PCB Design

1. Audio Amplifier

  • Function: This section of the PCB drives the output to the onboard speaker (22). It takes low-power audio signals and amplifies them to drive the speaker effectively.
  • Key Components:
    • IC: Likely a Class D or Class AB audio amplifier IC such as the MAX98357 or TPA3110, which are common choices for compact, efficient audio amplification.
    • Passive Components: Capacitors for filtering, resistors for gain control, and inductors (if using Class D) to smooth output.
  • Considerations: High efficiency and low distortion are critical for portable applications. If a Class D amplifier is used, it provides low power dissipation with minimal heat generation.

2. USB Sound Card

  • Function: Allows for audio I/O over a USB interface. This is commonly used to interface with external devices for sound recording or playback.
  • Key Components:
    • IC: A common USB audio codec, such as the PCM2900 or CM108B, which supports USB audio class.
    • Crystals: A 12 MHz crystal for USB clock generation.
    • Passives: Decoupling capacitors and resistors for proper signal integrity on the USB differential pairs (D+/D-).
  • Considerations: Proper grounding and USB data line routing are essential to prevent noise from affecting audio quality.

3. Battery Protection Circuit

  • Function: Protects the lithium-ion battery from overcharge, over-discharge, overcurrent, and short-circuit conditions.
  • Key Components:
    • IC: A battery protection IC such as BQ29700 for 1S or BQ76930 for 2-3 cell configurations.
    • MOSFETs: Used to control the disconnection of the battery in case of overvoltage or short-circuit.
    • Resistors and Capacitors: Sensing resistors for current detection, capacitors for noise filtering.
  • Considerations: Ensure the battery protection IC matches the chemistry and cell count of the battery pack (18650 cells). Low Rds(on) MOSFETs are selected to minimize voltage drop and heat.

4. Equalizing Charge

  • Function: Balances the charge between the cells of the battery pack (if more than one 18650 cell is used), ensuring that all cells charge to the same voltage.
  • Key Components:
    • IC: A battery balancer IC such as BQ29209 for cell balancing.
    • Shunt Resistors: Used to discharge cells that are overcharged relative to others.
  • Considerations: Critical for maintaining battery health and maximizing the lifespan of multi-cell battery packs.

5. Motherboard Power Supply (5A Maximum)

  • Function: Supplies regulated power (likely 5V, 3.3V) to all the components on the PCB. Supports up to 5A, which indicates high current loads, possibly from motors and other power-hungry components.
  • Key Components:
    • IC: Buck or boost converter IC such as LM2675 or TPS54331 for efficient power conversion.
    • Inductor: Used in switching power supplies for energy storage and filtering.
    • Capacitors: Electrolytic and ceramic capacitors for input/output voltage smoothing.
    • Diodes: Schottky diodes to handle the flyback in switch-mode power supplies.
  • Considerations: Ensure that thermal dissipation is well-managed. Use low ESR capacitors for stability and noise reduction. A heat sink might be required for high-load applications.

6. IMU Attitude Sensor

  • Function: Measures the 3D orientation, acceleration, and angular velocity of the system, crucial for motion tracking, stabilization, and navigation.
  • Key Components:
    • IC: Common IMUs include MPU-6050, ICM-20948, or LSM6DS3, which are six-axis (gyro + accelerometer) or nine-axis (gyro + accelerometer + magnetometer) sensors.
    • Crystals: May use a crystal for timing or rely on the system clock.
    • Resistors: Pull-up resistors on I2C lines for communication.
  • Considerations: Proper placement and vibration damping are important to ensure accurate measurements. Shielding might be necessary to avoid electromagnetic interference (EMI).

7. USB Hub

  • Function: Expands the USB capability by providing multiple USB ports to connect additional peripherals.
  • Key Components:
    • IC: A typical USB hub controller, such as FE1.1s or TUSB4041, which can handle multiple downstream USB ports.
    • Passives: Decoupling capacitors and termination resistors for signal integrity.
  • Considerations: Ensure proper routing of USB differential pairs, maintain impedance matching, and keep traces short to prevent signal degradation.

8. Raspberry Pi RP2040 Microcontroller

  • Function: Serves as the main processing unit of the PCB, handling data processing, control, and communication between various peripherals.
  • Key Components:
    • RP2040 SoC: Dual-core ARM Cortex-M0+ processors running at 133 MHz, with 264KB SRAM and a wide range of GPIO pins.
    • External Flash Memory: Typically, an 8MB QSPI flash for storing firmware and program data.
    • Decoupling Capacitors: Placed near the power pins to reduce noise and ensure stable operation.
  • Considerations: Adequate cooling and bypassing are essential. RP2040 supports a wide range of interfaces (I2C, SPI, UART) for easy expansion.

9. Motor Driver

  • Function: Controls the motors connected to the motor ports (23), allowing for speed, direction, and torque control.
  • Key Components:
    • IC: H-bridge motor driver IC such as L298N or more compact options like DRV8833.
    • MOSFETs: High-current MOSFETs might be used for switching high currents in PWM mode.
    • Diodes: Flyback diodes to protect the circuit from voltage spikes generated by inductive loads (the motor).
  • Considerations: Proper heat dissipation and current sensing for motor feedback are critical for robust operation.

