Circuit Schematics

Complete circuit diagrams for the Moto32 control unit, with detailed explanations of each functional block.

Download Schematics

Circuit Overview

The Moto32 circuit is divided into several functional blocks:

graph TB
    A[12V Battery Input] --> B[Power Supply<br/>Buck Converter]
    B --> C[ESP32-S3 Module<br/>Main MCU]
    A --> D[MOSFET Outputs<br/>8 Channels]
    C --> D
    E[USB-C Port] --> F[CH340C<br/>USB-UART]
    F --> C
    G[Protection<br/>TVS Diodes & Fuses] --> A
    C --> H[GPIO Expansion]

Power Supply Section

Input Power

12V Automotive Supply

Battery+ ──[Fuse]──[D1]──[C2]── 12V Rail
                              │
                              └── To Buck Converter (U3)
                              └── To MOSFET Sources

Components:

• Input Fuse: 10A recommended (external)
• D1 (SS34): Schottky diode for reverse polarity protection
  • Forward voltage: ~0.5V
  • Current rating: 3A
  • Protects circuit if battery connected backwards
• C2 (22µF): Input bulk capacitance
  • Filters battery noise
  • Smooths load transients

Buck Converter (3.3V Regulator)

AP63203WU-7 Step-Down Converter

12V ─┬─[U3: AP63203]─┬─ 3.3V @ 2A
     │               │
     └─[C10,C11]     └─[C4,C12]
        Input Cap       Output Cap

Key Specifications:

• Input voltage: 3.8V to 32V (handles automotive transients)
• Output voltage: 3.3V fixed
• Output current: Up to 2A
• Switching frequency: ~1.5MHz
• Efficiency: >90% typical at 12V input

Circuit Details:

• C10, C11: 22µF input capacitors (low ESR ceramic)
• C4, C12: 10µF output capacitors
• FB Network: Feedback resistors set output voltage
• SW Pin: Switching node (connect to inductor if external)

Protection Features:

• Thermal shutdown
• Output short-circuit protection
• Overcurrent limiting
• Under-voltage lockout (UVLO)

ESP32-S3 Module Section

MCU Module

ESP32-S3-WROOM-1-N8R2

              ┌─────────────────┐
     3.3V ────┤ VCC         GPIO│──── To MOSFETs
     GND  ────┤ GND      GPIO   │──── Inputs
    UART0 ────┤ TXD/RXD   GPIO  │──── I2C/SPI
     EN   ────┤ EN        GPIO   │──── Expansion
     BOOT ────┤ GPIO0     EN     │──── Enable
              └─────────────────┘

Power Supply:

• C1 (1µF): Primary decoupling capacitor (close to VCC pin)
• C3, C5-C9 (100nF): Additional decoupling
• R1 (10kΩ): Pull-up on EN (enable) pin

Programming Interface:

• R2 (100kΩ): Boot mode pull-up
• UART0: Connected to CH340C for USB programming
• GPIO0: Boot select (LOW = download mode)

Module Features:

• Dual-core Xtensa LX7 @ 240MHz
• 8MB Flash memory
• 2MB PSRAM
• Wi-Fi 802.11 b/g/n
• Bluetooth 5.0 LE
• 45x GPIO pins (many multiplexed)

GPIO Assignments

Default Pin Mapping:

USB Interface Section

USB-C Connector & CH340C

USB-to-Serial Bridge

USB-C ──[D4,D5]──┬── D+ ──[R20,R21]──┬── CH340C
                 │                    │
                 └── D- ──[R18,R19]──┘
                         
CH340C ──[TXD/RXD]── ESP32 UART0
       │
       └──[X1: 12MHz]── Crystal Oscillator

USB Protection:

• D4, D5 (SMBJ58A): TVS diodes on USB data lines
  • Clamp ESD transients to safe levels
  • Bidirectional protection
  • Fast response time (<1ps)

CH340C Circuit:

• U2 (CH340C): USB-to-UART converter IC
  • No external crystal needed (uses internal oscillator)
  • Automatic handshaking
  • 115200 baud default
• X1 (12MHz): External crystal for precise timing
  • Required for stable USB communication
  • ±50ppm tolerance

Serial Connection:

• TXD: CH340 transmit → ESP32 RXD
• RXD: CH340 receive → ESP32 TXD
• DTR/RTS: Automatic bootloader entry (if connected)

MOSFET Output Section

High-Side Switch Design

Each of the 8 outputs uses identical circuitry:

12V+ ────┬────────┬──── OUTPUT (to load)
         │        │
      [Source] [DMP4015SK3Q-13]
         │        │
      [Drain]     │
         │        │
     [Gate]───[R: 10kΩ]──── ESP32 GPIO
         │
        [R: 10kΩ]
         │
        GND

MOSFET: DMP4015SK3Q-13

Circuit Operation:

Output OFF (Default State):

• ESP32 GPIO: HIGH (3.3V) or FLOATING
• Gate pulled HIGH through 10kΩ resistor
• Gate-Source voltage: ~0V
• MOSFET: OFF (no conduction)
• Output: FLOATING (no voltage)

Output ON (Activated):

