Energy Meter Gateway with ESP8266

• Receive messages from IR serial interface and post them on syslog and influx database
• Validate meter readings against configured power limits to reject bogus data
• Optionally send power status (feeding to grid or high load) to WLED with UDP
• Optionally set limit of an OpenDTU inverter via MQTT to avoid high feed to grid
• Modern web UI with live power and per-period consumption (today, yesterday, this/last week, month, year)

Web UI

The device serves a small set of pages; every page links to the others with a consistent dark-themed nav bar:

• / – Home: live power, meter status, optional inverter and WLED cards
• /monitor – auto-refreshing live power plus consumption for today, yesterday, this/last week, month and year. On the first valid reading after boot the device queries InfluxDB for the meter value at-or-after the start of each period so consumption stays correct across reboots; periods with no historical data show a dash.
• /wled – WLED settings: runtime-configurable color thresholds, hysteresis delays, colors, and a toggle for WLED live-receive mode (only shown when WLED_LEDS is defined)
• /json – stable JSON API (unchanged across versions)
• /sml – last raw SML record (binary download, unchanged)
• /update – OTA firmware upload
• POST /reset – reboot the device

Features

Meter Reading Validation

Readings are validated against configured maximum power thresholds (PROD_KW_MAX, USAGE_KW_MAX) to detect and reject anomalous data from the meter. If any reading exceeds the limits, the entire SML message is discarded as invalid. Rejected readings are never forwarded to InfluxDB, MQTT, WLED, or the live power display; the next reading is always compared against the last accepted baseline.

Two classes of outlier are detected:

Backwards readings — the A+ or A- counter is lower than the previous accepted value, which can indicate a transient bit error in the SML stream or a genuine meter reset after a power failure. Isolated bit errors are common and expected; a sustained run means the meter actually reset.

Power-limit spikes — the energy delta between two consecutive readings implies a power level that exceeds the configured maximum, which is physically impossible and indicates a corrupt reading.

Syslog messages

Every message below is at LOG_NOTICE or higher and appears under the device hostname.

Message	Meaning
Backwards #N: A+=X (was Y) A-=P (was Q)	N-th consecutive backwards reading in the current run. X/P are the new (rejected) values; Y/Q are the last accepted values. A single #1 followed by a normal reading is a harmless bit error.
Meter reset confirmed after N backwards readings, new baseline A+=X A-=Y	N consecutive backwards readings were seen — interpreted as a genuine meter reset after power loss. The baseline is updated and the live power display is cleared.
Rejected: A+ delta=D/10 Wh in T s = K.KK kW, limit=L kW	A+ energy jump of D/10 Wh over T seconds implies K.KK kW, exceeding the USAGE_KW_MAX limit of L kW. Reading discarded.
Rejected: A- delta=D/10 Wh in T s = K.KK kW, limit=L kW	Same for A- (backfeed), compared against PROD_KW_MAX.
Stats: T readings, A accepted, B backwards (R runs, max M in a row), P power-rejected	Periodic summary (~once per minute). T is total valid SML frames parsed; A accepted; B discarded as backwards across R separate runs with a longest run of M; P discarded for exceeding the power limit.
Itron valid=…	Periodic confirmation of a good reading (once per minute).

Interpreting the Stats line

• B=0 — no outliers in the last minute, everything clean.
• B>0, R=B, max=1 — every backwards reading was isolated (one per run). Classic bit-error pattern, not a problem.
• B>0, max>1 — consecutive backwards readings in a cluster. Runs of 2–3 occasionally happen; 4 means one more would have triggered a meter-reset declaration.
• max≥5 — a meter reset was confirmed; check for a preceding Meter reset confirmed warning.
• P>0 — power-limit spikes occurred; inspect the individual Rejected lines to see how far the values exceeded the threshold. If the computed kW is only marginally above the limit, consider raising USAGE_KW_MAX / PROD_KW_MAX.

WLED Visual Feedback

Enabled if WLED_LEDS is defined. Provides color-coded visual feedback via WLED using UDP protocol (DRGB).

Color thresholds and priority (highest wins; all configurable via /wled or platformio.ini):

Priority	Color	Condition	Default threshold
1 (highest)	Green	Backfeed too high (> WLED_BACKFEED_TOO_HIGH W)	7000 W
2	Red	Consumption high (> WLED_CONSUMPTION_HIGH W)	4000 W
3	Blue	Good backfeed (> WLED_BACKFEED_GOOD W)	500 W
4 (lowest)	Violet	Daytime error (no meter / DB / MQTT for too long)	WLED_DAY_START–WLED_DAY_END

All colors use configurable hysteresis delays to avoid rapid flickering.

Dynamic OpenDTU Inverter Limit

Enabled if DTU_TOPIC is defined. Automatically adjusts the inverter power limit via MQTT to keep grid backfeed within a target range (BACKFEED_MIN to BACKFEED_MAX).

Note: Set BACKFEED_MIN = BACKFEED_MAX to disable automatic limit adjustment (inverter runs at maximum).

