PCB DESIGN REQUIREMENTS (FINAL – MECHANICAL CONSTRAINT UPDATED) 1. BOARD OVERVIEW (UPDATED) PCB Type: Main controller PCB (production-grade) Board Width: 100 mm (FIXED – DO NOT CHANGE) Board Length: Variable – minimize as per component layout Thickness: 1.6 mm Layers: 4-layer PCB (mandatory) L1: Signals L2: Solid GND plane L3: 5V power plane L4: Signals Solder Mask: Matte black Silkscreen: White Board Edge: Black Mounting Holes: 4 × M3 (corner-aligned to final outline) ⚠️ Mechanical Priority: PCB length reduction is a design objective, provided electrical safety, thermal margin, and connector accessibility are not compromised. 2. POWER SYSTEM Power Input Voltage: 5V DC Current: Up to 10A Connector: 2-pin screw terminal (5.08 mm) Protection (mandatory): Reverse polarity protection Polyfuse / blade fuse TVS diode Power Rails 5V: Servos, PCA9685, TMC2209 motor power 3.3V: ESP32, DS3231 RTC 3.3V Regulator: ≥600 mA (buck or LDO) 3. MICROCONTROLLER Module: ESP32-WROOM-32 Wi-Fi: Primary control Reset / Boot: EN + IO0 routed to UART socket 4. SERVO CONTROL SYSTEM (LOCKED) Drivers IC: PCA9685 Qty: 4 Interface: I²C Outputs Total Servos: 40 Zones (silkscreen mandatory): Zone 1–4 (10 servos each) Servo Connector (FINAL & SAVED) Type: JST-XH Pins: 3 Lock: Friction-lock Pitch: 2.54 mm Mount: Vertical, through-hole Pinout: GND +5V PWM Power Layout Rules ≥80 mil equivalent 5V copper ≥470 µF bulk capacitor per zone Star-routed servo power 5. STEPPER MOTOR SYSTEM Driver: TMC2209 (×2) Mode: STEP / DIR UART: Required Motor: NEMA 8 (5V) Motor Connector: JST-XH 4-pin Thermal: Copper pour + vias under driver 6. REAL-TIME CLOCK IC: DS3231 Voltage: 3.3V Backup: CR2032 holder Bus: Dedicated I²C (GPIO 32, 33) 7. USER INTERFACE (LOCKED) Push Button: 1 only Function: Reset / manual mode Status LED: 1 × Addressable RGB (WS2812) 8. PROGRAMMING & DEBUG (LOCKED) Connector: UART socket / header Pins: TX, RX, GND, 3.3V (optional) USB Connector: ❌ Not used Auto-boot: EN + IO0 routed 9. LAYOUT & EMI RULES Solid uninterrupted GND plane Servo power routed away from ESP32 antenna Separate routing for: Servo PWM Stepper STEP/DIR Onboard I²C pull-ups (~4.7 kΩ) Bulk caps close to load zones 10. SILKSCREEN & MARKINGS RC1 Controller Board PCB revision ZONE 1–4 labels Power polarity UART pin labels 11. MANUFACTURING DELIVERABLES Designer must supply: Schematic (PDF) PCB layout source files Gerbers Pick & Place BOM with MPNs 3D renders