270 lines
12 KiB
Markdown
270 lines
12 KiB
Markdown
# ESP32‑S3 Wearable Sensor Board – Hardware Design Specification
|
||
|
||
**Document Version:** 1.0
|
||
**Target Audience:** PCB designer / hardware engineer
|
||
**Status:** Ready for implementation
|
||
|
||
***
|
||
|
||
## Document index
|
||
|
||
- [1. Overview](#1-overview)
|
||
- [2. MCU and wireless](#2-mcu-and-wireless)
|
||
- [3. Power – battery, charging, and gauge](#3-power––battery-charging-and-gauge)
|
||
- [4. USB‑C interface and firmware protection](#4-usb-c-interface-and-firmware-protection)
|
||
- [5. Power‑supply architecture](#5-power-supply-architecture)
|
||
- [6. Motion sensing (IMU)](#6-motion-sensing-imu)
|
||
- [7. Real‑time clock (RTC)](#7-real-time-clock-rtc)
|
||
- [8. Deep‑sleep and power‑gating](#8-deep-sleep-and-power-gating)
|
||
- [9. Display and I²C peripherals](#9-display-and-i2c-peripherals)
|
||
- [10. GPIO exposure and modularity](#10-gpio-exposure-and-modularity)
|
||
- [11. Power‑pin distribution per GPIO](#11-power-pin-distribution-per-gpio)
|
||
- [12. Size, PCB layers, and mechanical constraints](#12-size-pcb-layers-and-mechanical-constraints)
|
||
- [13. External power input and protection](#13-external-power-input-and-protection)
|
||
- [14. Bill of Materials (BOM) draft](#14-bill-of-materials-bom-draft)
|
||
|
||
***
|
||
|
||
## 1. Overview
|
||
|
||
This document defines the hardware design requirements for a **compact wearable sensor board** based on the **ESP32‑S3** (preferred) or **ESP32‑C3**. The board targets sports/impact‑sensing applications (fist/leg strikes) and must balance:
|
||
|
||
- Tiny size for wearable use.
|
||
- Long‑term battery life via deep‑sleep and power‑gating.
|
||
- High‑integrity IMU and power‑monitoring (gas‑gauge, RTC).
|
||
|
||
The designer must translate this into a **schematic and double‑sided PCB layout** that meets all constraints listed below.
|
||
|
||
***
|
||
|
||
## 2. MCU and wireless
|
||
|
||
- **MCU:**
|
||
- Primary: **ESP32‑S3** (small‑form‑factor, integrated Wi‑Fi/BLE, USB‑UART, 45+ GPIOs).
|
||
- Alternative (only if size is critical and Wi‑Fi/BLE robustness is secondary): **ESP32‑C3**.
|
||
- **Connectivity:**
|
||
- 2.4 GHz **Wi‑Fi 802.11 b/g/n**.
|
||
- **Bluetooth 5.0 (BLE)**.
|
||
- **RF layout:**
|
||
- Use either an **on‑board PCB antenna** or a small external antenna connector, following Espressif’s ESP32‑S3 hardware design guidelines.
|
||
- Provide proper RF‑matching network and keep‑out zones around the antenna.
|
||
|
||
***
|
||
|
||
## 3. Power – battery, charging, and gauge
|
||
|
||
- **Battery:**
|
||
- Single‑cell **Li‑Po / Li‑Ion** (nominal 3.7 V).
|
||
- **Charging:**
|
||
- Include a **Li‑Po charge IC** (e.g., TP4056, BQ2409x‑style, or similar modern IC) that:
|
||
- Accepts **5 V from USB‑C** → charges the battery.
|
||
- Reports charge status via **GPIO‑visible signals** (e.g., CHRG, DONE).
|
||
- Charging current: **100–500 mA** typical (designer’s choice based on thermal and USB limits).
|
||
- **Battery gauge (SoC monitoring):**
|
||
- Use a **gas‑gauge IC** (e.g., **MAX170xx family**, or similar) to measure:
|
||
- Battery voltage.
