Help with SDM630-MODBUS and Sonoff Basic

[hahmann]

Make sure these boxes are checked [x] before submitting your issue - Thank you!

• Searched the problem in issues (https://github.com/arendst/Sonoff-Tasmota/issues)
• Searched the problem in the wiki (https://github.com/arendst/Sonoff-Tasmota/wiki/Troubleshooting)
• Searched the problem in the forum (https://forum.digital-pig.com/)
• Searched the problem in the discussion group (https://groups.google.com/d/forum/sonoffusers)
• Hardware used : SDM630 + Sonoff Basic
• Provide the output of command status 0 :

STATUS 0 OUTPUT HERE
22:32:17 CMD: status 0
22:32:17 MQT: stat/irrigation_valve_2/STATUS = {"Status":{"Module":1,"FriendlyName":["irrigation_valve_2"],"Topic":"irrigation_valve_2","ButtonTopic":"0","Power":0,"PowerOnState":3,"LedState":1,"SaveData":1,"SaveState":1,"ButtonRetain":0,"PowerRetain":0}}

I'm trying to connect SDM630-MODBUS to Sonoff Basic, I have the following configuration for gpio:
22:33:52 CMD: gpio
22:33:52 MQT: stat/irrigation_valve_2/RESULT = {"GPIO1":"78 (SDM630 Rx)","GPIO3":"77 (SDM630 Tx)","GPIO4":"0 (None)","GPIO14":"0 (None)"}

But could not find anything on the wiki showing the connection between SDM630 and sonoff serial interface, so not sure I'm missing any hardware to do the RS485 to serial on sonoff.

Really appreciate any help here.

Thanks,
Gabriel.

[Frogmore42]

RS-485 defines the voltage levels, so you absolutely need to have an RS-485 to TTL converter. There are some ways to do some things without one, but they lose the noise immunity of rs-485 and you have to know what you are doing or get lucky to make them work.

[Jason2866]

You need on the hardware side something like this:
https://www.aliexpress.com/item/TTL-to-RS485-Power-Supply-Converter-Board-3-3V-5V-Hardware-Auto-Control-Module-For-Arduino/32852445547.html?spm=2114.search0104.3.8.25cf7ef6uZpUdg&ws_ab_test=searchweb0_0,searchweb201602_2_10320_10152_10151_10065_10321_10344_10068_10342_10547_10343_10322_10340_10548_10341_10696_10084_10083_10618_10304_10307_10820_10821_10302_10846_10843_10059_100031_10319_10103_524_10624_10623_10622_10621_10620,searchweb201603_2,ppcSwitch_5&algo_expid=37782e0c-481a-4aa5-9c66-cd0a21b484bf-1&algo_pvid=37782e0c-481a-4aa5-9c66-cd0a21b484bf&priceBeautifyAB=0

[hahmann]

Perfect, thank you @Frogmore42 and @Jason2866, I managed to make the connection work using a MAX3486 I had here and did my own adapter with automatic TX/RX, it is working properly and as expected reporting to sonoff-tasmota.