Hardware Design Reference
Version: 20240613
Introduction
This document describes the hardware design for keep-alive Wi-Fi locks. The keep-alive Wi-Fi solution enables persistent connections with ultra-low power consumption, minimizing power usage to microamperes (µA) during sleep mode. The solution integrates a highly-integrated radio frequency (RF) processor chip, an external microcontroller unit (MCU), and peripheral components. It supports both printed circuit board (PCB) antennas and IPEX antennas, facilitating comprehensive wireless connections across multiple protocols. Serial communication is also supported for data transmission with MCUs in other services.
1 Hardware Design
The keep-alive Wi-Fi no-code development solution is based on the HPWSMS1 module provided by Tuya. Refer to the HPWSMS1 Module Datasheet for more information. This module supports two types of antennas:
- PCB antenna: Detailed design information is available in the Structural Design section under inverted-F antenna diagrams.
- IPEX antenna: This type of antenna can be designed based on specific product structures.
1.1 Schematic Diagrams
- Power Supply Design: The circuit operates at a 3.3V working voltage. The Wi-Fi chip is powered separately from the RTL8762. Magnetic beads FB1 and FB2 are included as current test points. Figure 1: A schematic shows a 3.3V power input connected to filter capacitors (C1: 10uF/16V, C2: 1uF/6.3V, C3: 0.1uF/6.3V) and then to the Wi-Fi chip (RTL8762). Magnetic beads FB1 (100MHz/1500mA) and FB2 (100MHz/1000mA) are included for current testing, connected to VBAT_8762 and VDDIO_8762 respectively.
- Antenna Design Rules for HPWSMS1:
- The 3.3V_Wi-Fi power pin connects to a filter capacitor.
- Pins 49, 29, 82, and 94 each connect to a separate 1 µF/10V filter capacitor.
- Pin 98 connects to a 10 µF/10V filter capacitor.
- Pin 78 connects to a 0.1 µF/16V filter capacitor.
- Module Supported Pins: The module supports pins including HOST_BYP_ULP_WAKEUP, SLEEP_IND_FROM_DEV, ULP_GPIO_6, ULP_GPIO_5, and RESET_N. Each of these pins connects in series with a resistor to a specific pin on the RTL8762 to enable its function. Figure 2: A communication diagram illustrating connections between the Wi-Fi module and RTL8762. Key connections include WIFI_UART1_RX and WIFI_UART1_TX for communication. Other pins shown are related to wake-up, GPIO, and reset functions, each connected via a resistor to the RTL8762. Test points are indicated for flashing tools.
- RESET_N Signal Processing: A 10 mΩ pull-down resistor is used for the RESET_N signal. Figure 3: A schematic shows a pull-down resistor configuration for the RESET_N signal, featuring resistors R3 (1K/1%) and R4 (10M), and capacitor C9 (1nF/25V).
- POC_OUT and POC_IN Pins: Pin 92 (POC_OUT) and pin 65 (POC_IN) are connected through a 0R resistor. POC_IN is reserved for connection to resistor R10 to process control signals of RTL8762. Figure 4: A schematic illustrates the connection of pins POC_OUT and POC_IN via an OR gate and resistor R10, used for processing control signals of the RTL8762.
- RF Channel and Impedance Matching: The RF channel connects only to pin 32. The layout design requires 50 Ω impedance matching. Either a PCB antenna or an IPEX antenna can be used. Figure 5: A schematic shows the RF channel connected to pin 32 of the RTL8762. It depicts impedance matching components (resistors R1, R16, R17, capacitor C8, inductor L1) and connections to antennas (ANT1, ANT2) and the Wi-Fi chip.
- RTL8762 Development Board Design Rules:
- Crystal Oscillator: Recommended specifications are 40 MHz ±10 ppm, 9 pF, -30°C to +85°C, SX3225 (SMT). Frequency deviation should be at most 10 ppm. For lower power applications, 32.768 kHz ±20 ppm, 7 pF, SMD2012 is recommended.
