IoT Fire Alarm Device Design

flux

You should ask Quectel / supplier for the EC25MXGA hardware design package, not just the marketing datasheet.
Ask for:
  1. EC25MXGA Hardware Design Guide
    • Full pin descriptions
    • Power supply requirements
    • PWRKEY / RESET timing
    • UART / USB / SIM / RF reference circuits
    • VDD_SDIO usage guidance
  2. Recommended PCB land pattern / footprint
    • Pad dimensions
    • Pad numbering
    • Paste mask / solder mask recommendations
    • Keepout zones under/around the module
    • Assembly notes
  3. Reference schematic
    • VBAT_RF / VBAT_BB decoupling
    • SIM socket wiring
    • Antenna matching / ESD
    • Status pins
    • Power-on/off sequence
  4. RF layout guidelines
    • 50 Ω antenna routing
    • Ground stitching via recommendations
    • Antenna connector/matching network placement
    • Diversity/GNSS pins if used or unused
  5. Certification documents
    • RCM / ACMA / AS/CA S042 relevance
    • Carrier approval info for Australia
    • LTE band support for AU carriers
    • Test reports if available
  6. Lifecycle / supply confirmation
    • Active production status
    • Recommended replacement if EC25MXGA is not preferred
    • Minimum order / lead time
Short message you can send:
We are designing a dual-modem Australian fire alarm signalling device using 2 × EC25MXGA. Please provide the EC25MXGA hardware design guide, recommended PCB land pattern/footprint, reference schematic, RF layout guide, SIM interface recommendations, VDD_SDIO connection guidance, Australian carrier/certification documentation, and lifecycle/supply status.
drewmoutney

drewmoutney

Ok I’ll contact them

flux

Good plan. Ask them specifically for the hardware design guide + recommended PCB land pattern for EC25MXGA-128-SNNS.
Until we get that, the safest path is:
  • Keep EC25MXGA in the design.
  • Do not send the PCB to manufacture yet.
  • Continue with placement/routing cleanup only as a draft.
  • Finalize modem footprint, SIM wiring, RF layout, and VDD_SDIO treatment once Quectel confirms the official guidance.
Clean draft layout
Review EC25 wiring
Check power budget
Update factory checklist
Run current checks
Sign up to send

