Wearable BCI Design Discussion
Thought
Work done
- SWD programming: verified existing 2x3 SWD header PROG is wired to U3 on nets SWDIO, SWDCLK, 3V3_D, and GND.
- BQ25895 support: added the required 47 nF BTST bootstrap cap C5 between U4 BTST and SW; verified the JST-PH 2-pin battery connector J4 is connected to BAT and GND; verified SYS from U4 feeds both LDO1 IN and LDO2 IN.
- Dual-LDO isolation: ensured LDO1 serves the 3V3_D rail (MCU/USB) and LDO2 serves the 3V3_A rail (analog); connected 3V3_A to U2 AVDD1 and added C6 (SYS input decoupling) and C7 (3V3_A output decoupling).
Placement prep (manual guidance)
- Quiet Zone (9:00): place J1 on the left edge; put D1/D2 between J1 and U2; place U2 immediately to the right of J1.
- Noisy Zone (3:00): place J2 top-right; place U4 + L1 just below J2; place battery connector J4 adjacent to U4.
- Bridge Zone (6:00): place U3 bottom-center/right; place PROG along the bottom edge.
- Decoupling proximity rule: move each IC’s local decouplers (e.g., C5, C6, C7, C1, C2) to be as close as physically possible to the corresponding power pins.
Routing handoff (deferred)
- Plan: bottom-layer GND pour; top-layer 0.5 mm power trunk; keep top-layer sensor inputs as short as possible; route SPI on bottom layer.
Success criteria review
- ✅ SWD header added/connected to U3
- ✅ BQ25895 improvements implemented: C5, J4, SYS->both LDOs
- ✅ Dual-LDO isolation implemented with distinct 3V3_D and 3V3_A
- ✅ Placement-zone guidance provided (Quiet/Noisy/Bridge) + decoupling proximity guidance
- ✅ Routing guidance documented; routing intentionally deferred
Next steps
- I cannot auto-place or auto-route. After you place parts, run Auto-Layout for routing and I will re-check airwires/DRC and iterate placement tweaks if needed.
