sistemas-cibernetico-fisicos/hardware/v2.8/README.md

PCB v2.8 Hardware Reference

Last updated: 2026-07-15 Source: EasyEDA Pro project Savearth GBT.eprj + firmware bsp_v28.c

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Component Map

Active ICs

Ref	Symbol	Part	Function
U3	ESP32-S3-WROOM-1-N8R8	ESPRESSIF	Main MCU, 8MB flash, 8MB PSRAM
U11	BQ25895RTWR	TI	Battery charger/monitor, I2C 0x6A
U12	PCAL9538ABSHP	NXP	8-bit I/O expander, I2C 0x70
U9	MIC94073YMT-TR	MICROCHIP	P-channel load switch (PWR_EN → SW_3.3V)
U2	AP2112K-3.3TRG1	DIODES	3.3V LDO regulator (ESP32 always-on rail)
U5	ICS-43434	TDK InvenSense	MEMS microphone, I2S
U14	DW01	SHIKUES	Battery protection IC

Discrete Semiconductors

Ref	Symbol	Part	Function
Q2	Si2302CDS-T1-E3-HXY	HXY	N-MOSFET (load switch)
Q4	AO3400A	YTL	N-MOSFET
Q5	AO3400A	YTL	N-MOSFET
D1	LESD5D5.0CT1G	KUU	TVS/ESD protection
D2	LESD5D5.0CT1G	KUU	TVS/ESD protection
D3	LESD5D5.0CT1G	KUU	TVS/ESD protection
D5	BAT760-7	DIODES	Schottky diode
D6	BAT760-7	DIODES	Schottky diode
D7	BAS16HT1G	onsemi	Switching diode
D9	VSKY10201406-G4-08	VISHAY	Schottky diode
D10	V8PAN50-M3/I	VISHAY	Schottky diode

Passives (selected)

Ref	Symbol	Value	Function
R23	0402WGF1002TCE	10kΩ	GPIO0 pull-up to 3.3V
R19	0402WGF100JTCE	10Ω	Series resistor
R26	0402WGF220JTCE	22Ω	Series resistor
R27	0402WGF220JTCE	22Ω	Series resistor
R28	1206W4F1004T5E	1MΩ	High-value resistor
R37	CRCW04020000Z0ED	0Ω	Jumper
R43	CRCW04025K23FKED	5.23kΩ	Precision resistor
R44	CRCW040230K1FKED	30.1kΩ	Precision resistor
R45	CRCW040210K0FKED	10kΩ	Resistor
R46	CL0402FN33RP	33Ω	Series resistor
R50	HOT1206-2W-0R	0Ω	Jumper (high current)
C17	1206B103K202NT	10nF 2kV	High-voltage cap (USB protection)
L3	IHLP2020BZER2R2M11	2.2µH	Power inductor

Connectors

Ref	Symbol	Part	Function
USB1	HYCW396-USBC16-712B	USB-C	USB Type-C connector
CN1	HC-FPC-0.5-40P-FH20	FPC 40-pin	LCD ribbon connector
CON_BAT	S3B-PH-SM4-TB	JST PH 2-pin	Battery connector
FlashPort	HX PZ1.27-1x6P	Pin header 6-pin	Debug/flash header
RS1	59170-1-S-00-D	Littelfuse	Reed switch (magnet sensor)
SW2	SS12D00G3	Slide switch	Power switch
PIR1	AMD312	PIR sensor	Motion detection
NTC	103AT-2	NTC thermistor	Temperature sensing

FlashPort Pinout (6-pin debug header)

Pin	Net	Connection	Notes
1	+3.3V	Power rail	3.3V supply
2	EN	U3 pin 3 (EN)	Chip enable (active high)
3	TX0_AP_BTN	U3 pin 37 (TXD0)	UART0 TX
4	RX0_EN_REG3.3	U3 pin 36 (RXD0)	ERRATA: The problematic wire
5	IO0_LCD_RST	U3 pin 27 (IO0)	GPIO0 boot strap
6	GND	Ground	Reference

Warning: Pin 4 (RX0_EN_REG3.3) was the net that created the v2.8 root cause. On affected boards, this pin had a physical wire to VSYS that injected noise.

