We're using Mosquitto as MQTT-Broker, which is served on it's standard port 1883.
MQTT is a widely used protol, to exchange data and information. It's based on a central broker, that manages all incoming data and refers them to connected clients accordingly. The basic concepts are 'Publish' and 'Subscribe'. A client can publish messages under a specific topic, to which other clients can subscribe to and receive these payloads.
Click on 'Config' from the main menu, then head over to 'Relays' and activate 'Wifi Relays'. On the bottom of the corresponding column you'll find a button 'Set Wrelay Firmware'. Click on it and you'll be prompted to a form in which you can set the desired firmware for all wifi-relays.
Connect to your Tasmota devices web-interface. Set 'RPI-IP:1883' as host in your Tasmota devices MQTT settings. then use the relay you want to use for this device as the topic ('wrelay1' to 'wrelay8', case sensitive!). The full topic needs to be 'pkw/%prefix%/%topic%'
Connect to your Shelly switches web-interfaces (do not use the shelly mobile app for this!) Head over to 'Internet & Security' and choose 'Advanced - Developer Settings'. Again, as host set 'RPI-IP:1883'. Activate 'Use custom MQTT prefix' and set it to 'shellyRelay1' up to 'shellyRelay8'.
Please be advised, you won't be able to use the Shelly cloud function via the Shelly app after activating MQTT!
We prepared a Tasmota image with everything preconfigured, all you need to set is the wifi credentials so that your Tasmota device can connect to the broker.
You can flash it by either directly connecting your device to the Raspberry Pi and go to Config -> System -> Flashtool (see here), or use our webflasher at flashesp. You could also download the image from downloads.pekaway.de and flash it in your preferred way.
Further information can be found here: vanpi.de/tutorial-wifi-relays