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Drogheda/03-Architecture-Hardware/2026-08-24_Drogheda_EinarBoard-v6_Phase-2_Schematic-Delta_v1.0.md

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title tags project author date status authority
EinarBoard v6 — Phase 2 — Schematic Delta (v5 → v6) — Build Spec
project-drogheda
hardware
einarboard
v6
schematic
kicad
gnss
4g
rf
delta
Project Drogheda Helgen CTO + Claude 2026-08-24 Active — THE schematic spec for v6. Every net/pin below is verified against the as-drawn `hbox-watchdog-v5.kicad_pcb` netlist (extracted 2026-08-24), not assumed. implements Phase 2 of `2026-08-24_…EinarBoard-v6_GNSS-4G-Integration_Design-Brief_v1.0.md`. Supplements `watchdog-electrical-design-state.md` (canonical) and `watchdog-production-schematic-delta.md` (the v3 precedent for this document's format).

EinarBoard v6 — Schematic Delta

Base: kicad/hbox-watchdog-v5 (EinarBoard 3.0 / v5.5, 15 pcs in fab since 22-Ago, git checkpoint c3e8e48). Target: kicad/hbox-watchdog-v6.

Method rules, unchanged and non-negotiable: file-level KiCad edits only (the MCP backend clobbered disk state on 24-Jul — read-only MCP queries are fine); git checkpoint after every block; every structural edit verified by an independent parse; %.10g coordinates; footprint rotation = R(−θ); zone refills in the GUI only.

⚠ Before starting: clear the stale .git/*.lock files and confirm the v5.5 fix commit actually landed. This has bitten two sessions running.

0. ⚠ Two corrections to the v6 brief, from the extracted netlist

The brief was written before the netlist was pulled. Both of these were wrong:

  1. "Spare PCF8574 pins" — there is only ONE. U13 (PCF8574T, SOIC-16 WIDE) has P0–P3 on /BATLED1–4, P4–P6 on /RGB_R/G/B. Only P7 (pin 12) and ~INT (pin 13) are free. All new control signals therefore go on MCU pins, of which there are plenty (§3).
  2. /MODEM_RST is not MCU-controlled today. It connects only J7.5 and SW4G1.1 (a pushbutton). The firmware has never been able to reset the modem in software — its only tool is killing SW_5V via PWR_CTRL. v6 fixes this (Block T).

A third finding worth recording: /3V3_MODEM is made by U7 (MP1584) → L7 → 3V3_MODEM, input /SW_5V. U7's job changes completely in v6 (§Block P).

1. Verified v5 baseline (extracted 2026-08-24)

1.1 STM32F411RET6 (U16) — as drawn

Pin Port Net Pin Port Net
2 PC13 /LED_C13 41 PA8 /CHRG_EN
8 PC0 /ETH_INT 42 PA9 /USART1_TX
14 PA0 /BAT_SENSE 43 PA10 /USART1_RX
15 PA1 /PWR_CTRL 44/45 PA11/12 /DFU_DM /DFU_DP
16 PA2 /GNSS_TX 46/49 PA13/14 /SWDIO /SWCLK
17 PA3 /GNSS_RX 50 PA15 /ETH_RST
20 PA4 /5V_SENSE 55 PB3 /CHRG_STAT
21 PA5 /IGN_SENSE 56 PB4 /CHRG_FAULT
22 PA6 /FAN_PWM 57 PB5 /BYP_CTRL
26 PB0 /EXT_LED 58/59 PB6/PB7 /I2C_SCL /I2C_SDA
27 PB1 /NTC_TEMP 61 PB8 /SER_IRQ
28 PB2 /BOOT1_STRAP 33–36 PB12–15 /ETH_CS/SCK/MISO/MOSI

Free (unconnected in v5): PC1, PC2, PC3, PC4, PC5, PC6, PC7, PC8, PC9, PC10, PC11, PC12, PD2, PA7, PB9, PB10 — 16 pins. USART6 = PC6/PC7 is free, which is what makes v6 possible without disturbing anything.

