Portable CD Player

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Portable CD Player



The Coby portable CD player is designed to read audio CDs and convert the disk's digital information to analog, electric signals. The signals are transmitted, via the headphone jack, to a set of headphones so that the user can listen to the audio track. Various user interfaces including control-buttons and visual displays permit the user to interact with the CD player.

Design Considerations

  • must play audio CDs
  • must output audio with satisfactory quality
  • must respond properly and quickly to user commands
  • must use a standard headphone jack for user-selected headphones
  • must use standard batteries for low cost and convienience


  • Human-Machine Interface
    • Input buttons to control the unit
    • LCD screen to provide information to the user
    • Volume knob to control output audio signal


  • Sensing
    • Cover Sensor - contact switch - allows CD player to 'know' when the cover is opened. The CD automatically stops if the cover is opened.
    • Laser Transport Home Sensor - contact switch - allows the Laser Transport to be 'homed' when the CD player is started. This ensures that the disk will be read from the beginning and that the transport will not crash into its mechanical limits of motion.
    • CD Speed Sensor - the CD player's processor uses feedback from the laser to accelerate or decelerate the CD to combat skipping.

Limit switches.jpg

  • Movements & Actuation
    • CD Spindle Motor - DC motor - rotates the CD
    • Laser-Transport Motor - DC motor - moves the Laser Transport radially along the CD
    • Laser-Focus Motor - Electromagnetic solenoid - moves the Laser assembly towards or away from the surface of the CD

  • Power Supply
    • Two 'AA' batteries supply power to the CD player. Unlike some higher-end portable CD players that include adapters to use 'wall power' (120 VAC), this player can only be powered by batteries.

  • Power & Motion Conversion
    • Gearing on the Laser-Transport Motor reduces the system's rotational speed while increasing its torque. The low-speed, high-torque output drives a feed-screw. The feed-screw converts rotary motion into the linear motion of the Laser Transport.


  • Intelligence
    • Data conversion from the CD's encoded information to an electronic output signal
    • Data conversion from the user input buttons to specific system responses