# 03: Compact Dense Square Audio & Motion Reactive Controller PCB ## Complete Hardware Architecture, Spatial Density Breakdown & Turnkey Assembly Guide --- ## 1. Executive Summary & Mechanical Envelope The **03-compactAudioMotionSquarePCB** is an ultra-dense, parametric square carrier board designed for compact interactive devices, wearable medallions, pocketable audio-visual gadgets, dynamic robotics, and enclosed props where an elongated baton cannot fit. * **Board Dimensions**: $38.0\,\text{mm} \times 38.0\,\text{mm} \times 1.6\,\text{mm}$ (FR4 standard 2-layer). * **Footprint Area**: $1444\,\text{mm}^2$ (~37% smaller footprint than Project 02's $2300\,\text{mm}^2$ baton, and a ~67% reduction in maximum bounding dimension from 115mm to 38mm). * **Back-to-Back 3D Component Stacking**: * **Top Surface**: ESP32-C3 SuperMini mounted slightly offset from center ($x = -2.5\,\text{mm}, y = 1.5\,\text{mm}$). * **Backside (Bottom Surface)**: Universal MPU-6050 / GY-521 8-pin vertical header mounted at $x = +9.0\,\text{mm}, y = 1.5\,\text{mm}$. * **Physical Clearance Math**: The distance between ESP32 right pin row ($+6.39\,\text{mm}$) and the IMU pin row ($+9.0\,\text{mm}$) is $2.61\,\text{mm}$ (> 100 mil). When plugged into the bottom header, the $15.6\,\text{mm} \times 20.5\,\text{mm}$ GY-521 board body extends across the backside toward the left ($x = +9.0$ to $-6.6\,\text{mm}$), resting directly underneath the ESP32 substrate with **zero pin collision**. * **Perimeter Ring Distribution**: * All user-accessible headers (3× addressable LED outputs, 2× haptic vibration motor outputs, MAX4466 analog microphone, INMP441 digital I2S microphone, boot mode button, battery dual solder pads, and external power switch) are arranged along the 4 outer edges of the square board. * **Standard 4-Corner M3 Mounting Pattern**: * 4× symmetric plated mounting holes with **Ø3.2mm clearance drill** and **Ø4.8mm copper annular ring pads**. Centered at $(\pm 15.5\,\text{mm}, \pm 15.5\,\text{mm})$, creating a standardized **$31.0\,\text{mm} \times 31.0\,\text{mm}$** mounting pattern compatible with electronics stacks, quadcopter frames, and 3D printed enclosures. * **Turnkey Factory Assembly (JLCPCB 1-to-1 BOM & CPL Parity)**: * Factory SMT pre-assembly of all 14 active & passive discrete parts: MCP73831 LiPo charger, auto power-path switching (AO3401A + SS14), inductive flyback haptic driver (AO3400A + SS14), and quiescent drain high-side LED cutoff (AO3401A + AO3400A pre-driver). --- ## 2. Hardware Architecture Block Diagram ``` +----------------------------------------------------------------------------------------------------------------+ | PROJECT 03 HARDWARE BLOCK DIAGRAM | | | | [ USB 5V In ] ----> [ D_PWR (SS14) ] ------------------------------+ | | | | | | | v v v | | [ U_CHG: MCP73831 ] [ Q_PWR Gate ] [ NET_VSYS Rail ] | | | | | | | | (500mA) v +----> [ ESP32-C3 MCU (Top Side) ] | | v [ Q_PWR (AO3401A) ] | (13 GPIO Channels Active) | | [ J_BAT (Dual) ] ----> Source -> Drain ----------------------------+ | | | | | | [ GPIO 10 (LED Power Enable) ] | | [ SW_EXT Switch ] | | | | | | | v | | [ Q_LED_PWR (AO3401A P-FET) ] <--- Source [ NET_VSYS ] | | [ Q_LED_EN: AO3400A N-FET ] | | | Drain | | [ R_LED_GATE: 10k Pull-Down ] | | v [ NET_5V_SW ] (Zero Quiescent Sleep) | | | | | +---------------------------------------------+ | +--------+ (P-FET Gate Driver) | | | | | | | [ R_LED_PU: 100k Pull-Up ] | | v v v | | | [ J_LED1 (Top) ] [ J_LED2 (Right) ] [ J_LED3 (Left) ] | [ J_BTN (Mode / Boot Pin) ] | | DATA: GPIO 6 DATA: GPIO 20 DATA: GPIO 21 | Pin 1: GPIO 9 (Internal Pull-Up) | | | Pin 2: GND | | [ Haptic PWM GPIO 7 ] ----> [ Q_FET: AO3400A ] <----+----+---------+----> [ J_HAP_L / J_HAP_R ] (Motors) | | [ R_GATE: 10k Pull ] | | | | | [ D_HAP: SS14 Flyback ] +----+ +----> [ MPU-6050 IMU (Backside) ] | | +----> [ INMP441 / MAX4466 Mics ] | +----------------------------------------------------------------------------------------------------------------+ ``` --- ## 3. Spatial Density & Nesting Math ### 3.1 Back-to-Back Layer Separation By mounting the ESP32-C3 SuperMini on the **top surface** and the GY-521 MPU-6050 breakout on the **backside**: 1. **Vertical Footprint Compression**: The two largest micro-modules occupy the **exact same $X/Y$ board area** on opposing faces of the 1.6mm FR4 core. 2. **Pin Clearance Without Overlap**: - ESP32-C3 SuperMini right row of pins is at $x = -2.5 + 8.89 = +6.39\,\text{mm}$. - MPU-6050 8-pin header is at $x = +9.0\,\text{mm}$. - Distance between rows: $9.0 - 6.39 = 2.61\,\text{mm}$. - Even if through-hole pins are trimmed to standard 1.5mm protrusion, there is zero risk of electrical short-circuit or physical pin collision. ### 3.2 Dual-Mount Hybrid Footprints Every connector (MCU 16-pin, IMU 8-pin, LEDs, Microphones, Haptics, and Battery Pads) features dual-mount pads: - **Plated Through-Hole (THT)**: $\varnothing 1.0\,\text{mm}$ drill with $\varnothing 1.8\,\text{mm}$ annular ring for high-vibration pin headers. - **Surface Mount (SMD)**: Overlapping rectangular solder pads ($1.6\,\text{mm} \times 1.6\,\text{mm}$) for flush surface soldering. --- ## 4. Turnkey SMT Bill of Materials (JLCPCB 1-to-1 Parity) | Item # | Designator | Component Description | Footprint | LCSC Part # | Qty | |---|---|---|---|---|---| | 1 | `U_CHG` | MCP73831T-2ACI/OT 500mA Linear Charger | SOT-23-5 | `C14878` | 1 | | 2 | `R_PROG` | 2.0 kΩ 1% 0603 Thick Film Resistor | 0603 | `C17975` | 1 | | 3 | `C_VIN` | 4.7 µF 10V X5R 0603 Ceramic Capacitor | 0603 | `C15849` | 1 | | 4 | `C_BAT` | 4.7 µF 10V X5R 0603 Ceramic Capacitor | 0603 | `C15849` | 1 | | 5 | `Q_PWR` | AO3401A -30V -4.0A P-Channel MOSFET | SOT-23 | `C15127` | 1 | | 6 | `D_PWR` | SS14 40V 1A Schottky Barrier Diode | SOD-123 | `C22452` | 1 | | 7 | `R_PWR` | 100 kΩ 5% 0603 Thick Film Resistor | 0603 | `C25803` | 1 | | 8 | `Q_FET` | AO3400A 30V 5.7A N-Channel MOSFET | SOT-23 | `C20917` | 1 | | 9 | `R_GATE` | 10 kΩ 5% 0603 Thick Film Resistor | 0603 | `C25804` | 1 | | 10 | `D_HAP` | SS14 40V 1A Schottky Flyback Diode | SOD-123 | `C22452` | 1 | | 11 | `Q_LED_PWR` | AO3401A -30V -4.0A P-Channel MOSFET | SOT-23 | `C15127` | 1 | | 12 | `Q_LED_EN` | AO3400A 30V 5.7A N-Channel MOSFET | SOT-23 | `C20917` | 1 | | 13 | `R_LED_PU` | 100 kΩ 5% 0603 Thick Film Resistor | 0603 | `C25803` | 1 | | 14 | `R_LED_GATE` | 10 kΩ 5% 0603 Thick Film Resistor | 0603 | `C25804` | 1 | --- ## 5. Summary of Key Achievements 1. Successfully compressed the circuit from 115mm down to 38mm. 2. Solved spatial collision by back-to-back 3D stacking of the ESP32 and MPU. 3. Preserved all 3 independent addressable LED channels, dual haptic drivers, dual microphones, and LiPo charging with automatic power-path switching. 4. Maintained 100% manufacturing parity with JLCPCB SMT guidelines.