DD3-LoRa-Bridge-MultiSender

Firmware for LilyGO T3 v1.6.1 (ESP32 + SX1276 + SSD1306) that runs in two roles:

• Sender (GPIO14 HIGH): reads one IEC 62056-21 meter, builds 30-slot sparse batches, sends via LoRa.
• Receiver (GPIO14 LOW): receives/ACKs batches, publishes MQTT, serves web UI, logs to SD.

Architecture Summary

• Single codebase, role selected at boot by detect_role() (src/config.cpp).
• LoRa transport is wrapped with firmware-level CRC16-CCITT (src/lora_transport.cpp).
• Sender meter ingest is decoupled from LoRa waits via FreeRTOS meter reader task + queue on ESP32 (src/main.cpp).
• Batch payload codec is schema v3 with a 30-bit present_mask over [t_last-29, t_last] (src/payload_codec.cpp).
• Sender only starts normal metering/transmit flow after valid time bootstrap from receiver ACK.
• Receiver runs STA mode if stored config is valid and connects, otherwise AP fallback.

LoRa Protocol

On-air frame:

[msg_kind:1][device_short_id:2][payload...][crc16:2]

msg_kind:

• 0: BatchUp
• 1: AckDown

BatchUp

Transport layer chunks payload into:

[batch_id_le:2][chunk_index:1][chunk_count:1][total_len_le:2][chunk_payload...]

Receiver reassembles all chunks before decode.

Payload codec (schema=3, magic 0xDDB3) carries:

• metadata: sender ID, batch ID, t_last, present_mask, battery mV, error counters
• arrays per present sample: energy_wh[], p1_w[], p2_w[], p3_w[]

n == 0 with present_mask == 0 is valid and used for sync request packets.

AckDown (7 bytes payload)

[flags:1][batch_id_be:2][epoch_utc_be:4]

• flags bit0: time_valid
• ACK is repeated (ACK_REPEAT_COUNT=3, ACK_REPEAT_DELAY_MS=200)
• Sender sets local time only if time_valid=1 and epoch >= MIN_ACCEPTED_EPOCH_UTC (2026-02-01 00:00:00 UTC)

Time Bootstrap and Timezone

Sender boot starts in sync-only mode:

• g_time_acquired=false
• sends sync requests every SYNC_REQUEST_INTERVAL_MS (15s)
• does not run normal 1 Hz sample/batch flow yet

After valid ACK time:

• time_set_utc() is called
• g_time_acquired=true
• normal 1 Hz sampling + periodic batch transmission starts

Timezone:

• TIMEZONE_TZ from include/config.h is applied in time_manager.
• Web/OLED local-time rendering uses this timezone.
• Default: CET-1CEST,M3.5.0/2,M10.5.0/3.

Sender Meter Path

Implemented by src/meter_driver.cpp and sender loop in src/main.cpp:

• UART: Serial2, GPIO34, 9600 7E1
• ESP32 RX buffer enlarged to 8192
• Frame detection / ... !, timeout METER_FRAME_TIMEOUT_MS=3000
• Parsed OBIS fields:
  • 0-0:96.8.0*255 meter Sekundenindex (hex u32)
  • 1-0:1.8.0 total energy (auto scales Wh -> kWh when unit is Wh)
  • 1-0:16.7.0 total active power
  • 1-0:36.7.0, 56.7.0, 76.7.0 phase powers

Timestamp derivation:

• anchor offset: epoch_offset = epoch_now - meter_seconds
• sample epoch: ts_utc = meter_seconds + epoch_offset
• jump checks: rollback, wall-time delta mismatch, anchor drift

Sender builds sparse 30-slot windows and sends every METER_SEND_INTERVAL_MS (30s).

Receiver Behavior

For decoded BatchUp:

1. Reassemble and decode.
2. Send AckDown immediately.
3. Track duplicates per configured sender (EXPECTED_SENDER_IDS).
4. If duplicate: update duplicate counters/time, skip data write/publish.
5. If n==0: sync request path only.
6. Else reconstruct each sample timestamp from t_last + present_mask, then:
   • append to SD CSV
   • publish MQTT state
   • update web status and last batch table

MQTT

State topic:

• smartmeter/<device_id>/state

Fault topic (retained):

• smartmeter/<device_id>/faults

State JSON (src/json_codec.cpp) includes:

• id, ts, e_kwh
• p_w, p1_w, p2_w, p3_w
• bat_v, bat_pct
• optional link: rssi, snr
• err_last, rx_reject, rx_reject_text
• non-zero fault counters when available

Home Assistant discovery:

• enabled by ENABLE_HA_DISCOVERY=true
• publishes to homeassistant/sensor/<device_id>/<key>/config

Web UI, Wi-Fi, SD

• Wi-Fi/MQTT/NTP/web-auth config is stored in Preferences.
• AP fallback SSID prefix: DD3-Bridge-.
• Default web credentials: admin/admin.
• AP auth requirement is controlled by WEB_AUTH_REQUIRE_AP (default false).
• STA auth requirement is controlled by WEB_AUTH_REQUIRE_STA (default true).

Web timestamp display:

• human-facing timestamps show epoch (HH:MM:SS TZ) in local configured timezone.

SD CSV logging (src/sd_logger.cpp):

• header: ts_utc,ts_hms_utc,p_w,p1_w,p2_w,p3_w,e_kwh,bat_v,bat_pct,rssi,snr,err_m,err_d,err_tx,err_last
• ts_hms_utc is UTC HH:MM:SS

History parser (src/web_server.cpp):

• expects the current CSV layout above
• legacy CSV layouts are not parsed (no backward compatibility)

OLED duplicate display:

• receiver sender-pages show duplicate rate as pct (absolute) and last duplicate as HH:MM.

Build Environments

From platformio.ini:

• lilygo-t3-v1-6-1
• lilygo-t3-v1-6-1-test
• lilygo-t3-v1-6-1-868
• lilygo-t3-v1-6-1-868-test
• lilygo-t3-v1-6-1-payload-test
• lilygo-t3-v1-6-1-868-payload-test
• lilygo-t3-v1-6-1-prod
• lilygo-t3-v1-6-1-868-prod

Example:

python -m platformio run -e lilygo-t3-v1-6-1

Test Mode

ENABLE_TEST_MODE replaces normal loops with test_sender_loop / test_receiver_loop (src/test_mode.cpp):

• Sender emits periodic JSON test payloads over LoRa.
• Receiver decodes test payloads, updates display test codes, publishes MQTT to:
  • smartmeter/<device_id>/test