Falcon Flight Stick

A custom-designed flight control stick for the Falcon Aircraft project — designing both hardware and firmware for force sensing, CAN communication, and USB HID joystick interfacing.

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Overview

The Falcon Flight Stick is a force-sensing joystick that measures user input via strain gauges and communicates with the aircraft’s control system through CAN bus or to a computer host via USB-C.
This project demonstrates my ability to proficiently design, route, and program an embedded system from the ground up — including power delivery, signal integrity, and firmware architecture.

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Key Features

• MCU Core: STM32F103CBU6 managing all board-level events with an external 8Mhz Oscillator
• Sensing System: Three strain gauges read via a precision Texas Instruments ADS131M03IRUK ADC (32-bit SPI interface)
• Connectivity:
  • USB-C (HID joystick or virtual COM port)
  • CAN bus daisy-chain communication
• Memory: 1×128-byte EEPROM for calibration data
• Power System:
  • TI TPS62177 step-down converter for higher current ditial power
  • ADI LT1962 LDO (3.3V) for low noise, low current analog power
  • Automatic protection between USB-C and LiPo (12V) sources
• PCB Stackup: 4-layer board with separated analog/digital planes for signal integrity
• Breakout Button Matrix:
  • button matrix allowing for a hotswappable and fully customizable button interface on the joystick
  • Up to 25 individual buttons, all allowable for interrupts

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Hardware Design

Hardware Repository

The latest hardware version is Falcon Flight Stick Rev5.
Previous revisions were experimental or undocumented.

Design Breakdown

The STM32 MCU is programmed through ST-LinkV3 (SWD) and communicates via UART for debug and development.
Differential USB data lines enable HID or COM functionality, depending on firmware.

Strain gauge signals are processed through a TI ADC, which triggers SPI reads via a DRDY interrupt.
Processed values are sent to the servo controller board (via CAN) or USB interface.

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Power Architecture

The power subsystem ensures stable operation from multiple sources:

• 12V LiPo (CAN chain) or 5V USB-C
• Both inputs are protected from backfeed
• Outputs:
  • 3.3V Digital (MCU, logic)
  • 3.3V Analog (ADC, strain gauge front-end)

These rails are physically isolated to minimize noise and ground-reference drift.

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Schematics

Full schematic set:

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PCB Layout

Summary

• 4-layer stackup for power and noise isolation
• Separated analog/digital ground and power planes
• Power trace widths sized by current draw
• Labelled parts for developer readability

Views

Full Layout:

Layer 1: Signal

Layer 2: Power

Layer 3: GND / AGND

Layer 4: Signal 2

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3D Model

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Firmware (Planned / In Progress)

Example outline:

• USB HID joystick emulation via STM32 HAL
• CAN message handling for actuator control
• ADC data acquisition and digital filtering
• EEPROM calibration storage

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Tools Used

• KiCad 8.0 – PCB and schematic design
• STM32CubeIDE – Firmware development & MCU pinout planning
• JLCPCB – Fabrication and assembly
• SolidWorks – 3D mechanical integration
• GitHub / Git – Version control

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