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  (paper "A3")
  (title_block
    (title "Fiber Dig-In Alarm — Cabinet Board Prototype (2-channel) — Top level")
    (date "2026-10-24")
    (rev "P1")
    (company "Prototype for engineering review")
    (comment 1 "Bench prototype: 2 optical TX (SFP) + 2 optical RX channels, MCU, power, alarm latch, relays")
    (comment 2 "Production board repeats the RX channel x8 and SFP slot x8 (see design spec)")
    (comment 3 "Generated schematic — verify custom/unfootprinted parts before layout"))
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  (text "12 V input, protection,\n3.3 V SFP buck, 5 V buck,\n3.3 V analog LDO"
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      (project "fiberalarm"
        (path "/13013f29-b9df-4b82-ad28-e51596b7e0b4"
          (page "3")))))
  (text "STM32G474 MCU,\ndecoupling, SWD,\nboot/reset"
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    (uuid "163f48dd-8f03-432b-a784-9635be067553")
    (property "Sheetname" "Optical TX"
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      (project "fiberalarm"
        (path "/13013f29-b9df-4b82-ad28-e51596b7e0b4"
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  (text "2x 1550 nm SFP transmitters,\nMSA power filters, status\npull-ups, test headers"
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    (uuid "da23f777-8323-4658-a0a2-0bcd56a9c4f4")
    (property "Sheetname" "Optical RX"
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      (project "fiberalarm"
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  (text "2x photodiode receive channels:\nTIA, comparator with hysteresis,\nwired-OR alarm, threshold DAC"
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    (uuid "9cffbfd6-80cf-4023-a6b9-c96bee0e0d7b")
    (property "Sheetname" "Alarm and I/O"
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  (text "Hardware alarm latch, relays,\nkey switch, CAL button, LEDs,\nUART and radio headers"
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    (uuid "aec94285-507e-477f-a2a3-8d93ca67abab"))
  (text "FIBER DIG-IN ALARM — CABINET BOARD, 2-CHANNEL BENCH PROTOTYPE\n\nLight from the far cabinet arrives on each received strand. Each photodiode channel compares its level\nwith a threshold set 3 dB below the calibrated level. Any channel below threshold pulls ALARM_N low,\nwhich latches the siren relay in hardware. The MCU logs the event, reports it by radio and clears the\nlatch only after the keyed reset. The two SFP lasers transmit continuously to the far cabinet.\n\nSheets: Power | MCU | Optical TX | Optical RX | Alarm and I/O\nProduction board: repeat the RX channel x8 and the SFP slot x8."
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