1.2 The three nets that carry the whole GNSS/4G architecture

Net v5 members Meaning
/USART1_RX U16.43 (PA10) · Rdfu1.1 (22k) · K1.1 (NC) · MOD1.23 (F9P TX2) receiver's UART2 uplink; MCU taps it passively
/DIN_4G K1.5/6 (COM) · J7.3 modem's data-in; fed from the relay
/DOUT_4G J7.2 · MOD1.17 (F9P RX2) RTCM downlink, hardwired, never switched

K1 (G5V-1 DC5): 1=NC=/USART1_RX · 5/6=COM=/DIN_4G · 10=NO=/USART1_TX (PA9) · 2=/SYS5V · 9=/KCOIL ← BYP_CTRL (PB5) via R40→Q6.

1.3 Power tree (verified)

P1.1 ─/24V_IN─┬─ D10 (SMBJ33A)
              └─ Q10 (IRFR5305, rev-pol) ──/24V── U2.7 (MP1584 fan buck) ──/SW_FAN─► 5V_FAN
P2.1 ─/VEH5V── RS1 (8 mΩ) ──/VIN_SW── U6.7 (LTC4040 VIN)
U6 (LTC4040) ──/MAIN5V── Q7 (AO4406A cutoff, gate /IGATE) ──/SYS5V── F1 (PPTC 3A)
                                                             ├─ U12 (MP1584) ─► /3V3_ETH
                                                             └─ K1.2 (relay coil supply)
/SW_IN ── Q1 (AO3401A, gate /GATE_LS ← PWR_CTRL) ──/SW_5V──┬─ MOD1.5   (shield 5 V)
                                                            └─ U7.2/7 (MP1584) ─L7─► /3V3_MODEM
U17 (AMS1117-3.3) ──/3V3

2. Deletions

Ref What Action
MOD1 simpleRTK2B Pro, Arduino UNO R3 socket, 32 pads @ (90.6, 129.9) DELETE — nets /GNSS_RX /GNSS_TX /DOUT_4G /USART1_RX /SW_5V re-terminate on U18
J7, J8 XBee 2.0 mm sockets, 10 pads each @ (174.2 / 196.5, 74.8) DELETE — nets re-terminate on U19
SW4G1 modem RESET pushbutton DELETE — replaced by MCU control (Block T)
Rmled1, MODEM_LED_A modem LED + resistor KEEP, re-source from the A7670SA NETLIGHT pin
MH7, MH9, MH10, MH11 shield / heatsink M2.5 bolt holes DELETE MH7/MH9/MH10; KEEP MH11 and add one partner near U19 for the modem heatsink clamp
U7, L7, C41, C43 the 3V3 modem buck REPURPOSE — see Block P

Do not delete K1. It is rewired (Block T), not removed — it is the fail-safe that keeps corrections flowing with a dead MCU.

3. MCU pin allocation — v6 additions

New net Pin Dir Function
/USART6_TX PC6 OUT MCU → modem (AT, GGA uplink, $PHLG) — via K1 NO
/USART6_RX PC7 IN modem → MCU (AT responses, RTCM tap)
/MODEM_PWRKEY PC8 OUT open-drain via Q20 (2N7002)
/MODEM_STATUS PC9 IN level-shifted 1.8 → 3.3 V
/MODEM_PWR_EN PC10 OUT enables U20 buck — the HARD_CYCLE path
/MODEM_RST PC11 OUT open-drain via Q21 (2N7002) — new MCU control
/GNSS_RESET_N PC12 OUT open-drain; U18 needs a 7–13 kΩ pull-up
/GNSS_ANT_DETECT PC1 IN antenna-open telemetry
/GNSS_ANT_SHORT_N PC2 IN antenna-short telemetry
/GNSS_TIMEPULSE PA7 IN TIM3_CH2 input capture

Unchanged: /GNSS_TX PA2 · /GNSS_RX PA3 (USART2, HardwareSerial GNSS(PA3, PA2)) · /USART1_RX PA10 (receiver UART2 tap) · /BYP_CTRL PB5 (K1 coil). Freed: PA9 — K1.10 moves to PC6. Leave PA9 as a test point. Still spare after v6: PC3, PC4, PC5, PB9, PB10, PD2, PA9 — 7 pins.

