DD3-LoRa-Bridge-MultiSender

Firmware for LilyGO T3 v1.6.1 (ESP32 + SX1276 + SSD1306) that runs as either:

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

Current Architecture

• Single codebase, role selected at boot via detect_role() (include/config.h, src/config.cpp).
• LoRa link uses explicit CRC16 frame protection in firmware (src/lora_transport.cpp).
• Sender batches up to 30 samples and retries on missing ACK (BATCH_MAX_RETRIES=2, retry policy Keep).
• Receiver uses STA mode when config is valid, otherwise AP fallback with web config.

LoRa Frame Protocol (Current)

On-air frame format:

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

msg_kind:

• 0 = BatchUp
• 1 = AckDown

BatchUp

Transport is chunked (batch_id, chunk_index, chunk_count, total_len) and reassembled before payload decode.

Payload codec (src/payload_codec.cpp) currently uses:

• kMagic=0xDDB3
• kSchema=2
• metadata: sender, batch, timestamp, interval, battery, fault counters
• data arrays: energy_wh[], p1_w[], p2_w[], p3_w[]

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

AckDown (7 bytes)

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

• flags bit0: time_valid
• Receiver repeats ACK (ACK_REPEAT_COUNT=3, ACK_REPEAT_DELAY_MS=200).
• Sender accepts time only if time_valid=1 and epoch >= MIN_ACCEPTED_EPOCH_UTC (2026-02-01 00:00:00 UTC).

Time Bootstrap Guardrail

On sender boot:

• g_time_acquired=false
• no normal sampling/transmit yet
• sync request every SYNC_REQUEST_INTERVAL_MS (15s)

Only after valid ACK time is received:

• system time is set
• normal 1 Hz sampling and periodic LoRa batch transmit start

This blocks pre-threshold timestamps from MQTT/SD paths.

Sender Meter Path

Implemented in src/meter_driver.cpp + sender loop in src/main.cpp:

• UART: Serial2, RX pin GPIO34 (PIN_METER_RX), 9600 7E1
• Frame detection: starts at '/', ends at '!', timeout protection included
• Parsed OBIS values:
  • 1-0:1.8.0 (total energy)
  • 1-0:16.7.0 (total power)
  • 1-0:36.7.0, 56.7.0, 76.7.0 (phase powers)
• 1-0:1.8.0*Wh is automatically scaled to kWh

Sender samples every second and transmits batches every 30 seconds.

Receiver Behavior

For valid BatchUp decode:

1. Reassemble chunks and decode payload.
2. Send AckDown immediately.
3. Drop duplicate batches per sender (batch_id tracking).
4. If n==0: treat as sync request only.
5. Else convert samples, log to SD, update web UI, publish MQTT.

MQTT Topics and Payloads

State topic:

• smartmeter/<device_id>/state

Fault topic (retained):

• smartmeter/<device_id>/faults

State JSON fields (src/json_codec.cpp):

• id, ts, e_kwh
• p_w, p1_w, p2_w, p3_w
• bat_v, bat_pct
• optional link fields: rssi, snr
• fault/reject fields: err_last, rx_reject, rx_reject_text (+ non-zero counters)

Home Assistant discovery is enabled (ENABLE_HA_DISCOVERY=true) and publishes config topics under:

• homeassistant/sensor/<device_id>/<key>/config

Web UI, Wi-Fi, Storage

• Wi-Fi/MQTT/NTP/web-auth config persists in Preferences (wifi_manager).
• AP fallback SSID prefix: DD3-Bridge-.
• Default web credentials: admin/admin.
• SD logging enabled (ENABLE_SD_LOGGING=true).

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:

~/.platformio/penv/bin/pio run -e lilygo-t3-v1-6-1

Test Mode

ENABLE_TEST_MODE replaces normal sender/receiver loops with dedicated test loops (src/test_mode.cpp). It sends/receives JSON test frames and publishes to smartmeter/<device_id>/test.