have a 'fire and forget' attitude to their control signals. You push the button and it is sent off into the void either on infrared (IR) or radio (RF) and the controller's job is now done, it neither knows nor cares if its message has been received and if it isn't you just push the button again. This 'not getting through' problem is hardly significant to an experienced button presser but to an automation system is a serious problem. Incidentally the 'not getting through' problem seems to be more prevalent for the RF devices so their longer range, eg room to room, comes at a cost.

A Wi-Fi based system however is very different. The message is sent via the router on protocols that specifically require a reply to confirm that the message was not corrupted or lost for every step of the journey and the number of end-to-end fails is very very small. This is highly suitable for automation systems so I am trying to move everything on my own system that isn't irretrievably 'built that way' onto Wi-Fi.

For emulation however I have had good results using the Broadlink range of senders especially for IR, more of that in a moment, but for direct control flashing new code into smart devices with 8266 controllers has worked very well. The picture on the right are some flashed Sonoff 'Dual' boxes wired into my cellar lights.

Now my cellar is my workshop and my office. It is where my tools live, my computers live, my Hi-Fi and my life are there. Naturally it was the first place I wanted to experiment with. It divides into four spaces and I long ago wired the lights to control the spaces independently under a master switch at the top of the stairs. What I wanted to do first was to bring them under home automation with my phone, my computers and even Alexa as inputs.

I obtained the Sonoff units from Amazon and they can be controlled by a phone/web App that is cloud based but flashing them with open source code from Theo Arends (see here) puts them on the MQTT protocol and hence puts them right into the hands of homeassistant.

To give you some idea how amusing taking proper control of what is basically just a cheap smart switch can be the in the picture above that shows the two Sonoff Duals that control my four cellar lighting areas you will see a black box on the right which contains a cheap and simple PIR sensor. The box it is in actually cost more than the PIR itself but is a pretty good investment as it keeps my fingers out of the mains voltages. The PIR is powered from the Sonoff's internal power and its output is wired back to a spare pin on the controller chip in the Sonoff Dual alongside it and it reports any activity on the stairs. Homeassistant then combines this signal with the 'usual' switch for that room and automatically turns the light there on for 20 seconds if it is needed (those particular lights are actually controlled by the other 'Dual'). The 'usual' switch is part of a group of all the things in the cellar that I might switch on (desk lights, printers, scanner et al) that will all be turned off together when I finish for the night so nothing gets left on.

In my bedroom lives a laptop and if it is running out of battery I switch on the charger. Now that this is on a smart switch switching it on is just an Alexa command rather than grovelling under the bed and it is automatically switched off at 5AM when it has had plenty of time to charge and does not rely on me to remember to do anything. Also, being a soft old grandfather now, I have an electric blanket to pre-warm the bed at night and this turns on with a homeassistant timer. Well it does unless it was a warm summer's day, which it checks with the met office website, and so it knows I won't need it. If I am out however it postpones turning things on until I get home so I don't get roasted.

Right! Let's implement a switch. Well two actually.

Flashable switches.
I discuss using the Tasmota firmware more carefully on the page about the SWA1 smart plugs but if you use that be sure to compile in your own Wi-Fi name and password so the plug comes straight up on the router. This saves a lot of faffing about. Once you've flashed in the new code you can run the switch on the bench using the flasher's power so it should sign on with the router and be assigned an IP address. Look it up. It's name will usually be Sonoff but I often just got some noise characters. If that happens just try a couple of possibilities. The router will give you an address like 192.168.1.123. Type this into your PC browser's address bar and hope to see the Tasmota basic screen.

1: Select Configuration then Configure Module. Set the Module type correctly. When you click save it saves then reboots itself.

2: Configure MQTT. Set the Host address to the fixed IP you gave the Pi and set the port to 1883. Put in the username and password you used when setting up the mosquitto MQTT broker. I have it on a post-it stuck on the wall. Give it a unique name in Topic. Mine are sonoff01, sonoff02 etc.

3: Configure Other and put that name (sonoff01) in as Friendly name 1. If you have multiple outlets I made the others sonoff01B etc.

4: Go to the Console and see what's happening.
What we are hoping for is MQT: messages. Pushing the button on the Sonoff will turn things on or off and send more. Something like: 
19:01:49 MQT: stat/sonoff01/RESULT = {"POWER1":"OFF"}
This is a Dual so the two messages are identified as POWER1 and POWER2 while a single is just POWER.

5: While you're on the console type in the command 
PowerRetain 1
so it send the instruction to mosquitto to retain the status across restarts.

By now it should have signed on with the mosquitto broker on the Pi so let's configure the homeassistant end. We want to add a switches: section with one entry. (observe the indenting very closely) 
switches:
  - platform: mqtt
    name: "base_stores"                                  (use your preferred name here but lowercase only)
    state_topic: "stat/sonoff01/POWER1"                  (see the notes below)
    command_topic: "cmnd/sonoff01/power1"
    qos: 0
    payload_on: "ON"
    payload_off: "OFF"
    optimistic: false
    retain: true
MQTT is nice and simple. You have a name like "stat/sonoff01/POWER1" and if something on the network posts a message to that name all the other things on the network that subscribed to that name get sent a copy. So here we subscribe to a "state_topic:" which returns us a message. If that message matches our "payload_on:" we read the device as on and if it matches "payload_off:" it is off. The payloads could be anything provided we agree what string of characters is on and what is off we don't care. Similarly the message name can be anything and you just put into homeassistant here and it works. The reason the names come in layers like stat/sonoff01/POWER1 is because you can subscribe to stat/sonoff01/POWER1 or stat/sonoff01 and get all sonoff01 messages or even just stat to get all stat messages from, in this case, all devices but nothing in the spec says anything about the meanings of the layers.
To go the other way we have a "command_topic:" and this time homeassistant sends the payload strings and the sonoff has subscribed them.