⚠ Verify no double-allocation with an independent netlist parse before ERC. That check is the reason this table exists.

Block N — GNSS island (U18)

Part: ZED-F9P-04B, 54-pin LGA 22.0 × 17.0 × 2.4 mm — LCSC C5120257, Extended. (Alternative under evaluation for v7: LG290P, 12.2 × 16 mm — see brief §1.4. Do not attempt a dual footprint; the pad rings overlap and the pin functions do not align.)

Signal Connect to Note
VCC /3V3_GNSS from U21 LDO only — never the shared /3V3
V_BCKP /3V3 via 1 kΩ + Schottky 45 µA hot-start; keeps ephemeris across a power-cycle
GND GND full pad-under-module via field
UART1 TX/RX /GNSS_RX / /GNSS_TX ⚠ net names are MCU-relative in this design: /GNSS_TX = MCU PA2 out → receiver RX
UART2 RX /DOUT_4G RTCM in — hardware path, unswitched
UART2 TX /USART1_RX uplink NMEA → K1.1 (NC) and PA10
RESET_N /GNSS_RESET_N 7–13 kΩ pull-up to /3V3_GNSS required
TIMEPULSE /GNSS_TIMEPULSE 4 mA drive
ANT_DETECT / ANT_SHORT_N /GNSS_ANT_DETECT / /GNSS_ANT_SHORT_N free antenna-fault telemetry — you have already lost H0005 and H0014 to antenna faults
VCC_RF Block S bias tee 50 mA typ / 300 mA abs max
D_SEL leave open (UART mode) open/high = UART; low = SPI
SAFEBOOT_N leave open
USB (V_USB, D+/D−) test pads only, not a connector u-center access at first article; 90 Ω pair, ESD if ever fitted

Decoupling: 100 nF per supply pin ≤ 2 mm, 10 µF + 1 µF bulk ≤ 10 mm, per the Capacitor-Placement-Map rules.

U21 — GNSS LDO

3.3 V, ≥ 300 mA, low noise. Candidates: TPS7A2033PDBVR (low-noise, preferred) or AP2112K-3.3TRG1 (cheap, LCSC C51118).

Input = /SW_5V, output = /3V3_GNSS — deliberately not the shared /3V3. Two reasons: the receiver stays on the MCU-gated stack rail, so PWR_CTRL (PA1 → Q1) still power-cycles it exactly as it does today; and an LDO fed from 5 V has ~1.7 V of headroom, which is what gives it the PSRR to reject the three MP1584 switchers this board carries. The ZED-F9P has no internal SAW — it will lock onto buck harmonics given the chance.

🔴 ZED-F9P VCC ramp rate ≤ 20 µs/V is a DAMAGE limit, not a guideline — 0 → 3.3 V in ≤ 66 µs. Most LDOs with soft-start are far slower. Measure the chosen LDO's rise time on the bench before fab. If it cannot meet it, add a fast load switch or a supervisor. This is a fab gate, not a nice-to-have.

Block O — LTE island (U19)

Part: A7670SA-LASC, 88-pin LGA 24 × 24 × 2.5 mm — LCSC C18548276, in the JLCPCB library, Extended, X-ray inspection required, MSL 3. ⚠ -SA only. -E/-C variants have no B4/B66 and will never attach on Telcel. ⚠ A7670 (88-LGA) ≠ A7672 (124 LCC+LGA) ≠ SIM7070 (68-LCC). Not interchangeable.