• ESP32 GPIO: LOW (0V)
• Gate pulled to GND through GPIO
• Gate-Source voltage: -12V
• MOSFET: FULLY ON (low resistance)
• Output: ~12V (battery voltage)

Gate Resistor (10kΩ):

• Limits gate current during switching
• Slows switching edge (reduces EMI)
• Provides default OFF state
• Acts as pull-up to 12V

Output Capabilities

Maximum Load Current:

Each output can safely handle:

• Continuous: ~5A (with adequate cooling)
• Peak: 10A (short duration)
• Fused: External 5-10A fuse per output recommended

Typical Motorcycle Loads:

Inductive Load Protection

Flyback Protection (Built-in):

MOSFETs have internal body diodes that provide flyback protection for inductive loads (relays, solenoids):

      OUTPUT
         │
    [Inductive Load]
         │
        GND
         
Internal Body Diode:
  - Clamps negative voltage spikes
  - Protects MOSFET from back-EMF
  - No external diode needed

For heavy inductive loads, external TVS diodes can be added across outputs for additional protection.

Protection Circuits

TVS Diodes

SMBJ58A Transient Voltage Suppressors

12V+ ────[D4]──── To Circuit
         │
        GND

USB D+ ──[D5]──┐
               │
USB D- ──[D5]──┤
               │
              GND

Specifications:

• Breakdown voltage: 58V nominal
• Clamping voltage: <94V @ 10A
• Peak pulse power: 600W
• Response time: <1ps

Protection Against:

• Load dump transients (alternator disconnect)
• Inductive kick-back from large loads
• ESD (electrostatic discharge)
• Ignition system noise
• Starter motor transients

Fuse Recommendations

Main Power Input:

• Rating: 10A fast-blow
• Type: Automotive blade fuse (ATO/ATC)
• Location: Inline near battery connection

Individual Output Fusing (Optional):

• Rating: 5-10A per output (match load)
• Type: Automotive mini blade fuse
• Benefit: Isolates fault to single output

Input Conditioning

Switch Inputs

Recommended circuit for handlebar switches:

3.3V ────[10kΩ]────┬──── GPIO Input
                   │
               [Switch]
                   │
                  GND

Features:

• Pull-up resistor provides default HIGH state
• Switch to GND for active LOW
• GPIO internal pull-ups can be used (20-50kΩ)
• Add 100nF capacitor for debouncing if needed

Input Protection:

For inputs exposed to vehicle electrical system:

12V Signal ──[10kΩ]──┬──[10kΩ]──── GPIO
                     │
                  [3.3V Zener]
                     │
                    GND

• Voltage divider reduces 12V to 3.3V safe levels
• Zener diode clamps overvoltage
• Series resistor limits current

Expansion Interfaces

I2C Bus

For adding sensors (IMU, temperature, etc.):

ESP32 SDA ──┬──[4.7kΩ]── 3.3V
            │
        [Sensor SDA]
            
ESP32 SCL ──┬──[4.7kΩ]── 3.3V
            │
        [Sensor SCL]

Common I2C Additions:

• IMU (lean angle sensor for turn signal auto-cancel)
• Temperature sensor (thermal monitoring)
• RTC (real-time clock for data logging)
• EEPROM (configuration storage)

SPI Bus

For high-speed peripherals:

• CAN bus transceivers
• SD card for logging
• External ADCs for analog inputs

CAN Bus (Future)

Planned addition for modern motorcycle communication:

ESP32 CAN_TX ──┬── CAN Transceiver ──┬── CAN_H
ESP32 CAN_RX ──┘   (e.g., MCP2551)   └── CAN_L

Applications:

• Read ECU data (RPM, temperature, errors)
• Communicate with ABS module
• Integrate with TFT dashboard
• Log vehicle data

PCB Traces & Grounding

Power Traces

Trace Width Calculations:

Ground Strategy

Multi-point grounding:

• Separate analog and digital grounds at PCB level
• Single point connection at power supply
• Ground planes on inner layers
• Via stitching for low impedance

Ground Loops Prevention:

• Star grounding for power
• Avoid ground loops in signal paths
• Keep high current returns separate

Reading the Schematic

Component Designators

Net Names

Common net naming in schematic:

• VCC / 3V3: 3.3V power rail
• 12V / VBAT: 12V battery input
• GND: Ground / 0V reference
• OUTx: MOSFET output channels
• INx: GPIO input channels

Design Calculations

Power Dissipation

Buck Converter:

Input Power = 12V × 0.5A = 6W
Output Power = 3.3V × 1.5A = 4.95W
Efficiency = 4.95W / 6W = 82.5%
Heat = 6W - 4.95W = 1.05W

MOSFET Losses:

Per MOSFET @ 5A load:
RDS(on) = 45mΩ
Power = I² × R = 5² × 0.045 = 1.125W

Schematic Checklist

When reviewing or modifying the schematic:

• All ICs have decoupling capacitors
• Power supply properly rated for load
• Protection diodes oriented correctly
• MOSFET source/drain connections correct
• Pull-up/pull-down resistors on all inputs
• No floating inputs or outputs
• Ground connections complete
• Fusing adequate for loads
• Component ratings exceed requirements
• Test points for critical signals

Next Steps