Restart homeassistant and as this is the first time mqtt was mentioned it downloads the mqtt module and starts up. What you should see on the Overview page is:

and clicking the switch should elucidate the lights on the Sonoff changing. Once you get it reassembled and the case closed so you can put mains on it you should have relay clicks.
You have a switch! Go on. Wire something into it. You know you want to.

Broadlink emulation
This one's a bit more messy. I have a little 'RM mini' that only does Infra-red signalling so it has been relegated to driving the motor on the bedroom curtains and a 'RM Pro+' that does Infra-red and 400MHz radio. You need your phone with Broadlink's e-Control App loaded.

Now I'm not going to pretend that e-Control isn't pretty flakey software so expect to have to kill it and restart if things go ape on you but bear with me.
I'll do this talking about a 4-button switch controller remote but it worked just the same way for my TV. First you need to set up e-Control so select add a device (their controller thing) and go through that first and give it a name.
Then select add a remote (your handset/tv remote/push button pad) and we have to send each of the button codes in turn to the controller. The trick to this is to get it into 'ready to read' mode, blip the button (do not hold it down except if you have to do the scan radio trick in which case it will do the button as a separate operation after it has found the signal) and wait. If it didn't get it let it time out and do it again. Multiple presses just mess things up and there is no way to back-up once it has something recorded even if it doesn't work.
Test everything so you know the App works then make a nice empty folder on your PC, I called mine broadlink codes and it was below my general automation stuff. Then go to github download the package and extract getBroadlinkSharedData.py.
Then download and install the python 2.7.14 for windows msi from python.org checking the option to add it to the path.
Back to e-Control on the phone and find Share on the main menu | Share to other phones in WLAN and then Cancel because it creates the files you want at once. I used a USB cable into my Galaxy S8 and found them at 
  phone/Internal storage/broadlink/newremote/SharedData
so I dragged the required jsonSubIr, jsonButton and jsonIrCode into the same folder as the py

When I ran python getBroadlinkSharedData.py it failed so, after working on my python education for a bit, I edited 
   import simplejson as json
into 
   import json
and it listed its devices and I chose the name I gave it and it gave me a bunch of stuff like this for each button: 
Button Name: 
Button ID: 46
Code: b20e320015081508150815081508071615080715150815080716071507160716071607150715071515080715081515081508140807dc000000000000
Base64: 
sg4yABUIFQgVCBUIFQgHFhUIBxUVCBUIBxYHFQcWBxYHFgcVBxUHFRUIBxUIFRUIFQgUCAfcAAAA
AAAA
The bit we want is the Base64: bit from sg4.. up to and including the 4 As and the next 4 As that have wrapped to the next line. If you don't get 8 As then it didn't work and you then add two == so the final string is 
sg4yABUIFQgVCBUIFQgHFhUIBxUVCBUIBxYHFQcWBxYHFgcVBxUHFRUIBxUIFRUIFQgUCAfcAAAAAAAA==
You end up with a list of strings and they must all be the same length.

Right. Go to the router, find the Broadlink and give it a fixed IP so homeassistant can find it. Also note down its mac address.

Now I'm not sure how to attach a button to a button number so I just copied them all out as arbitrary on/offs and reordered them after testing. Normally they were just in the order I recorded them in.

Here is an example switch for your configuration file 
  - platform: broadlink
    host: 192.168.1.225
    mac: '34:EA:34:42:C3:2B'
    type: rm2_pro_plus
    timeout: 15
    switches:
      testing123:
        command_on:  'sg4yABUIFQgVCBUIFQgHFhUIBxUVCBUIBxYHFQcWBxYHFgcVBxUHFRUIBxUIFRUIFQgUCAfcAAAAAAAA=='
        command_off: 'sg4yABUIFQgVCBUIFQgHFRUIBxYVCBQIBxUHFQcVBxUIFQcWBxYHFhUHCBUHFhUIFQgHFQfcAAAAAAAA=='
Yes, it isn't a nice blue blob switch but two lightning zig-zags but if you read up on customize: you can slot in an item to fix that. 
  customize:
    switch.testing123:
      assumed_state: false

Incidentally, store away for future reference, that you can use the strings in scripts too 
  run_broadlink:
    sequence:
      - service: switch.broadlink_send_packet_192_168_1_225
        data:
          packet: 
            - 'sgkyABUIFQgVCBQIFQgHFRUIBxUVCBUIBxUHFQcVBxUHFQcVBxUHFRUIBxYVCBUIFQgVCAfcAAAAAAAA=='
It's obviously tea time again.