- VDD12 Capacitor: A capacitor of at least 0.1 µF X5R 6.3V should be connected to the VDD12 power pin.
- L2 Inductor: Specifications include rated current > 0.5A, DC resistance (DCR) < 1 Ω, and self-resonant frequency (SRF) > 40 MHz.
- C15 Capacitor: Recommended specifications are 2.2 µF, X5R, and 10V.
- Voltage: VBAT_8762 and VDDIO_8762 should reach 3.3V.
- Filter Capacitors: Pins 39 and 21 use a combination of 1 µF/6.3V and 0.1 µF/6.3V filter capacitors. Pin 32 uses a 4.7 µF/6.3V filter capacitor.
- RESET Signal: The RESET signal is pulled up to VBAT_8762 with a 10 kΩ resistor.
- Test Points: Test points must be reserved for debugging and production testing, including:
- P0_3: For viewing logs.
- UART2_TX/UART2_RX: For firmware flashing and updates.
- SWDCLK/SWDIO: For Joint Test Action Group (JTAG) debugging.
- 3V3 and GND: For debugging.
Figure 6: Diagrams show pinouts of the RTL8762 chip and associated connections, highlighting reserved test points for signals like P0_3, UART2_TX/RX, SWDCLK/SWDIO, and 3V3/GND.
1.2 PCB Design Reference
- The 3.3V_WIFI power supply for the HPWSMS1 is designed in a star network topology. The trace width must be at least 20 mil. Figure 7: A PCB layout illustration depicts a star network configuration for the 3.3V_WIFI power supply, emphasizing trace routing.
- The L2 inductor of RTL8762 is placed close to the chip pin to minimize the inductive loop. Figure 8: A PCB layout illustration shows the placement of the L2 power inductor close to the RTL8762 chip to minimize inductive loops.
- Ground vias are added around the RF channel to provide 50 Ω impedance matching. Figure 9: A PCB layout illustration demonstrates the use of ground vias around the RF channel to ensure 50 Ohm impedance matching.
- Test points are easily accessible by a test jig. Output signals include 3.3V, GND, P0_3, WIFI_UART1_TX, WIFI_UART1_RX, UART2_TX, UART2_RX, SWDCLK, and SWDIO.
2 Structural Design
When designing a product, determine the antenna location first. You can choose between a PCB antenna or an IPEX antenna.
Note: It is recommended to confirm the antenna location and related considerations with the antenna manufacturer at the beginning of the structural design.
2.1 Usage of PCB Antennas
- For PCB antennas, it is recommended to place the module antenna at least 15 mm away from other metal components to optimize Wi-Fi performance. Traces and copper pour areas are prohibited within the antenna area of the PCB to prevent performance degradation.
- The final performance of a PCB antenna is influenced by multiple factors including product structure, materials, module location, and the dimensions and shape of the backplane. Actual testing is required to determine the overall product performance.
- PCB antennas can be used in specific structural configurations, such as attachment to the non-metal shell of the device or when sufficient clearance is reserved. The following figures illustrate recommended PCB layouts. Ensure no substrate medium is directly below the antenna, and avoid copper pour areas around it to minimize interference. Figure 10: A diagram shows a recommended PCB layout for a PCB antenna placed outside the backplane frame, with a 6mm clearance.Figure 11: A diagram illustrates a PCB layout where the antenna is positioned along the backplane frame, with 5mm clearance on the sides and 6mm clearance on the top/bottom, indicating no copper pour in specified red boxes.Figure 12: A diagram shows a PCB layout with the antenna along the midline of the backplane, featuring hollowed-out frames around the antenna and 5mm clearance areas.
- Based on these layouts, ensure no substrate medium or metal parts are directly below or above the PCB antenna, and keep it away from copper sheets to maximize radiation effect.
