Receive SML readings from a ISKRA MT 175

Hardware

To monitor the current consumption of my house, I built a DIY PCB with an ESP32 that receives Smart Meter Language (SML) datagrams from an ISKRA MT 175 polyphase meter. I used components I already had in my workshops. So some of them are THT.
The board deliberatly uses an ESP32-WROOM-UE as this module does not come with an PCB antenna. As the ISKRA MT 175 is mounted in an control cabinet, the PCB antenna would be too weak and I would not be able to send the data to an MQTT broker.

Schematics

The board is power by an AM1117 ldo, that converts a 5V input voltage into 3.3 V for the ESP and the peripherals.

The rest is a rather simple ESP32-WROOM-UE module. To be able to debug/flash this device with an ESP-Prog, I connected TXD0, RXD0, EN and GPIO connector and added a Jumper (J4 on the PCB) for power selection (5V versus 3.3V). GPIOs 16 and 17 are used to receive data from a small PCB that cares about the reception of infrared signals from the ISKRA MT 175. GPIO13 is connected to an LED that can be used to indicate reception mode.
Note that connectors J6 and J6 are used to connect to a piggy board that that receives the infrared signals from ISKRA MT 175.
I was planning to etch the PCB on my own. Hence the PCB is planned to be a one sided PCB.

The Code

The code can be found on github here