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Power Rail Topology

VBUS (USB 5V)
    │
    ├──→ D10 (V8PAN50) ──→ USB protection
    ├──→ C17 (10nF 2kV) ──→ EMI filter
    │
    ▼
┌─────────────────────────────────────────────┐
│  U11: BQ25895RTWR (I2C 0x6A)              │
│  IN+ = VBUS                                │
│  BAT = Li-Ion cell (via CON_BAT)           │
│  SYS = VSYS (switched output)              │
│  PMID = VBUS decoupling                    │
│  REGN = internal LDO (charge pump)         │
│  SW = switching node (inductor L3)         │
└──────┬──────────────────┬───────────────────┘
       │ VSYS             │ VBAT
       │                  ▼
       │            ┌──────────┐
       │            │ Battery  │
       │            │ Li-Ion   │
       │            └──────────┘
       │
       ▼
┌──────────────────────────────────┐
│  U9: MIC94073 (load switch)     │
│  IN  = VSYS                     │
│  EN  = PWR_EN (GPIO1)          │
│  OUT = SW_3.3V                  │
└──────────┬───────────────────────┘
           │ SW_3.3V
           ▼
    ┌──────┴──────┐
    │             │
    ▼             ▼
┌────────┐  ┌────────────────┐
│ST7701S │  │  PCAL9538A     │
│ (LCD)  │  │  IO Expander   │
└────────┘  └────────────────┘

U2: AP2112K-3.3 ──→ 3.3V always-on rail (ESP32-S3 VDD)
    IN = VSYS (always powered)
    OUT = 3.3V (ESP32 core, I2C, flash)

Rail Summary

Rail	Source	Voltage	Loads	Control
VBUS	USB-C	5V	BQ25895 input	USB connector
VBAT	Li-Ion	3.0-4.2V	BQ25895 battery port	Charge/discharge
VSYS	BQ25895	3.0-4.5V	System supply	BQ25895 internal
SW_3.3V	MIC94073	3.3V	LCD, IO expander, PIR	GPIO1 (PWR_EN)
3.3V	AP2112K	3.3V	ESP32-S3, I2C, flash	Always on

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GPIO Pin Map (from firmware)

Direct GPIO Connections

GPIO	Function	Net	Component
0	LCD_RST / Boot strap	IO0_LCD_RST	ST7701S reset
1	PWR_EN	PWR_EN	MIC94073 enable
2	I2S_MIC_LRCL	WS	Microphone
3	LCD_R2	R2	ST7701S RGB
4	LCD_PCLK	LCD_PCLK	ST7701S clock
5	LCD_B1	B1	ST7701S RGB
6	LCD_BACKLIGHT	BL_PWM	ST7701S backlight
7	LCD_SPI_SCL	LCD_SCK	ST7701S SPI
8	IOEXP_A0	A0	PCAL9538A address
9	LCD_G5	G5	ST7701S RGB
10	I2C0_SDA	SDA	I2C bus
11	I2C0_SCL	SCL	I2C bus
12	LCD_G2	G2	ST7701S RGB
13	LCD_G1	G1	ST7701S RGB
14	PIR	AM312	PIR sensor
15	LCD_SPI_SDA	LCD_SDA	ST7701S SPI
16	LCD_SPI_CS	LCD_CS	ST7701S SPI
17	IOEXP_RESET	RST	PCAL9538A reset
18	IOEXP_A1	A1	PCAL9538A address
21	LCD_B5	B5	ST7701S RGB
38	LCD_HSYNC	LCD_HSYNC	ST7701S sync
39	LCD_VSYNC	LCD_VSYNC	ST7701S sync
40	LCD_DE	LCD_DE	ST7701S enable
41	I2S_MIC_DOUT	DOUT	Microphone
42	I2S_MIC_BCLK	BSCK	Microphone
45	LCD_B2	B2	ST7701S RGB
46	LCD_R1	R1	ST7701S RGB
47	LCD_B4	B4	ST7701S RGB
48	LCD_B3	B3	ST7701S RGB

PCAL9538A IO Expander (I2C 0x70)

Pin	Net	Function	Direction
P0	G4	LCD RGB data (static)	Output
P1	G3	LCD RGB data (static)	Output
P2	R5	LCD RGB data (static)	Output
P3	R4	LCD RGB data (static)	Output
P4	R3	LCD RGB data (static)	Output
P5	PROG_EN	Reed switch (magnet)	Input
P6	NC	Not connected	—
P7	NC	Not connected	—

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Known Hardware Issues (Errata)

ERRATA 1: RX0-VSYS Wire (ROOT CAUSE — CORRECTED)

Original diagnosis: LCD ESD diode clamping GPIO0. Actual root cause: Physical wire between ESP32-S3 RX0 (GPIO44) and VSYS (BQ25895 SW output).

