1. System Overview

▫️ Design Goals

• Implement automatic switching between dual power inputs (Type-C/Battery), 5V (Type-C)/4.2V (Battery).
• Implement power on/off through long press of button using EC190708.
• Integrate Ai-M61-32S Wi-Fi 6/BLE module for wireless communication.
• Implement offline voice wake-up and interruption through VB6824 offline voice chip, supporting audio capture, playback, and ACE echo cancellation.

▫️ Overall Architecture Diagram

2. Module Design Specifications

▫️ Power Module

🔹 Function Description

• Dual power input: Automatic switching between Type-C (5V) and lithium battery (3.7V), with priority given to Type-C power supply;
• Charging management: TP4054 implements constant current/constant voltage charging for lithium battery, with maximum charging current of 500mA;
• Boost output: When powered by battery, outputs 5V system voltage through boost chip (such as STI3508C);
• Buck output: Steps down 5V to 3.3V to power modules and voice chips.

🔹 Design Points

• TP4054 key parameters:
  • Charging current setting: $I_{BAT}=1000/R_{PROG}$ (e.g., R=5kΩ → 200mA), can also refer to the table below for configuration.

$R_{PROG}$(KΩ)	$I_{CHG}$(mA)
5.1	200
4.7	250
4.3	300
4.0	400
3.7	500
3.4	600
3.1	667
2.8	800
2.5	1000
2.2	1200

• BAT pin requires a ceramic capacitor of 10μF or more;
• Boost circuit design:
  • Boost IC model used: STI3508C;
  • Feedback resistor calculation: $V_{OUT}=V_{REF}\ast (1+R_1/R_2)$, where $V_{REF}$=0.6V. (e.g., R1=110kΩ, R2=15kΩ → 5.00V);
  • Inductor selection: 2.2μH recommended.

(Click to view) Reference circuit:

• Recommended selection table for common voltages:

$V_{OUT}$ (V)	R1 (KΩ)	R2(KΩ)	C2 (uF)	L(uH)
5	110	15	22	2.2~6.8
9	130	9.31	22	4.7~10
10	24	200	5.11	22

• Buck circuit:

⁉️Why are both boost and buck circuits needed?

A: The purpose of the boost is to ensure a stable power supply for the power amplifier chip when powered by the battery, maintaining consistent audio quality. The buck circuit is mainly used to power the WiFi module and audio chips.

• DC/DC chip signal: RT8059;
• Feedback resistor calculation: $V_{OUT}=V_{REF}\ast (1+R1/R2)$, where $V_{REF}$=0.6V, for example (R1=68KΩ, R2=15KΩ → 3.32V);

(Click to view) Reference circuit:

• Power switching logic:
  • When Type-C is inserted, cut off the battery power supply path through MOSFET (such as AO3401).

🔹 Interface Definition

Pin/Net Name	Type	Description
USB_5V	Input	Type-C 5V Power Input
BAT+	Input/Output	Lithium battery positive terminal (3.7V)
VCC_5V	Output	System main power supply (5V±5%)
VCC_3V3	Output	Power supply for modules and voice chips (3.3V ±5%)

🔹 Layout Recommendations

• Thermal management: TP4054 and boost chip should be kept away from sensitive analog circuits, with adequate copper coverage on ground heat dissipation pads;
• Decoupling capacitors: Parallel 10μF electrolytic capacitor + 0.1μF ceramic capacitor at VCC_5V and VCC_3V3 output terminals.

▫️ AiM6132S Module

🔹 Function Description

• Provides Wi-Fi/BLE dual-mode wireless connection, communicates with main controller through UART;
• Operating voltage: 3.3V@500mA peak.

