esp32_watermeter

WiFi-connected ESP32 reader for the household water meter (Sagemcom Siconia WM20-L / SK20-MI001-SMU061, installed by VASYD), publishing consumption to Home Assistant.

Status: production firmware flashed and confirmed working end-to-end (2026-09-10) — the ESP32-C6 + PN5180 reader, wired per docs/wiring.md, reads the meter's NFC tag, and publishes state + Home Assistant MQTT-discovery config to the rpi7.local broker, all verified live. See "Production firmware" below.

The meter's LoRaWAN uplink is encrypted and off-limits, and its LCD is normally blank (only lights up on the physical wake button — not usable for automated reading). Instead, the meter exposes an ISO 15693 NFC tag (ST25DV04K-I) that holds plaintext daily consumption history. This has been read by hand with a phone (STMicroelectronics "NFC Tap" app) and decoded, then confirmed against a full 512-byte dump captured by the ESP32+PN5180 reader — see docs/findings.md.

Remaining work: OTA manifest hosting is only manual/on-demand for now (see ota/README.md), and the tag's daily update cadence is still being characterized empirically (see "Not done yet" below).

Repo contents

• docs/findings.md — full write-up of the investigation: meter identification, why LoRaWAN/display/camera-OCR were ruled out, the NFC tag details, and the decoded data format.

• docs/dumps/ — raw memory dumps pulled from the tag: early partial dumps via phone (data.bin 124B, mem2.bin/mem3.bin ~396B), and the first complete dump via the ESP32+PN5180 reader (mem_full_esp32_20260910.bin, full 512B).

• docs/analyze_dump.py — script used to find the BCD date fields and volume values in the dumps; rerun against any new dump to re-check/extend the decode.

• docs/bom.md — components to buy, with electrokit.com availability.

• docs/wiring.md — PN5180 ↔ ESP32-C6-DevKitC-1 wiring (pinout, GPIO assignment, safety notes) and the hardware bring-up test plan.

• bringup/PN5180_bringup/ — throwaway Arduino-core sketch used to validate the wiring; not the production firmware.

• esp32/ — the production ESP-IDF firmware (plain C, no Arduino/ESPHome — see "framework" decision in docs/wiring.md). Flashed and confirmed working end-to-end 2026-09-10: WiFi connects, reads the meter tag, and publishes state + availability + Home Assistant MQTT-discovery config to rpi7.local, all verified live on the broker.

Production firmware (esp32/) — status and how to build

WiFi (NVS-backed credentials, mirrors the esp32_bme280 project's wifi.c) + PN5180/ISO15693 driver (ported from wilson-elechouse/PN5180_ELECHOUSE's Arduino source to ESP-IDF's spi_master) + the meter-specific decode + MQTT publish (with a Home Assistant MQTT-discovery config message) + a continuous polling loop.

Polling interval is deliberately short for now (30 min, see POLL_INTERVAL_MS in esp32/main/globals.h) rather than once daily — the tag's update cadence isn't fully characterized yet (see docs/findings.md), so this collects enough samples to see it empirically before dialing back to a more efficient interval. Every published MQTT message includes a changed_since_last field for exactly this purpose.

OTA is wired up matching the esp32_watertank project's convention exactly (ported ota.c/ota.h unchanged): a plain-text manifest (version + .bin URL) polled from OTA_MANIFEST_URL, esp_https_ota to apply it, and the same rollback-safety flow — a freshly-flashed OTA image that can't even reach WiFi triggers an automatic revert to the previous image. MQTT broker corrected to rpi7.local (not rpi4.local as first scaffolded — cross-checked against esp32_watertank's globals.h, which has the same host/broker documented).

Not done yet:

• OTA hosting is manual/on-demand only, not a permanent service — see ota/README.md for publishing an update and starting the staging server.
• WiFi credentials are filled in; MQTT has no auth configured (MQTT_USERNAME/MQTT_PASSWORD empty) — fine if the broker allows anonymous connections, same as esp32_watertank.

To build:

source ~/.espressif/v6.0/esp-idf/export.sh   # or wherever ESP-IDF is installed
cd esp32
idf.py set-target esp32c6   # only needed once
idf.py build
idf.py -p /dev/ttyACM0 flash monitor   # native USB port; use /dev/ttyUSB0 for the UART bridge port instead