|
||
- Current.
|
||
- State‑of‑Charge (%).
|
||
- Interface: **I²C** (shared bus with IMU and RTC).
|
||
- This is **mandatory**; do not rely purely on ADC‑based voltage‑only estimation.
|
||
|
||
***
|
||
|
||
## 4. USB‑C interface and firmware protection
|
||
|
||
- **USB‑C role:**
|
||
- One **USB‑Type C receptacle** serving:
|
||
- **Battery charging** (via Li‑Po charge IC).
|
||
- **ESP32‑S3 programming and serial communication** (via built‑in USB‑UART/JTAG).
|
||
- **D‑ / D+ SMD jumpers:**
|
||
- Bring **D‑** and **D+** from the USB‑C connector to **SMD jumper pads** (e.g., 0603/0402‑style pads).
|
||
- When the pads are **shorted by solder**, D‑/D+ are connected to the ESP32‑S3.
|
||
- When the shorts are **desoldered**, D‑/D+ are disconnected, preventing:
|
||
- User‑induced firmware re‑flash.
|
||
- Accidental corruption of the device in the field.
|
||
- **USB protection:**
|
||
- Include **ESD protection / 5‑V clamp** on USB lines.
|
||
- Limit current via USB‑compliant resistor or IC‑based current‑limiting.
|
||
|
||
***
|
||
|
||
## 5. Power‑supply architecture
|
||
|
||
- **3.3 V main rail:**
|
||
- Provide a **3.3 V regulator** for the ESP32‑S3, IMU, OLED, and 3.3 V peripherals.
|
||
- Prefer a **buck (step‑down) converter** over an LDO for efficiency and higher current capability.
|
||
- Target: **3.3 V @ 300–500 mA** continuous (or higher if justified by load).
|
||
- **Boost converter / 5 V booster:**
|
||
- A **boost converter** (e.g., 1.8–4.2 V input → 5 V output) must power:
|
||
- LED strips.
|
||
- Other **5 V peripherals**.
|
||
- The **enable pin** of the booster must be driven by a **GPIO** of the ESP32‑S3.
|
||
- When the MCU goes into **deep‑sleep**, this GPIO must be **set to low** to disable the booster.
|
||
- **Isolation:**
|
||
- Ensure the **5 V rail** is isolated from 3.3 V logic (Schottky diodes or MOSFET isolation if needed).
|
||
|
||
***
|
||
|
||
## 6. Motion sensing (IMU)
|
||
|
||
- **General requirement:**
|
||
- Use a **6‑axis or 9‑axis IMU** for impact / strike detection, supporting:
|
||
- High‑g capability (≥ 80 g) for punches/kicks.
|
||
- Low‑noise gyro for angular motion.
|
||
- Do **not** use obsolete parts like MPU‑9250 or MPU‑6050 due to supply and counterfeit risks.
|
||
- **Preferred IMU:**
|
||
- **ST LSM6DSV80X** (or equivalent) is recommended because:
|
||
- 6‑axis IMU in a **2.5×3 mm** package.
|
||
- Dual accelerometer paths: **16 g low‑g** and **80 g high‑g**.
|
||
- Gyroscope and embedded AI‑style FSM/MLC for impact detection and motion states.
|
||
- Supports **I²C and SPI**.
|
||
- **Interface and power:**
|
||
- Run the IMU from the **3.3 V rail**.
|
||
- Connect to ESP32‑S3 via **I²C** (shared with battery gauge and RTC).
|
||
- Expose all configurable pins (interrupts, reset, etc.) on **solder pads** so they can be jumpered or disconnected.
|
||
|
||
***
|
||
|
||
## 7. Real‑time clock (RTC)
|
||
|
||
- **Function:**
|
||
- Provide **accurate timekeeping** during long‑term battery‑powered operation and deep‑sleep.
|
||
- **Requirements:**
|
||
- I²C‑compatible RTC module (e.g., common 32‑kHz RTC chips).
