During the last month, our engery supplier installed a digital meter for our power usage at home. As he in addition to that offered to unlock the device or to give us the PIN to unlock it ourselves, I were looking for a solution to extract the data from the meter and push it into our Home Assistant installation. I bought the Volkszähler TTL from eBay and wired it onto the serial interface of an ESP8266 laying around on my desk. The seller shared me two links to YouTube videos (https://youtu.be/RbyXqJiBC8Q, https://youtu.be/VuXpzKetOhc), where he explains how to modify and build the Tasmota firmware to include the SML interface to the power meter.
In parallel, I unlocked the meter via the PIN supplied by the energy supplier, setting the INFO option to ON and the PIN parameter to OFF. Once that was set I attached the IR sensor to the power meter weith a ring magnet and voiala, the SML diagrams popped up in the console of the Tasmato WebUI. I used the following website to decode the SML dump from Tasmota to find the right values for my powermeter and once the script was updated in the configuration, Tasmota now correclty decodes and shows the data in the WebUI.
>D >B =>sensor53 r >M 1 +1,3,s,0,9600,SML 1,77070100600100ff@#,Zaehlernummer,,meter_number,0 1,77070100010800ff@1000,Total In,kWh,total_in,4 1,77070100020800ff@1000,Total Out,kWh,total_out,4 1,77070100100700ff@1,Power Current,W,power_curr,4 #
Once MQTT is enabled, the data automatically pops up in Home Assistant where I can use it now in our energy dashboard.