Continuous Servo Control PCB

Overview

This project was an extension of my ENPH 259 final project, where I designed and built a custom circuit and PCB to control a continuous-rotation servo motor.

The goal was to replace the internal control electronics of a hobby servo with a standalone, feedback-stabilized driver that could be powered externally and provide smoother, more accurate speed control.

My Contributions

• Designed the full control circuit in KiCad, including feedback, comparator, and MOSFET driver stages.
• Created the PCB layout, ensuring signal integrity between the digital counting stages and the analog PI controller.
• Assembled and tested the board, debugging issues with clock timing and feedback resolution.
• Integrated the motor with a mechanical disk encoder to generate feedback signals.

Technical Highlights

• Speed Feedback: A slotted encoder disk generated pulses, which were counted and latched to represent motor speed in binary.
• Digital-to-Analog Conversion: The binary counter output was fed into an R-2R DAC, producing an analog voltage proportional to measured speed.
• Reference Comparison: A comparator compared the measured speed voltage against a reference input.
• Control Loop: A PI (proportional–integral) controller smoothed the error signal and stabilized speed regulation.
• Output Stage: The processed control voltage drove a MOSFET H-bridge to power the DC motor.
• Inputs/Outputs: The system required ±5 V, ground, and a 5 Hz clock signal to operate.

GitHub

github.com/georgesleen/continous-servo-pcb

Media

• PCB layout render
  

• Assembled board with servo
  

• Schematic (page 1)
  

• PCB front (page 1)
  

• Lab setup screenshot
  

Reflection

This project was my first time designing a complete closed-loop motor control system in hardware. It forced me to combine digital counting and DAC conversion with analog PI control, all integrated on a custom PCB.

Through this build, I gained practical experience in:

• PCB layout for mixed digital/analog systems
• Debugging timing and feedback issues
• Designing a control loop that balances responsiveness with stability

The final system successfully demonstrated that a low-cost servo can be transformed into a continuously controllable actuator using custom electronics.