Signal Connect to Note
VBAT pins 55, 56, 57 /VBAT_MODEM all three, mandatory for RF performance. Trace/pour ≥ 3 mm
GND GND full via field
UART_TXD /DOUT_4G (level-shifted, Block R) → U18 UART2 RX and → /USART6_RX
UART_RXD /DIN_4G (level-shifted) ← K1 COM
PWRKEY /MODEM_PWRKEY_M via Q20 open-drain. Low ≥ 50 ms = on; ≥ 2.5 s = off. Internal 50 kΩ to VBAT. ≤ 100 nF total capacitance or you get spurious auto-power-on
RESET /MODEM_RST_M via Q21 open-drain, low 2–2.5 s. Same ≤ 100 nF rule
STATUS /MODEM_STATUS_M 1.8 V out; asserts ≈ 11.2 s after power-on
NETLIGHT Rmled1 → /MODEM_LED_A reuse the existing LED
VDD_1V8 /1V8_MODEM + 2.2 µF 50 mA max — level-shift reference ONLY, never a system rail
USIM1_* Block Q internal 4.7 kΩ pull-up on USIM1_DATA — no external needed
USB D+/D−, VBUS J9 (kept) 90 Ω pair. Reserve a USB_BOOT test pad — the only recovery if a firmware update bricks it. USB_BOOT must not be pulled low at power-up
RF_ANT (pin 60) Block S single antenna — Cat-1bis, no diversity port

Decoupling at the VBAT pins: 33 pF ∥ 10 pF ∥ 100 nF ∥ 1 µF ceramics, plus the Block P bulk.

Block P — modem 3.8 V rail (U20) — replaces U7's modem duty

Why this block exists, in one sentence: the 10-Ago fleet boot-loop was caused by exceeding the SD-15B's 3 A, and putting a 2 A LTE modem back on that same rail would recreate it.

/24V ──────────► D20 (SS34) ──┐
                              ├──/VIN_MODEM──► U20 (buck, 3.8 V) ──L20──► /VBAT_MODEM ──► U19
/MAIN5V ──► D21 (PMEG3050) ───┘                    ▲
                                                   │ EN
                                          /MODEM_PWR_EN (PC10)
Item Spec
U20 4.5–40 V in, ≥ 3 A, synchronous buck. Candidate: AP64350 class. ⚠ 40 V rating required — D10 (SMBJ33A) clamps at ~53 V, a 28 V part such as TPS54331 is not acceptable. NOT a fourth MP1584 — the existing three are the source of EMC findings 3 and 4
Output 3.8 V (mid-window of the A7670SA's 3.4–4.2 V)
D20 SS34 — already in the BOM (D2, D12). Drop irrelevant on the 24 V leg
D21 low-Vf Schottky (PMEG3050 class, Vf ≈ 0.35 V @ 2 A). In blackout MAIN5V ≈ 5 V → VIN_MODEM ≈ 4.65 V → duty ≈ 0.82. Verify U20's max duty covers it; if marginal, use a P-FET ideal diode (AO3401A, already in the BOM as Q1)
Bulk ≥ 470 µF low-ESR within 20 mm of the VBAT pins (spec floor is 300 µF; the extra is cheap insurance against the 2.8 A GSM burst)
Cin 1 µF + 10 µF within 3 mm of U20's VIN-GND — EMC finding 4, mandatory
Feedback divider at the FB pin, /FB_MODEM short and routed away from /SW_MODEM — EMC finding 3, mandatory
Enable /MODEM_PWR_EN (PC10). Power-cycle = EN low ≥ 2 s. Add a 1 kΩ bleed across the bulk so it actually collapses

Behaviour: cabinet live → modem's ~9.5 W comes from 24 V at ~0.45 A and the SD-15B never sees it. Blackout → same buck accepts MAIN5V (pack via LTC4040), unit keeps reporting (invariant #2).

U7 / L7 / C41 / C43 — disposition

/3V3_MODEM no longer feeds a modem. Repurpose U7 as the 3.3 V supply for the level shifters and the LTE-island logic, renaming the net /3V3_LTE, or delete U7/L7/ C41/C43 entirely and take that logic from /3V3. Decide before routing the 3V3 tree — this is the same open decision that was left dangling on U12/L8 in the 3.0 brief, and it should not be left dangling twice. Recommendation: delete, feed from /3V3; the shifters draw milliamps.

🔴 Also fix in this block

The LTC4040 input-limit errata. RS1 (8 mΩ) sets a 3.12 A input limit above the SD-15B-05's 3 A rating. Bring the limit below the PSU rating, or specify a larger PSU. This has been a standing errata since 10-Ago. v6 is where it gets fixed.

