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Reference Hardware Design — Field Data Acquisition

PV Edge Node: From Modbus Field to Cloud

Important framing: this is not the actual internal architecture of NextWave's PVPulse / TotalPulse platform — I don't have access to that. Instead, this is an engineering reference design grounded in the knowledge areas the posted role calls for (Modbus/RS-485 field data acquisition, the SunSpec data model, cloud-based monitoring, data-loss prevention), backed by public datalogger literature and real component pricing. It's meant as a concrete answer to "how would you think about a system like this" in the interview — NextWave's actual supplier and part choices will differ.

01Show what actually changes

Systems without sufficient local buffering may lose telemetry during connectivity outages. That's the one real difference the proposed design makes.

BEFORE — no buffering Inverter / Meter (Modbus RTU) RS-485 Simple Datalogger local logging, no buffer if connection drops: telemetry may be lost Cloud / Monitoring (data with gaps) PROPOSED — edge node with local buffering Inverter / Meter (Modbus RTU) RS-485 Edge Data Node ESP32-S3 + isolated RS-485 + cellular modem MQTT / HTTPS + TLS Cloud / Monitoring (continuous, ordered data) Local Buffer (≥7 days, flash/SD) written here while offline, sent in order once reconnected
Figure 1 — Systems without sufficient local buffering may lose telemetry during connectivity outages; in the proposed design, the edge node holds data locally and automatically backfills once the connection returns.

02Inside the node: isolation and data path

The one physical boundary between the outdoor field side (exposed to voltage transients) and the electronics is the isolation barrier.

outdoor / field side RS-485 Line A/B signal galvanic isolation Isolated Transceiver ADM2483 Modbus frame MCU + RTC ESP32-S3 timestamps via DS3231 record Local Buffer SD/flash, ≥7 days held here while offline if connected: flush in order Cellular Modem LTE Cat-4 encrypts via TLS MQTT ☁ inside sealed (IP65) enclosure →
Figure 2 — The field signal first crosses the isolation barrier; the MCU timestamps every record, the local buffer holds data while offline, and flushes it in order once the connection returns.

03Protocol and resilience decisions

Data model

  • Modbus RTU (RS-485), 1–10 sec sampling interval
  • SunSpec Alliance register map — vendor-independent reading
  • Cloud publishing via MQTT over TLS (or HTTPS)
  • Optional: Ethernet (W5500) as a backup path if a site PC is present

Data-loss prevention

  • ≥7 days of local buffering (flash/SD), automatic backfill on reconnect
  • Battery-backed RTC — records keep the correct timestamp
  • Signed OTA updates, TLS-encrypted transport
  • IP65 enclosure, −25°C to +70°C operating range, surge protection

04Bill of materials (single unit, approximate)

Only one line item is confirmed against a live supplier price; the rest are engineering estimates based on current market ranges — not a formal quote.

ComponentExample partQtyUnit $SubtotalSource
MCU / Modbus masterESP32-S3-DevKitC-1110.0010.00estimate
Isolated RS-485 transceiverADM2483BRWZ-REEL15.615.61LCSC
Cellular modem (LTE Cat-4)Quectel EC25 + antenna130.0030.00estimate, $25–35 range
RTC module (battery-backed)DS3231 breakout13.003.00estimate
Industrial microSD (8GB) + holderSanDisk/InnoDisk Industrial112.0012.00estimate
Backup batteryLiFePO4 3.2V ~1500mAh18.008.00estimate
Power stage + surge protectionDC-DC buck + TVS set18.008.00estimate
EnclosureIP65, DIN rail, ~150×110mm120.0020.00estimate
PCB fab + assembly + connectorslow qty / prototype1 set32.0032.00estimate
Single unit, prototype qty≈ 128.61

At a run of 50–100 units, volume discounts on PCB/assembly and the modem are expected; a unit cost landing around $70–90 is a reasonable engineering estimate. In addition, a cellular IoT SIM data plan typically runs about $2–6/month per device for low-volume periodic data — not included in this hardware list.