|
||
- **Tiny coin‑cell footpring** for a **3‑V rechargeable** cell or supercap‑backup (e.g., CR1220‑style).
|
||
- Alarm / interrupt output to a **GPIO** to wake the MCU from deep‑sleep.
|
||
- **Power:**
|
||
- Main power from **3.3 V rail**.
|
||
- Backup power from coin cell / supercap.
|
||
|
||
***
|
||
|
||
## 8. Deep‑sleep and power‑gating
|
||
|
||
- **System behavior in deep‑sleep:**
|
||
- In deep‑sleep, the ESP32‑S3 must **disable all non‑critical external peripherals** and **isolate power rails** to minimize current draw.
|
||
- Targets for shut‑down:
|
||
- **5 V booster** (GPIO‑driven enable → low).
|
||
- Any external modules powered by external 5 V or switchable rails.
|
||
- **Power‑gating strategy:**
|
||
- Use **MOSFET‑based power‑gating** or **enable‑controlled DC/DC converters** for:
|
||
- 5 V booster output.
|
||
- External I²C peripherals not needed during sleep.
|
||
- The MCU must control **enable signals** for these regulators/MOSFETs via GPIOs.
|
||
|
||
***
|
||
|
||
## 9. Display and I²C peripherals
|
||
|
||
- **OLED display:**
|
||
- Provide a **standard footprint / connector** for an **I²C OLED display** (e.g., 0.96" 128×64).
|
||
- Pins at connector:
|
||
- `VCC` (3.3 V).
|
||
- `GND`.
|
||
- `SDA` (I²C data).
|
||
- `SCL` (I²C clock).
|
||
- Power from the **3.3 V rail**.
|
||
- **General I²C:**
|
||
- Provide **exposed solder pads** for a **secondary I²C bus** or breakout of the main I²C bus for:
|
||
- Extra sensors.
|
||
- Expansion modules.
|
||
- Use appropriate **pull‑up resistors** (e.g., 4.7 kΩ) sized for selected bus speed.
|
||
|
||
***
|
||
|
||
## 10. GPIO exposure and modularity
|
||
|
||
- **All GPIOs:**
|
||
- Every **ESP32‑S3 GPIO** must be accessible:
|
||
- As **through‑hole pads**, **0.1" header pins**, or **edge‑mountable pads**.
|
||
- Labeled with: **GPIO number + function** (e.g., `GPIO21 – I2C_SDA`).
|
||
- **External‑control signals:**
|
||
- Any GPIO that controls:
|
||
- Booster enable.
|
||
- Other external modules / regulators.
|
||
- Must be connected via **SMD jumper pads** (two pads with a short‑able bridge).
|
||
- When the bridge is **soldered**, the MCU controls that function.
|
||
- When the bridge is **desoldered**, that function is disconnected, allowing modular removal of that side of the board.
|
||
|
||
***
|
||
|
||
## 11. Power‑pin distribution per GPIO
|
||
|
||
To ensure easy connection to external peripherals without extra wiring:
|
||
|
||
- For **every GPIO pad / connector**, place neighboring pads for:
|
||
- `GND`.
|
||
- `3V3`.
|
||
- `5V`.
|
||
- **Preferred layout patterns:**
|
||
- Pin‑header style: `[GPIO_X][GND][3V3][5V]` repeated.
|
||
- Solder‑pad array:
|
||
- One row for `GND`.
|
||
- One row for `3V3`.
|
||
- One row for `5V`.
|
||
- One row for `GPIO_X` signals.
|
||
- **Electrical rules:**
|
||
- Connect all `GND` pads to the **main ground plane**.
|
||
- Connect `3V3` pads to the **main 3.3 V buck output**.
|
||
- Connect `5V` pads to the **boost‑converter output**, enabled only when the booster is active.
|
||
- Size power traces and vias to handle **high‑current loads** (e.g., LED strips, motors).