Block Q — MFF2 SIM (U22)

Item Spec
Package MFF2 / DFN-8 5 × 6 mm (SON-8)
Signals USIM1_VDD · USIM1_CLK · USIM1_DATA · USIM1_RST · GND
Pull-ups none — U19 has an internal 4.7 kΩ on USIM1_DATA
Voltage 1.8 V / 3.0 V auto-detect, no strapping
ESD array at the SIM lines (ESDA6V1W5 / SMF15C class)
Placement ≤ 20 mm from U19, short matched-ish traces, GND guard

⚠ Sourcing is a lead-time item, not an engineering task. You need a real Telcel/AT&T MX or Mexican-profile MVNO MFF2. Flat-rate sensor IoT SIMs (500 MB / 10 years) are an order of magnitude too small for 50–200 MB/month. Start this in Phase 0.

Block R — level translation (U23, U24)

A7670SA I/O is 1.8 V. The STM32's V_IH ≈ 2.31 V — 1.8 V will not read as HIGH.

Line Direction Method
/DIN_4G (MCU/K1 → modem RX) 3.3 → 1.8 SN74LVC2T45DCUR, DIR fixed
/DOUT_4G (modem TX → MCU + receiver) 1.8 → 3.3 SN74LVC2T45DCUR, DIR fixed
/MODEM_STATUS 1.8 → 3.3 same device, 2nd channel
/MODEM_PWRKEY, /MODEM_RST 3.3 → open-drain Q20, Q21 = 2N7002. Not through a shifter — MCU absent must leave them unasserted
  • VccA = /1V8_MODEM (from U19's VDD_1V8, 2.2 µF); VccB = /3V3.
  • Prefer direction-fixed 74LVC2T45 over auto-direction TXS0108E — auto-direction parts misbehave against strong drivers and multi-load nets, and /DOUT_4G drives two loads.
  • ⚠ The RTCM path passes through U24. Add DNP 0 Ω bypass footprints across it so a suspect shifter can be jumpered out at bring-up.
  • /DOUT_4G fan-out on the 3.3 V side: U18 UART2 RX and /USART6_RX (PC7) through a 100 Ω series resistor for isolation.

Block S — RF front ends

Stackup (unchanged topology, new requirement)

F.Cu signal + GND pour · In1 solid GND · In2 3V3 plane · B.Cu signal + GND pour. ✔

New: order as controlled impedance. JLCPCB 4-layer JLC04161H-7628, F.Cu→In1 prepreg ≈ 0.2104 mm. Target 50 Ω CPWG on F.Cu referenced to In1 — roughly 0.35 mm trace / 0.25 mm gap at εr ≈ 4.4. Confirm with JLCPCB's own impedance calculator before layout, not after.

Rules for both RF traces, no exceptions: referenced to an unbroken In1 (no plane split, no In2 island underneath), as short and straight as possible, ground-stitched both sides at ≤ λ/20, nothing crossing on any layer.

S1 — GNSS (J12)

J12 (U.FL) ─╥─ C_DC (100 nF) ─── U18.RF_IN
            ║
            └─ L_BIAS (≥68 nH 0603, SRF > 1.6 GHz) ─┬─ 100 nF ∥ 100 pF ─ GND
                                                     └─ VCC_RF (U18)
   D_ESD (>2 GHz rated, <0.5 pF) at J12

Active antenna is mandatory — the ZED-F9P has no internal LNA.

S2 — LTE (J13)

U19.RF_ANT ─── π-match pads (series 0402 + 2× shunt 0402, series = 0 Ω default)
           ─── J13 (U.FL) ─── D_ESD (low-cap <0.5 pF)

S3 — 🔴 GNSS desense — the #1 technical risk

A 23 dBm transmitter drawing 2–3 A bursts next to a GNSS front end is a classic RTK-killer. The Ardusimple shield has been hiding this. A bare module hands it to you.

  1. Board separation: U18 in the freed MOD1 area (bottom-left), U19 in the freed XBee area (right edge) → ≈ 149 mm apart, the full diagonal. The GNSS corner is also the furthest point from all four switchers (nearest, U7 at 140.0/112.9, ~60 mm).
  2. Antenna separation ≥ 20 cm on the enclosure — two bulkheads. Design rule, not an optimization.
  3. Modem return path routed away from the GNSS island; no shared reference but In1.
  4. No 1575 SAW — it would kill L2 on a dual-band receiver. Specify an active antenna with good out-of-band rejection instead.
  5. Measured at gate G3 (Phase 6): fix quality and C/N₀ with the modem idle vs. transmitting at full power. Pass/fail, not opinion.