2.2 Usage of IPEX Antennas
- An IPEX antenna is a suitable choice for Wi-Fi modules used in devices. Position the antenna optimally, away from interference from metal parts.
- Flexible printed circuit (FPC) antennas can be attached to a non-metal shell or secured using an antenna bracket.
- The placement of an IPEX antenna depends on the overall device design and structure. Evaluate the antenna location and debug RF performance based on the actual structural design to comply with certifications and regulations. While the module can determine backplane RF performance, it cannot cover the overall performance of different forms.
- The following figure shows recommended specifications for the IPEX connector. Figure 13: Mechanical drawings and PCB layout dimensions for an IPEX connector, detailing diameter, length, and mounting hole specifications.
Other Layout Rules:
- Maintain a distance of 3 cm or more between the module and components like speakers, power switches, cameras, HDMI connectors, USB connectors, and other high-speed signals to prevent interference.
- Reserve adequate clearance area below the antenna. No wiring or other medium layers should be present in this area to avoid interference from structural parts.
- Avoid metal shielding near the antenna. If co-channel interference occurs, evaluate its impact and ensure isolation.
- Antenna radiation directions must not be blocked by metal.
3 Bill of Materials
| Item code | Item description | Manufacturer-managed Manufacturer model | Quantity | Position |
|---|---|---|---|---|
| 1.14.99.00020 | Other connectors, IPEX antenna mount, UB06000004A, 2 mm outer ring and 0.5 mm inner pin, gold-plated phosphor bronze, -40°C–+90°C, and SMT | Ubuant UB06000004A | 1 | ANT1 |
| 2.06.03.01057 | Material combination, ceramic capacitor, SMT, X5R, 10 µF, ±10%, 16V, and 0805 | Capacitor 201 | 1 | C1 |
| 2.06.03.01148 | Material combination, ceramic capacitor, SMT, X5R, 1 µF, ±20%, 6.3V, and 0201 | Capacitor 292 | 8 | C2, C10, C16, C17, C19, C22, C24, and C32 |
| 2.06.03.00857 | Material combination, ceramic capacitor, SMT, X5R, 0.1 µF, ±10%, 6.3V, and 0201 | Capacitor 001 | 7 | C3, C11, C18, C20, C21, C23, and C25 |
| 2.06.03.01150 | Material combination, ceramic capacitor, SMT, X5R, 10 µF, ±20%, 10V, and 0402 | Capacitor 294 | 1 | C4 |
| 2.06.03.01154 | Material combination, ceramic capacitor, SMT, X5R, 1 µF;±10%, 10V, and 0402 | Capacitor 298 | 3 | C5, C6, and C29 |
| 2.06.03.01031 | Material combination, ceramic capacitor, SMT, C0G, 22 pF, ±5%, 50V, and 0402 | Capacitor 175 | 1 | C8 |
| 2.06.03.01145 | Material combination, ceramic capacitor, SMT, X5R, 4.7 µF, ±20%, 6.3V, and 0402 | Capacitor 289 | 1 | C12 |
| 2.06.03.00972 | Material combination, ceramic capacitor, SMT, X5R, 2.2 µF, ±10%, 10V, and 0402 | Capacitor 116 | 1 | C15 |
| 2.06.03.01136 | Material combination, ceramic capacitor, SMT, C0G, 12 pF, ±5%, 50V, and 0201 | Capacitor 280 | 2 | C26 and C27 |
| 1.04.03.00007 | Magnetic bead, 180R@100 MHz, 0.09R, 1.5A, 0603, and SMT | Sunlord PZ1608D181-1R5TF | 1 | FB1 |