🔹 Design Points

• Power design:
  • Recommended DC/DC chip: RT8059, input needs to be ≥4V, output 3.3V;
  • Decoupling capacitors: 10μF+0.1μF close to the module VCC pin.
• UART interface:
  • LOG:
    • Interface: RX0 (RX) & TX0 (TX);
    • Default baud rate: 2000000.
  • Offline voice communication port:
    • Interface: IO19 (RX) & IO18 (TX);
    • Default baud rate: 2000000.
• Antenna layout:
  • Copper covering is prohibited in the PCB antenna area, with a clearance area of ≥5mm around.
• Module interface definition:

Pin Number	Pin Name	Description
1	GND	Power ground
2	VDD33	3v3 power supply
3	CHIP_EN	Module reset pin
4	GPIO0	Reserved I2C pin: I2C_SCL
5	GPIO1	Reserved I2C pin: I2C_SDA
6	GPIO16	SPI screen RS pin
7	GPIO17	DCX_SPI_SCL
8	GPIO12	CSX_SPI_CS
9	GPIO14	NC
10	GPIO15	SPI_MOSI
11	GPIO18	UART TX signal of offline voice chip
12	GPIO19	UART RX signal of offline voice chip
13	GPIO10	Led out GPIO10
14	GPIO13	Led out GPIO13
15	GPIO11	NC
16	GPIO3	DVP_RSTB
17	GPIO20	AI_LCD
18	GPIO4	External Flash, not available
19	GPIO5	External Flash, not available
20	GPIO6	External Flash, not available
21	GPIO7	External Flash, not available
22	GPIO8	External Flash, not available
23	GPIO9	External Flash, not available
24	USB_DP	USB_DP
25	USB_DM	USB_DM
26	GPIO23	DVP_MCLK
27	GPIO2	Boot control pin, high level at power-on enters programming mode
28	GPIO24	DVP_D0
29	GPIO28	DVP_HYSNC
30	GPIO26	DVP_D2
31	GPIO25	DVP_D1
32	GPIO27	DVP_D3
33	GPIO29	DVP_VSYNC
34	GPIO30	DVP_CLK
35	GPIO31	DVP_D4
36	TX0	UART_TX
37	RX0	UART_RX
38	GPIO32	DVP_D5
39	GPIO33	DVP_D6
40	GPIO34	DVP_D7

▫️ SPI Color Screen Driver Circuit

• The selected screen supports 5V power supply, uses IO2 to control the backlight, and realizes software control of brightness
• Pin header design, the screen is connected to the baseboard in the form of pin headers

▫️ Offline Voice Module (VB6824+8002A)

🔹 Function Description

• VB6824 implements voice wake-up word recognition and audio encoding/decoding, interacts with Ai-M61-32S through UART;
• 8002A power amplifier drives 8Ω/2W speaker, supports PWM input.

🔹 Design Points

• Audio circuit:
  • A 100nF DC blocking capacitor is connected in series between VB6824 and 8002A;
  • Speaker traces need to be thickened (≥0.5mm) to avoid being parallel to digital signal lines.
• Microphone design:
  • It is recommended to use an omnidirectional cylindrical omnidirectional microphone with a sensitivity of -29dB ±3dB;
  • Microphone power supply requires RC filtering (4.7KΩ+10uF).
• AEC echo cancellation:
  • The speaker output pin (DACR) is connected in series with a 0.1uF capacitor and a 5.1KΩ resistor to PA1 and PA0;

(Click to view) Reference circuit:

• Power amplifier configuration:
  • 8002A gain setting: Avd= 2×(Rf/Ri) (default Rf=30K, Ri=10K, gain 6 times).
• VB6824 main interface definition:

Pin Number	Pin Name	Description
1	USBDM	Programming and LOG pin
2	USBDP	Programming and LOG pin
3	PA1	AEC echo cancellation acquisition pin
4	PA0	AEC echo cancellation acquisition pin
5	PC7/MIC_BIAS	Microphone driver pin
6	MIC	MIC input interface
11	DACR	Audio signal output pin, output to audio power amplifier chip
14	PB10	RX signal of communication UART
15	PB9	TX signal of communication UART
17	PB5	Power amplifier control signal

3. Debugging and Testing

▫️ Power Test Items

Test Point	Expected Value	Allowable Error
TP4054 PROG	0.5V (500mA)	±5%
VCC_5V	5.0V	±3%
DC/DC Output	3.3V	±2%

▫️ Voice Module Verification

• Wake-up test: At a distance of 30cm, when the signal-to-noise ratio is ≥15dB, the wake-up rate is ＞95%;
• Audio distortion: THD of 1kHz sine wave output ＜1%.