Getting a working MQTT temperature monitoring setup is neat, but not really what we think of when someone talks about home automation. For that we need some element of control. There are various intelligent light bulb systems out there that are obvious candidates, but I decided I wanted the more simple approach of switching on and off an existing lamp. I ended up buying a pair of Sonoff Basic devices; I’d rather not get into trying to safely switch mains voltages myself. As well as being cheap the Sonoff is based upon an ESP8266, which I already had some experience in hacking around with (I have a long running project to build a clock I’ll eventually finish and post about). Even better, the Sonoff-Tasmota project exists, providing an alternative firmware that has some support for MQTT/TLS. Perfect for my needs!

There’s an experimental OTA upgrade approach to getting a new firmware on the Sonoff, but I went the traditional route of soldering a serial header onto the board and flashing using esptool. Additionally none of the precompiled images have MQTT/TLS enabled, so I needed to build the image myself. Both of these turned out to be the right move, because using the latest release (v5.13.1 at the time) I hit problems with the device rebooting as soon as it got connected to the MQTT broker. The serial console allowed me to see the reboot messages, and as I’d built the image myself it was easy to tweak things in the hope of improving matters. It seems the problem is related to the memory consumption that enabling TLS requires. I went back a few releases until I hit on one that works, with everything else disabled. I also had to nail the Espressif Arduino library version to an earlier one to get a reliable wifi connection - using the latest worked fine when the device was power via USB from my laptop, but not once I hooked it up to the mains.

Once the image is installed on the device (just the normal ESP8266 esptool write_flash 0 sonoff-image.bin approach), start mosquitto_sub up somewhere. Plug the Sonoff in (you CANNOT have the Sonoff plugged into the mains while connected to the serial console, because it’s not fully isolated), and you should see something like the following:

$ mosquitto_sub -h mqtt-host -p 8883 --capath /etc/ssl/certs/ -v -t '#' -u user1 -P foo
tele/sonoff/LWT Online
cmnd/sonoff/POWER (null)
tele/sonoff/INFO1 {"Module":"Sonoff Basic","Version":"5.10.0","FallbackTopic":"DVES_123456","GroupTopic":"sonoffs"}
tele/sonoff/INFO3 {"RestartReason":"Power on"}
stat/sonoff/RESULT {"POWER":"OFF"}
stat/sonoff/POWER OFF
tele/sonoff/STATE {"Time":"2018-05-25T10:09:06","Uptime":0,"Vcc":3.176,"POWER":"OFF","Wifi":{"AP":1,"SSId":"My SSID Is Here","RSSI":100,"APMac":"AA:BB:CC:12:34:56"}}

Each of the Sonoff devices will want a different topic rather than the generic ‘sonoff’, and this can be set via MQTT:

$ mosquitto_pub -h -p 8883 --capath /etc/ssl/certs/ -t 'cmnd/sonoff/topic' -m 'sonoff-snug' -u user1 -P foo

The device will provide details of the switchover via MQTT:

cmnd/sonoff/topic sonoff-snug
tele/sonoff/LWT (null)
stat/sonoff-snug/RESULT {"Topic":"sonoff-snug"}
tele/sonoff-snug/LWT Online
cmnd/sonoff-snug/POWER (null)
tele/sonoff-snug/INFO1 {"Module":"Sonoff Basic","Version":"5.10.0","FallbackTopic":"DVES_123456","GroupTopic":"sonoffs"}
tele/sonoff-snug/INFO3 {"RestartReason":"Software/System restart"}
stat/sonoff-snug/RESULT {"POWER":"OFF"}
stat/sonoff-snug/POWER OFF
tele/sonoff-snug/STATE {"Time":"2018-05-25T10:16:29","Uptime":0,"Vcc":3.103,"POWER":"OFF","Wifi":{"AP":1,"SSId":"My SSID Is Here","RSSI":76,"APMac":"AA:BB:CC:12:34:56"}}

Controlling the device is a matter of sending commands to the cmd/sonoff-snug/power topic - 0 for off, 1 for on. All of the available commands are listed on the Sonoff-Tasmota wiki.

At this point I have a wifi connected mains switch, controllable over MQTT via my internal MQTT broker.

(If you want to build your own Sonoff Tasmota image it’s actually not too bad; the build system is Ardunio style on top of PlatformIO. That means downloading a bunch of bits before you can actually build, but the core is Python based so it can be done as a normal user within a virtualenv. Here’s what I did:

# Make a directory to work in and change to it
mkdir sonoff-ws
cd sonoff-ws
# Build a virtual Python environment and activate it
virtualenv platformio
source platformio/bin/activate
# Install PlatformIO core
pip install -U platformio
# Clone Sonoff Tasmota tree
git clone
cd Sonoff-Tasmota
# Checkout known to work release
git checkout v5.10.0
# Only build the sonoff firmware, not all the language variants
sed -i 's/;env_default = sonoff$/env_default = sonoff/' platformio.ini
# Force older version of espressif to get more reliable wifi
sed -i 's/platform = espressif8266$/&@1.5.0/' platformio.ini
# Edit the configuration to taste; essentially comment out all the USE_*
# defines and enable USE_MQTT_TLS
vim sonoff/user_config.h
# Actually build. Downloads a bunch of deps the first time.
platformio run

I’ve put my Sonoff-Tasmota user_config.h up in case it’s of help when trying to get up and going. At some point I need to try the latest version and see if I can disable enough to make it happy with MQTT/TLS, but for now I have an image that does what I need.)