| 1.04.03.00009 | Magnetic bead, 120R@100 MHz, 0.12R, 1A, 0402, and SMT | Sunlord PZ1005U121-1R0T | 1 | FB2 |
| 1.04.02.00625 | Power inductor, 4.7 µH, 0.2, 0.125R, 1.09A, 3.0 × 3.0 × 1.5 mm, and SMT** | Sunlord SWPA3015S4R17MT | 1 | L2 |
| 2.06.03.00028 | Material combination, SMD resistor, 0402, 0R, ±5%, and 1/16W | SMD resistor 4355 | 13 | R1 R2 R5 R7 R8 R9 R11 R12 R13 R14 R16 L1 |
| 2.06.03.00032 | Material combination, generic resistor, 1K, ±1%, 0402, 1/16W, and SMT | Generic resistor 4361 | 1 | R3 |
| 2.06.03.00733 | Material combination, generic resistor, 10M, ±5%, 0201, 1/20W, and SMT | Resistor 688 | 1 | R4 |
| 2.06.03.00047 | Material combination, generic resistor, 10K, ±5%, 0402, 1/16W, SMT, and 50V | Resistor 002 | 1 | R15 |
| 1.17.13.00587 | RF transceiver IC, Bluetooth, -40°C–+105°C, QFN40, and SMT | Realtek RTL8762CMF | 1 | U2 |
| 2.01.01.10273 | General Wi-Fi module, Wi-Fi and Bluetooth Low Energy, HPWSMS1, RS9116, and external antenna (welded to the backplane without an IPEX mount, the antenna mount placed on the backplane) | Tuya HPWSMS1 | 1 | U1 |
| 2.06.03.00859 | Material combination, ceramic capacitor, SMT, X7R, 0.1 µF, ±10%, 16V, and 0402 | Capacitor 003 | 1 | C7 and C28 |
| 2.06.03.00981 | Material combination, ceramic capacitor, SMT, X5R, 1 nF, ±10%, 25V, and 0201 | Capacitor 125 | 1 | C9 |
| 1.03.02.00724 | Crystal oscillator, 32.768 kHz, ±20 ppm, 7 pF, 65K, -40°C–+85°C, 2012, and SMT | EPSON X1A00006100106xx | 1 | Y1 |
| 1.03.02.00762 | Crystal oscillator, 40 MHz, ±10 ppm, 15 pF, 30R, -40°C–+85°C, ±20 ppm, 3225, and SMT | Faith Long 3S40000066 | 1 | Y2 |
| 1.21.05.00764 | PCB substrate, S-MSL1-SHX-001_V1.0.0, 36 × 36 × 1.2 mm, 4L, electroless nickel immersion gold (ENIG), green and white, plated half holes, and halogenated** | 1 | ||
| 1.02.99.00026 | Ceramic capacitor, SMT, X5R, 1 nF, ±10%, 25V, and 0201 | Murata GRM033R71E1102KA01D | 1 | C9 |
| 1.02.05.00842 | Ceramic capacitor, SMT, X7R, 1 nF, ±10%, 25V, and 0201 | Walsin 0201B102K25/0CT | / | / |
| 1.02.05.00837 | Ceramic capacitor, SMT, X7R, 1 nF, ±10%, 25V, and 0201 | Yageo CC0201KRX7R/8BB102 | / | / |
| 1.03.02.00724 | Crystal oscillator, 32.768 kHz, ±20 ppm, 7 pF, 65K, -40°C–+85°C, 2012, and SMT | EPSON X1A00006100/06xx | / | / |
4 Solution Process
The following describes the keep-alive Wi-Fi no-code development process:
- ID Design: Customer completes the initial ID design.
- Structural Design: Customer completes the structural design. The Antenna Manufacturer confirms antenna location and evaluates the program.
- Hardware Development: Customer completes the schematic diagram and PCB design. Tuya provides support by reviewing the schematic diagram and PCB design. The Antenna Manufacturer uses a prototype to confirm antenna effect.
- Trial Production Test: Customer confirms the production test process and passes the production test.
- Whole Device Test: Customer completes the whole device performance test. Tuya supports keep-alive performance testing.
