I’m getting a sauna installed and it has a Modbus-RTU interface which I’d like to use to control the sauna using home assistant. I’ve looked at the docs and things look relatively straight-forward.
However, I am completely new to Modbus, and could use some advice getting this up and running. The first question I have is how to get HA to connect to the Sauna over Modbus. As I understand it I need a Gateway to convert Modbus-RTU to Modbus-TCP.
Can anyone recommend a good and not-too-expensive device that does this? I see loads of options, with wildly varying prices (50-500 euros). Ethernet is fine, Wifi would also be fine. The sauna has an RS-485 connection (three wires). Ideally I can configure the gateway using a webpage or a Mac tool (I’ve noticed that most need to be configured using a windows utility, which isn’t great for me as I don’t have a Windows machine).
Thanks! Sounds really interesting, but I’ve also never used ESPHome before . I imagine I need a microcontroller which I will need to flash with ESPHome, and make sure that the board has the right connections? (power, wifi/ethernet, serial) Is there a board you recommend?
In the mean time I found this which is more expensive but seems to do what I need – I think?
Indeed, but nowadays we just say “install” because it’s so easy
Well all esp’s come with wifi (some come without atenna actually) and for ethernet you need a esp32.
In general a $2 D1 Mini (esp8266 - wifi only) should actually cover your needs and comes with onboard serial and micro-usb (or usb-c for v4) connector.
About the “right connections”: ESP’s have plenty of GPIO’s - depending on your needs you can also add port extenders or (in case you use a esp82xx) upgrade to a esp32 (some boards include Ethernet/PoE btw.)
Might be (I have no idea actually ) but I expect that most of the solutions only allow you to “own” the hardware and the software part will be a black box forever (including whatever limitations they have). On the opposite ESPHome allows you full ownership of your esp’s and is highly expandable. For example you could add Display and some controls to your esp and it will able to control stuff that way
. I imagine I need a microcontroller which I will need to flash with ESPHome, and make sure that the board has the right connections? (power, wifi/ethernet, serial) Is there a board you recommend?
) but I expect that most of the solutions only allow you to “own” the hardware and the software part will be a black box forever (including whatever limitations they have). On the opposite ESPHome allows you full ownership of your esp’s and is highly expandable. For example you could add Display and some controls to your esp and it will able to control stuff that way 