S4 — ESD everywhere (EMC finding 5)

Every external connector gets a clamp within 10 mm. D14/D15/D16 move from the MCU to within 10 mm of J11. J9 gets the ESD array it never had (< 2 pF on the data lines). J12, J13, P1, P4, P15, P16 all get appropriate clamps.

Block T — K1 rewiring (one net change, big consequence)

K1 pin v5 v6
1 (NC) /USART1_RX unchanged — receiver UART2 TX
5/6 (COM) /DIN_4G unchanged — modem RX
10 (NO) /USART1_TX (PA9) /USART6_TX (PC6) ← the only change
2 /SYS5V unchanged
9 /KCOIL ← BYP_CTRL (PB5) unchanged

What this buys. Energised (normal operation) the MCU owns the modem's RX line: it can send AT commands, forward the receiver's GGA byte-exact, and inject $PHLG. De-energised — MCU dead or absent — the relay relaxes and the receiver's own GGA goes straight to the modem, so corrections keep flowing. Invariants #2 and #3 both hold, with hardware, for the price of one moved net.

Consequence to state plainly: v6 makes Modo B the normal operating mode. Consistent with the EPCT decision already on record.

4. New net list

Net Members
/3V3_GNSS U21.out · U18.VCC · decoupling
/VBAT_MODEM L20.2 · U19.55/56/57 · bulk + ceramics
/VIN_MODEM D20.k · D21.k · U20.VIN · Cin
/1V8_MODEM U19.VDD_1V8 · U23.VccA · U24.VccA · 2.2 µF
/USART6_TX U16.37 (PC6) · K1.10
/USART6_RX U16.38 (PC7) · 100 Ω → /DOUT_4G (3.3 V side)
/MODEM_PWRKEY / _M U16.39 (PC8) → Q20 → U19.PWRKEY
/MODEM_STATUS / _M U19.STATUS → U24 → U16.40 (PC9)
/MODEM_PWR_EN U16.51 (PC10) · U20.EN
/MODEM_RST / _M U16.52 (PC11) → Q21 → U19.RESET
/GNSS_RESET_N U16.53 (PC12) · U18.RESET_N · 10 kΩ pull-up
/GNSS_ANT_DETECT U16.9 (PC1) · U18.ANT_DETECT
/GNSS_ANT_SHORT_N U16.10 (PC2) · U18.ANT_SHORT_N
/GNSS_TIMEPULSE U16.23 (PA7) · U18.TIMEPULSE
/SIM_VDD /SIM_CLK /SIM_DATA /SIM_RST U19 ↔ U22
/RF_GNSS /RF_LTE 50 Ω, own netclass, no autorouting

Changed: /DOUT_4G gains U18.UART2_RX, U24 and the PC7 tap; loses J7.2, MOD1.17. /DIN_4G gains U23/U19; loses J7.3. /USART1_RX loses MOD1.23, gains U18.UART2_TX. /USART1_TX loses K1.10 → PA9 becomes a test point.

Netclasses: keep HV24; add RF (50 Ω, no auto-route) and PWR_MODEM (/VBAT_MODEM, /VIN_MODEM — min width 1.5 mm, target ≥ 3 mm).

5. Inherited EMC fixes — schematic-level, day-one

# Fix Where it lands in the schematic
🔴 1 /SW_BAT ≥ 2 mm polygon netclass + layout; load-bearing — blackout now feeds the modem too
🔴 2 /BAT_PLUS ≥ 1.5 mm + via farm same
🟠 3 R20/R21 at U2 pin 4, /FB_FAN short schematic grouping so layout can honour it
🟠 4 1 µF + 10 µF ≤ 3 mm of every buck VIN — including U20 add the parts now
🟠 5 ESD < 10 mm of every external connector Block S4
🟡 6 Crystals → 3225 package, < 5 mm (Y1, Y3, Y4 are HC-49 at 12–15 mm) change footprints in the schematic pass
🟡 7 ETH RX pair coupled and length-matched layout, flagged here
🟡 8 Fill the 8 empty 20 mm stitching cells free — most were under MOD1