10. Battery Voltage and Current Monitoring

  • Function: Monitors the voltage and current from the 18650 battery pack to ensure proper charging and discharging cycles.
  • Key Components:
    • IC: Battery monitoring IC such as INA219 for high-accuracy current and voltage sensing.
    • Shunt Resistors: Used for current sensing with minimal voltage drop.
    • Analog-to-Digital Converter (ADC): Converts the analog voltage/current values to digital signals for processing.
  • Considerations: Ensure the sense resistors are low enough to minimize power loss but still provide accurate measurements.

11. Dual MEMS Silicon Microphone

  • Function: Captures audio from the environment, typically for voice recognition or sound sensing.
  • Key Components:
    • IC: MEMS microphones such as SPH0645LM4H or ICS-43432, which convert sound waves into electrical signals.
    • Amplifiers: Pre-amplification might be required before sending the signal to the microcontroller or USB sound card.
  • Considerations: Placement of microphones is critical for noise isolation. Shielding from high-frequency signals will prevent interference.

12. Lidar Interface

  • Function: Interfaces with an external LIDAR sensor for distance measurement or object detection.
  • Key Components:
    • Connector: Likely a serial (UART, I2C) or SPI interface to communicate with the LIDAR sensor.
    • Resistors and Capacitors: Pull-ups for I2C lines, decoupling capacitors for noise reduction.
  • Considerations: Ensure the interface supports the specific communication protocol of the LIDAR sensor being used.

13. Lidar Power Switch

  • Function: Switches the power to the LIDAR sensor, allowing it to be turned on or off as needed to save power.
  • Key Components:
    • MOSFET: A low Rds(on) MOSFET for switching the LIDAR’s power supply.
    • Control Logic: Controlled by GPIO from the microcontroller or a dedicated power management IC.
  • Considerations: Ensure the MOSFET can handle the LIDAR’s power consumption and is efficient to minimize heat generation.

14. Charging Port

  • Function: Provides a charging interface for the onboard 18650 battery pack.
  • Key Components:
    • Connector: USB Type-C or Micro-USB for external power input.
    • IC: Battery charger IC, such as BQ24079, which supports lithium-ion charging.
    • Inductors and Capacitors: Used in conjunction with the charging IC to ensure stable

current and voltage regulation.

  • Considerations: The charging circuit should handle overvoltage protection and current limiting to safely charge the battery.

15. OLED Display

  • Function: Displays system information such as battery levels, status updates, or user interaction data.
  • Key Components:
    • Display Module: OLED screen with typical sizes of 128x64 pixels. Common driver ICs are SSD1306.
    • Interface: I2C or SPI for communication with the microcontroller.
    • Resistors: Pull-ups for the I2C lines if required.
  • Considerations: Ensure the display’s power consumption is managed, as OLED displays can draw significant current.

16. Pogo Pin

  • Function: Provides a temporary connection point for development, testing, or external modules.
  • Key Components: Pogo pin headers with spring-loaded connectors.
  • Considerations: Ensure strong mechanical stability and reliable contact for testing or programming.

17. Power Switch

  • Function: Powers the entire system on or off.
  • Key Components:
    • Switch: SPST (Single Pole Single Throw) or DPST switch for high-current loads.
    • MOSFET: Could be used in conjunction with a soft-start circuit to avoid inrush current.
  • Considerations: Rated for the total system power draw.

18. Reset Button

  • Function: Resets the microcontroller (RP2040) or the entire system.
  • Key Components: Momentary push-button connected to the reset line of the microcontroller.
  • Considerations: Debouncing the reset button to prevent accidental multiple resets.

19. Download Button

  • Function: Used to trigger the bootloader mode for firmware updates on the RP2040.
  • Key Components: Momentary switch tied to a GPIO or the BOOTSEL pin of the RP2040.
  • Considerations: Ensure proper pull-down resistors to avoid false triggering.

20. Type-C Connector

  • Function: Provides a modern USB interface for power and data transfer.
  • Key Components: USB Type-C connector.
  • Considerations: Ensure proper routing for the differential pairs (D+/D-) and use ESD protection diodes.

21. Speaker Volume Button

  • Function: Adjusts the output volume of the audio amplifier (1).
  • Key Components:
    • Potentiometer: Analog volume control or a digital potentiometer IC like the MCP4018.
  • Considerations: Ensure that it is accessible and well-calibrated to the audio amplifier’s input range.

22. Speaker

  • Function: Outputs sound driven by the audio amplifier.
  • Key Components: A small electromagnetic speaker or piezoelectric element.
  • Considerations: Match the impedance with the amplifier’s output for optimal performance.

23. Motor Ports

  • Function: Connects motors to the motor driver circuit.
  • Key Components: JST or similar connectors to ensure a secure connection.
  • Considerations: Ensure the motor driver IC can handle the voltage and current requirements of the connected motors.

24. 18650 Battery Holder

  • Function: Holds two 18650 cells that power the entire PCB.
  • Key Components: Spring-loaded battery holder.
  • Considerations: Ensure proper connection and safety measures, such as fuses, to prevent shorts or thermal runaway.