• Net name in schematic: RX0_EN_REG3.3
• Components on this net (4 pins):
  • U3 pin 36 (RXD0) — ESP32-S3 UART0 RX
  • FlashPort pin 4 — Debug header UART RX
  • D6 pin 2 — BAT760-7 Schottky diode
  • R32 pin 2 — 10kΩ resistor to GND
• Effect: Switching noise from BQ25895 buck converter couples into ESP32-S3 power domain, causing spurious resets into download mode
• Fix: Remove the physical wire. Firmware mitigations (PWR_EN hold, GPIO0 pull-up) retained as belt-and-suspenders.

ERRATA 2: GPIO0 Boot Strap Trap

Net: IO0_LCD_RST Components on this net (4 pins):

• U3 pin 27 (IO0) — ESP32-S3 boot strap pin

• R23 pin 2 — 10kΩ pull-up to +3.3V

• CN1 pin 35 — LCD FPC connector (ST7701S reset)

• FlashPort pin 5 — Debug header GPIO0

• GPIO0 is shared between ESP32-S3 boot strap and ST7701S LCD reset

• R23 (10kΩ) pulls GPIO0 high for normal boot

• When LCD is unpowered, ESD diode can clamp GPIO0 low (secondary issue)

• Mitigation: PWR_EN asserted before ROM samples GPIO0; GPIO0 held high via RTC during sleep

• Status: RETAINED as belt-and-suspenders; not the primary root cause

ERRATA 3: BQ25895 Watchdog

• BQ25895 internal watchdog can fire, resetting charger registers to defaults
• Firmware detects via REG_0C bit 7 and re-applies settings
• Mitigation: Watchdog disabled in charger init

ERRATA 4: Weak VBUS Boot Throttle

• At boot, if VBUS is weak (<4300mV or SDP/UNKNOWN/NONE), charger throttled to 300mA
• Re-enabled when VBUS recovers (≥4400mV, stable)
• Status: Good practice for USB-powered scenarios

ERRATA 5: LCD Noise (v2.8 specific)

• 5 RGB data bits held static by IO expander causes visible dithering artifacts
• Mitigation: NRCTRL noise reduction + SECTRL sharpness control enabled
• VOP override: VRHS raised from 0x6D to 0x70 for better contrast

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Critical Net Names

Net	Connections	Notes
RX0_EN_REG3.3	GPIO44 ↔ VSYS path	THE problematic wire
PWR_EN	GPIO1 → MIC94073 EN	Power enable for SW_3.3V
IO0_LCD_RST	GPIO0 ↔ ST7701S RST	Boot strap + LCD reset
VSYS	BQ25895 SYS → system	Main switched rail
VBUS	USB-C → BQ25895 IN	USB 5V input
SW_3.3V	MIC94073 OUT → LCD, IO expander	Switched peripheral rail
PROG_EN	PCAL9538A P5 ↔ RS1	Reed switch input
BAT	BQ25895 BAT ↔ CON_BAT	Battery connection
PMID	BQ25895 PMID decoupling	Input decoupling
REGN	BQ25895 REGN decoupling	Charge pump LDO
SW	BQ25895 SW ↔ L3	Switching node
SDA	GPIO10 ↔ U11/U12	I2C data
SCL	GPIO11 ↔ U11/U12	I2C clock
A0	GPIO8 → PCAL9538A	I2C address bit 0
A1	GPIO18 → PCAL9538A	I2C address bit 1
RST	GPIO17 → PCAL9538A	IO expander reset
EN	PCAL9538A enable	—
USB_DP	USB-C D+	USB data
USB_DN	USB-C D-	USB data
BL_PWM	GPIO6 → ST7701S	Backlight control
TX0_AP_BTN	—	Button/UART