6. Part additions

Ref Part LCSC Note
U18 ZED-F9P-04B C5120257 Extended, X-ray, ~104–129 in stock — consign from Mouser for ≥ 100 units
U19 A7670SA-LASC C18548276 Extended, X-ray, MSL 3, 220 in stock
U20 40 V / 3 A sync buck (AP64350 class) verify 40 V minimum
U21 TPS7A2033 or AP2112K-3.3 C51118 (AP2112K) ⚠ verify the ≤ 66 µs ramp
U22 MFF2 SIM carrier lead-time item
U23, U24 SN74LVC2T45DCUR verify direction-fixed
Q20, Q21 2N7002 verify open-drain PWRKEY / RESET
D20 SS34 in BOM (D2) 24 V leg
D21 PMEG3050 class verify low-Vf, 5 V leg
J12, J13 U.FL / IPEX MHF1 SMT receptacle verify + 2 pigtails, 2 SMA bulkheads
L20 buck inductor per U20's datasheet verify ≥ 4 A saturation
— 2× 220 µF low-ESR + ceramics verify Block P bulk
— ESD arrays, RF ESD, bias-tee L/C, π-match 0402s verify Blocks S1–S4

All "verify" rows must be confirmed against the live JLCPCB library at upload, not from a cached DB. The v4-bom.xls labels are on record as unreliable; check pin-counts vs pad-counts every time.

7. Execution order & verification

Step Work Check
T0 Clear stale .git/*.lock; confirm the v5.5 fix commit landed; branch v6 from c3e8e48; copy v5 → hbox-watchdog-v6 parse-verify the copy opens clean
T1 Deletions (§2) netlist parse: MOD1/J7/J8/SW4G1 gone, no orphan nets
T2 Block T (K1.10 → PC6) 1-net diff, nothing else moved
T3 Block N + U21 ERC on the GNSS island alone
T4 Block O + Block Q + Block R ERC; confirm every 1.8 V line crosses a shifter
T5 Block P + LTC4040 input-limit fix recompute the backup power budget vs the 1S4P ~12 Ah pack
T6 Block S (RF + ESD) + netclasses RF netclass exists and is excluded from autorouting
T7 EMC list §5 each row ticked individually
T8 Full ERC + independent pin-map parse ERC 0; no double-allocated MCU pin

Gate G2: ERC 0 plus an external review of the RF and power sections. This is Helgen's first RF design — do not let ERC-clean stand in for reviewed.

8. What is deliberately NOT in v6

  • A second GNSS footprint. LG290P's pads overlap the F9P ring and the functions don't align. The cost-down is a v7 respin of one corner — which is exactly why Block N is an island.
  • A modem mezzanine daughtercard. Rejected with "full integration" (brief §0); revisit only if gate T1's cabinet temperature forces the industrial tier.
  • eUICC. MFF2 only, per the 24-Ago decision.
  • Cat-4 / WCDMA. See brief §2.3.

9. Cross-references

  • v6 brief: 2026-08-24_Drogheda_EinarBoard-v6_GNSS-4G-Integration_Design-Brief_v1.0.md
  • Phase 1 firmware: 2026-08-24_Drogheda_EinarBoard-v6_Phase-1_NTRIP-Firmware-Spec_v1.0.md
  • EMC fix list: 2026-08-22_Drogheda_EinarBoard-v5_EMC-Audit_v1.0.md
  • Canonical electrical state: watchdog-electrical-design-state.md
  • Format precedent: watchdog-production-schematic-delta.md
  • Cap placement rules: 2026-08-14_Drogheda_EinarBoard-3.0_Capacitor-Placement-Map_v1.0.md
  • Invariants: #1 power-off safe (Q20/Q21 open-drain, buck EN default off) · #2 never vanish (Block P dual input, Block T fail-safe) · #3 power-cycle recovery (MODEM_PWR_EN) · #5 no head-of-line blocking · #6 no secrets