(kicad_sch (version 20230121) (generator eeschema)
  (uuid 743b8308-6a69-48de-a6ff-2336bc6c804f)
  (paper "A3")
  (title_block
    (title "PM_K-1 Core Board (brain) - VARASYS PolyMeter")
    (date "2026-05-30")
    (rev "A")
    (company "VARASYS")
    (comment 1 "Heirloom pro-audio modular core: RP2350 + +/-15V studio audio + balanced click-injector")
    (comment 2 "Design-of-record canvas - see hardware/DESIGN.md. Symbol placement + wiring = interactive TODO in Eeschema.")
  )
  (lib_symbols)
  (text "PM_K-1 CORE BOARD (\"brain\")\nHeirloom pro-audio modular core - design-of-record canvas.\nFull spec, BOM and interconnect pinouts: hardware/DESIGN.md + hardware/BOM.csv."
    (at 20 18 0)
    (effects (font (size 2.2 2.2)) (justify left top))
    (uuid 00109097-7760-4eb7-b299-bd3f64383aab)
  )
  (text "POWER TREE\nUSB-C 5V -> AP2112K 3V3 (digital IO)\nRP2350 internal SMPS -> 1.1V core (ext L)\nTPS65131 dual boost/inverter -> raw +/-18V\nTPS7A4901 / TPS7A3001 LDO -> CLEAN +/-15V (audio)\nStar ground; switcher in a guarded corner."
    (at 20 45 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid 4e184999-041e-4c11-9e86-faad487f2bad)
  )
  (text "MCU + DIGITAL\nRP2350A (QFN-60) - mind E9 erratum: external pulldowns on read inputs.\nW25Q128JV 16MB QSPI flash (wear-leveled).\n12MHz crystal. SWD 2x5 + labeled test points.\nI2S BCK/LRCK/DOUT + low-jitter 24.576MHz MCLK stay ON-CORE."
    (at 110 45 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid 43233868-23ee-43fa-b873-a47bffeacf5f)
  )
  (text "CLICK SOURCE\nPCM5102A I2S DAC (Burr-Brown).\nFed by dedicated low-jitter audio XO (ASEM1-24.576MHz),\nnot PIO-jittered MCLK."
    (at 200 45 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid a62ad51b-a1a9-4c34-b3d7-314c107afc7a)
  )
  (text "ANALOG INPUT (switchable line / instrument)\nProtection (non-negotiable): series DC-block film cap (blocks +48V phantom),\nclamp diodes/TVS to rails, series current-limit R.\nLINE: THAT1240 balanced receiver (laser-trimmed CMRR).\nINST: OPA1641 JFET Hi-Z buffer (>=1Mohm) + ~+10..15dB gain.\nK1 gold relay selects path (GPIO; touchscreen or optional face switch)."
    (at 20 80 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid 737ed14f-66db-4799-a337-21438143ce09)
  )
  (text "MIX + OUTPUT\nMix = digital/firmware (click level via DAC); analog stage at unity.\nTHAT1646 balanced driver + 47ohm build-out per leg.\nOutput level: Bourns 3296W 25-turn trim -> DAC FS = +4dBu (~+24dBu headroom).\nMUTE relay K2: fail-safe (de-energized = muted); HW supervisor, not MCU-dependent.\nGROUND-LIFT: face panel switch IN SERIES with core relay K3; soft-lift 100ohm||10nF.\nNO electrolytics in signal path - WIMA film caps, 0.1% thin-film R."
    (at 110 80 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid 99fe482f-1fde-4dd1-9579-56113dcb21bc)
  )
  (text "INDICATORS / MIDI / SPEAKER\nSIG/CLIP: peak detect -> LM393 -> RP2350 GPIO (UI) + LED lines on interconnect.\nMIDI: USB-MIDI default (firmware). DNP hardware option: H11L1 opto IN + 74LVC14 OUT/THRU.\nSpeaker: PAM8302 class-D, DNP per form factor.\nESD/EMI: USBLC6-2 on USB + CM choke; series R + ESD arrays on interconnect; ferrites at analog crossing."
    (at 20 120 0)
    (effects (font (size 1.6 1.6)) (justify left top))
    (uuid 03eeefa8-7728-4e14-90c0-6d0496a0d207)
  )
  (text "INTERCONNECTS (see DESIGN.md s7)\nJ2 DIGITAL RIBBON 2x13 - Pico-pinout-compatible (SPI/I2C/ADC/buttons/LED + GNDLIFT_SW/LINEINST_SW/SIG_LED/CLIP_LED).\nJ3 ANALOG 2x5 - AOUT H/C, AIN H/C, AGND, CHASSIS/SHIELD, SPK+/- (DNP). Kept away from the fast digital ribbon.\nJ4 MIDI 1x6 - OUT A/B, IN A/B, +5V, GND (only if DNP MIDI populated).\nRelays + I2S + MCLK are core-only and NOT on the ribbon; a Pico test brain drives digital I/O but not the analog chain."
    (at 110 120 0)
    (effects (font (size 1.5 1.5)) (justify left top))
    (uuid 0b1d2c3e-4f5a-6b7c-8d9e-0a1b2c3d4e5f)
  )
  (sheet_instances
    (path "/" (page "1"))
  )
)