|
||
|
||
***
|
||
|
||
## 12. Size, PCB layers, and mechanical constraints
|
||
|
||
- **Target size:**
|
||
- As **small and tiny as possible** to maximize space for the **battery** and wearable‑side components.
|
||
- Target in the range of **~20×30 mm** or smaller, depending on antenna and battery constraints.
|
||
- **PCB stack‑up:**
|
||
- Use **single‑sided PCB** where possible.
|
||
- If routing density or RF layout requires it, switch to **double‑sided (2‑layer) PCB**.
|
||
- **Ground and RF:**
|
||
- Use a **solid ground plane** under RF and MCU sections.
|
||
- Follow Espressif’s ESP32‑S3 hardware design guidelines for antenna keep‑out and RF‑matching.
|
||
|
||
***
|
||
|
||
## 13. External power input and protection
|
||
|
||
- **External power input pads:**
|
||
- Provide **two dedicated solder pads** for **external input voltage**:
|
||
- `VIN` (or `VEXT`).
|
||
- Adjacent `GND` pad.
|
||
- **Voltage protection and regulation:**
|
||
- The external input must tolerate a **range above 3.3 V** (e.g., roughly 4–12 V, negotiable with the designer).
|
||
- Include:
|
||
- A **wide‑input buck regulator** (or similar) that steps higher input down to:
|
||
- A safe bus voltage for the **Li‑Po charger** (e.g., 4.5–5.5 V), and/or
|
||
- Directly to **3.3 V** for the MCU and peripherals.
|
||
- **Over‑voltage protection** (OVP) or a **TVS / ESD clamp** on the `VIN` line.
|
||
- **Behavior:**
|
||
- The board can be powered via:
|
||
- USB‑C.
|
||
- Or the external `VIN` pads.
|
||
- Only **one** power source should be active at a time.
|
||
- **Labeling:**
|
||
- Clearly mark the pads as:
|
||
- `VIN`
|
||
- `GND (VIN)`
|
||
|
||
***
|
||
|
||
## 14. Bill of Materials (BOM) draft
|
||
|
||
This is a **functional BOM**; the designer may substitute functionally equivalent parts (with your approval).
|
||
|
||
| ID | Function | Suggested / Example Part | Notes |
|
||
|----|----------|--------------------------|-------|
|
||
| MCU1 | Main MCU | ESP32‑S3‑WROOM‑32 / ESP32‑S3‑MINI | Wi‑Fi/BLE, USB‑UART, 45+ GPIOs |
|
||
| CHG1 | Li‑Po charger | TP4056 or similar modern Li‑Po charge IC | 5 V input, CHRG/DONE outputs |
|
||
| GAGE1 | Battery gauge | MAX1704x / MAX170xx family | I²C‑based SoC estimation |
|
||
| IMU1 | Motion sensor | ST **LSM6DSV80X** | 6‑axis, 16 g + 80 g accel, 2.5×3 mm |
|
||
| RTC1 | RTC module | Generic I²C 32‑kHz RTC with coin‑cell backup | Alarm / interrupt output |
|
||
| REG1 | 3.3 V main rail | 3.3 V buck converter (e.g., AP62x0x‑style) | 3.3 V @ 300–500 mA+ |
|
||
| BOOST1 | 5 V booster | 5 V boost converter with enable pin | Must be GPIO‑controllable |
|
||
| USB1 | USB‑C receptacle | Standard USB‑Type C SMD connector | Dual‑role (charging + programming) |
|
||
| USB_PROT1 | USB‑line protection | USB‑ESD array / 5‑V clamp | Protects D‑/D+ and VBUS |
|
||
| VIN_PROT1 | External input protection | Wide‑input buck (e.g., LM2576‑style or similar) plus TVS | Steps 4–12 V down to safe rail |
|
||
| OLED1 | OLED display connector | 4‑pin header / footprint | 3.3 V, GND, SDA, SCL |
|
||
| CRYST1 | 40 MHz / 32 kHz crystals | 40 MHz + 32.768 kHz (if required) | As per ESP32‑S3 / RTC requirements | |