Configuration in platformio.ini:

• INVERTER_LIMIT - Maximum inverter output (W)
• BACKFEED_MIN / BACKFEED_MAX - Target backfeed range (W)
• LIMIT_CHECK_INTERVAL_S - Minimum seconds between adjustments
• LIMIT_ROUND_GRANULARITY - Round limit changes to multiples of this value (W)

The MQTT topic format is: DTU_TOPIC/INVERTER_SERIAL/cmd/limit_nonpersistent_absolute

Hardware

• Wemos Mini D1 ESP8266
• IR LED (940nm) used as photodiode receiver
• NPN transistor (e.g. BC546)

        3.3V
         │
       [10kΩ]
         │
         ├──────────────── GPIO Rx (Serial)
         │
         C
         │
        ─┤
   B ───┤   NPN (BC546)
   │    ─┤
   │     │
   │     E
   │     │
   ▼     │     IR LED (940nm)
  ─┴─    │      ▼  = anode (+)
   │     │     ─┴─ = cathode bar (−)
   │     │
   └─────┴── GND

The IR LED acts as a photodiode: meter IR pulses generate a small photocurrent into the NPN base, pulling the collector low against the 10 kΩ pull-up to 3.3V. The resulting active-low signal feeds the hardware serial Rx pin.

Building and Uploading

# Activate PlatformIO environment
. ~/.platformio/penv/bin/activate

# Build
platformio run

# Upload via OTA (requires hostname/instance configured)
platformio run --target upload

# Upload via USB
# Set upload_port in platformio.ini first
platformio run --target upload --upload-port /dev/ttyUSB0

Grafana Dashboard

Configuration

All power limits and thresholds are configurable in platformio.ini under the [program] section:

# Meter reading validation (reject bogus readings)
prod_kw_max = 15          # Max production/feed-in power (kW)
usage_kw_max = 20         # Max consumption power (kW)

# WLED visual feedback (see /wled page for runtime adjustment)
wled_leds = 60                   # Number of LEDs
wled_brightness = 100            # Master brightness (0–255)
wled_consumption_high = 4000     # Red: high consumption threshold (W)
wled_backfeed_too_high = 7000    # Green: backfeed too high threshold (W)
wled_backfeed_good = 500         # Blue: good backfeed threshold (W)
wled_day_start = 7               # Violet error indicator: start hour (0–23)
wled_day_end = 21                # Violet error indicator: end hour (0–23)

# Inverter control
inverter_limit = 800             # Max inverter output (W)
backfeed_min = 5000              # Target backfeed range min (W)
backfeed_max = 5000              # Target backfeed range max (W) - set equal to min to disable
limit_check_interval_s = 10      # Min seconds between limit adjustments
limit_round_granularity = 100    # Round limits to multiples of this (W)

Copy inverter_template.ini to inverter.ini and set your inverter serial number.

SML Messages

Example message from my itron electricity meter

//0 1   2   3   4   5  level   
76,
    09, ae,01,00,00, 00,10,b6,88,
    62, 00,
    62, 00,
    72,
        65, 00,00,01,01,  // SML open()
        76,
            01,
            01,
            09, 00,00,00,00, 00,05,93,db,
            0b, 0a,01,49,54, 52,xx,xx,xx, xx,xx,
            72,
                62, 01,
                65, 00,05,93,dc,
            01,
    63, f5,44,
    00,
76,
    09, ae,01,00,00, 00,10,b6,89,
    62, 00,
    62, 00,
    72,
        65, 00,00,07,01,  // SML get_list()
        77,
            01,
            0b, 0a,01,49,54, 52,xx,xx,xx, xx,xx,
            07, 01,00,62,0a, ff,ff,
            72,
                62, 01,
                65, 00,05,93,dc,
            74,
                77,
                    07, 01,00,60,32, 01,01,  // obis meter id
                    01,
                    01,
                    01,
                    01,
                    04, 49,54,52,  // "ITR"
                    01,
                77,
                    07, 01,00,60,01, 00,ff,  // 07=6 bytes obis serial no
                    01,  // 01=no data, means default
                    01,
                    01,
                    01,
                    0b, 0a,01,49,54, 52,xx,xx,xx, xx,xx,
                    01,
                77,
                    07, 01,00,01,08, 00,ff,  // obis A+
                    65, 00,1c,01,04,
                    01,
                    62, 1e,  // 6=unsigned, 2=itemLen -> byte data: 0x1e=30 = unit
                    52, 03,  // 5=signed: 0x03=3 = scale
                    69, 00,00,00,00, 00,00,00,5a,  // 6=unsigned, 9=itemLen -> dword: 0x5a
                    01,
                77,
                    07, 01,00,02,08, 00,ff,  // obis A-
                    01,
                    01,
                    62, 1e,
                    52, 03,
                    69, 00,00,00,00, 00,00,00,00,
                    01,
            01,
            01,
    63, 3c,dc, 
    00,
76,
    09, ae,01,00,00, 00,10,b6,8a,
    62, 00,
    62, 00,
    72,
        65, 00,00,02,01,  // SML close()
        71,
            01,
    63, 67,a9,
    00,
00,00,

Documentation

• http://www.schatenseite.de/2016/05/30/smart-message-language-stromzahler-auslesen/
• https://www.bsi.bund.de/SharedDocs/Downloads/DE/BSI/Publikationen/TechnischeRichtlinien/TR03109/TR-03109-1_Anlage_Feinspezifikation_Drahtgebundene_LMN-Schnittstelle_Teilb.pdf?__blob=publicationFile
• https://www.edi-energy.de/index.php?id=38&tx_bdew_bdew%5Buid%5D=1158&tx_bdew_bdew%5Baction%5D=download&tx_bdew_bdew%5Bcontroller%5D=Dokument&cHash=4ee767287a68d3f0fbbc3caf2974d97f
• https://www.itron.com/-/media/feature/products/documents/brochure/openway_kl.pdf
• https://www.devolo.ch/fileadmin/Web-Content/DE/products/sg/3hz-basiszaehler/documents/de/Handbuch_devolo_3.HZ_Basiszaehler_D3B60_D3B100_0419_Online_DE.pdf