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AS1670.3 / AS4428.6 / Romteck Grid Design Notes
Sources used
  • User-uploaded AS1670.3 PDF, OCR-extracted. Critical values must be verified against the official current standard.
  • Romteck Grid website: https://www.romteckgrid.com.au/
  • Public search results for AS4428.6 overview and Romteck/ASE context.
User-added requirement
  • Device input operating voltage range: 12–24 VDC.
AS1670.3 implications for this project
AS1670.3 is focused on fire alarm monitoring from the Alarm Signalling Equipment (ASE) through the monitoring network to the monitoring centre / fire dispatch path.
Key design implications:
  • The product should be treated as ASE or ASE-adjacent equipment.
  • Alarm transfer performance target: alarm input to ASE through acknowledgement by fire dispatch centre must support the AS1670.3 transfer-time requirement. The uploaded draft states ≤20 s from alarm signal input to ASE to fire dispatch acknowledgement under specified simultaneous/sequential alarm conditions.
  • Telecommunications path loss must be indicated at both the monitored site and monitoring centre within 90 s.
  • Individual monitored site network reliability target in the uploaded draft: not less than 0.99.
  • Aggregate monitoring network reliability target in the uploaded draft: not less than 0.9995.
  • Clock/time stamping must be synchronized within 1 minute where ASE time clocks are used.
  • Alarm, fault, isolate, test, and network-fault events need to be received, processed, timestamped, logged, and acknowledged by the monitoring environment.
  • Appendix C references AS4418.2-style behavior: initialization, cyclic transmission/heartbeat, event-initiated reporting, clock synchronization, remote testing, buffering of events during link failure, and link-failure reporting.
AS4428.6 implications
AS4428.6 is the Australian Standard specifically covering Alarm Signalling Equipment. Public references indicate the 2024 edition specifies minimum equipment requirements, functions, performance criteria, and test expectations for ASE used with automatic fire detection and alarm systems.
For this design, AS4428.6 should drive the ASE hardware/function requirements, while AS1670.3 should drive the monitoring network/system performance requirements.
Expected schematic-level implications:
  • Dedicated alarm/fault/isolate/test input processing from the fire panel/CIE.
  • Clear local indication of power, alarm, fault, isolate/test, and communication-path state.
  • Secure service/test mode handling.
  • Reliable nonvolatile event storage or buffered event queue for communication outages.
  • Watchdog/supervisor circuitry for MCU and modem subsystem.
  • Hardware fault detection for power rails, modem status, SIM presence, antenna/RF path status where practical, and field input line state.
  • Robust surge/ESD protection on field wiring, SIM, USB-C, antenna, and external power.
Romteck Grid context
Romteck Grid is an Australian automatic fire alarm monitoring provider. Their site highlights:
  • Alarm Signalling Equipment designed/manufactured in Perth.
  • 4G dual-SIM capability.
  • Earlier support for 3G/4G/Cat-M1/NB-type cellular capability.
  • 24/7 monitoring centre support.
  • Fire monitoring services for NSW, ACT, and Victoria contexts.
  • ACMA and ActivFire certification context.
Design implications if aiming for Romteck-like compatibility:
  • Do not depend on 3G.
  • Prefer 4G LTE and ideally LTE-M/Cat-M1-capable modem options where service coverage and certification permit.
  • Dual SIM is appropriate, but we need to decide whether the architecture is one SIM per modem or multiple SIMs switchable per modem.
  • The communication firmware must support supervised heartbeat/cyclic reporting, event-initiated alarm reporting, acknowledgement handling, retry, buffering, and link-failure detection within 90 s.
  • The final product will need ACMA/radio compliance planning and likely fire-system listing/recognition such as ActivFire depending on market path.
Hardware architecture decisions based on the above
Recommended baseline:
  1. 12–24 VDC protected input stage.
  2. Reverse-polarity, surge, EFT, ESD, fuse/current-limit, and brownout protection.
  3. High-efficiency buck to system intermediate rail.
  4. Separate high-peak-current modem supply domains for each Quectel module.
  5. STM32H757 logic rails with sequencing/supervision.
  6. RTC/time reference and backup strategy for timestamping.
  7. Nonvolatile memory for event queue and configuration.
  8. Eight supervised inputs with configurable EOL resistor interpretation if connecting to CIE/field circuits.
  9. Local indicators and LCD UI for communication fault, alarm state, test/isolate mode, power fault, and service status.
  10. Service/debug USB-C separated from certified field wiring functions unless formally required.
Major open requirements
  • Confirm whether the product is intended to be certified directly as AS4428.6 ASE.
  • Confirm whether the current applicable standards are AS1670.3:2024 and AS4428.6:2024.
  • Confirm target monitoring centre/protocol: Romteck-compatible, AS4418.2, proprietary API, MQTT/IP, or another fire-dispatch-approved protocol.
  • Confirm whether dual Quectel EC21-AUV remains mandatory, or whether a newer LTE-M/4G module is acceptable.
  • Confirm if 12–24 VDC is nominal only or if the design must survive wider fire-panel supply tolerance, reverse polarity, surges, and battery charger transients.
  • Confirm required backup power runtime for the field ASE device, not only the monitoring centre.
  • Confirm eight input electrical behavior: dry contact, relay outputs from CIE, supervised EOL, voltage inputs, Class A/B wiring, or mixed.
  • Confirm required local indicators, buzzer, tamper switch, cabinet door switch, and test/isolate key behavior.
Next schematic action
Start with the power/input protection and communications supervision architecture, not the MCU pinout. The compliance-driven requirements make power integrity, link supervision, event buffering, and fault annunciation first-order design constraints.

  • Sources used

  • User-added requirement

  • AS1670.3 implications for this project

  • AS4428.6 implications

  • Romteck Grid context

  • Hardware architecture decisions based on the above

  • Major open requirements

  • Next schematic action