Preliminary architecture BOM for schematic capture and sourcing review. Quantities are per receiver. MPNs must be rechecked against current datasheets, distributor stock, lifecycle, module certification, and Flux footprint quality before purchase or PCB release.
Recommended Core ComponentsPower Input and ProtectionBuck Regulator Support ComponentsLogic, Reset and DecouplingRelay Drivers and IndicatorsField and RF ConnectorsTiming Components for External WatchdogMechanical and Assembly ItemsPreliminary Cost and Sourcing Notes
Relays, pluggable terminals, radio module, enclosure, and assembly labor are expected to dominate unit cost.
The detailed specification and BOM are now drafted. I found and corrected a critical inconsistency in the earlier notes: communications relays must be energized when healthy and use COM–NC so loss of receiver power produces an alarm.
Created the detailed Project Specification and Preliminary BOM, including architecture, fail-safe COM–NC communications alarms, power budget, interfaces, PCB/enclosure requirements, verification criteria, recommended MPNs, and alternatives. Remaining work is final datasheet/availability verification for the radio SKU, relays, power supply, antenna certification conditions, Siemens input module, and enclosure; further execution is paused because no ACUs are currently available.
The detailed architecture, preliminary power budget, interfaces, verification criteria, and open design selections are maintained in the Project Specification and Preliminary BOM project files.
Output Allocation
Reel 1 low
Reel 1 depleted
Reel 2 low
Reel 2 depleted
Reel 3 low
Reel 3 depleted
Reel 4 low
Reel 4 depleted
Transmitter A communications fault
Transmitter B communications fault
Relay Energization Logic
Reel/process outputs K1–K8: relay is normally de-energized; an alarm energizes the relay and closes COM-NO.
Communications outputs K9–K10: healthy state energizes the relay and opens COM-NC. Boot, reset, firmware lockup, missed external-watchdog service, unhealthy radio link, loss of 3.3 V logic, loss of 5 V coil power, or total receiver power loss de-energizes the relay and closes COM-NC to signal an alarm.
Firmware provides an independent recurring service pulse for each communications watchdog only while the corresponding transmitter link is healthy.
The receiver is an operational monitor and these outputs are not safety-rated.
Preliminary Power Result
5 V rail design peak: approximately 630 mA including ten relays, 3.3 V conversion, indicators, and margin.
5 V regulator target: at least 1.0 A, preferably 1.5 A with 60 V-class input tolerance.
3.3 V design peak: approximately 190 mA, dominated by LoRa transmit current.
3.3 V regulator target: at least 300 mA with thermal capability for approximately 0.32 W preliminary worst-case dissipation.