Interfacing TI Microcontrollers with Quadrature Encoders

Introduction

• Focus on decoding quadrature signals from optical and incremental encoders into position and movement info.
• Mentioned motor control briefly for context; not detailed herein.

What is an Encoder?

• Encoders: Mechanical devices attached to motors/rotors; encode position, direction, speed into pulses.
• Types of sensing: mechanical, magnetic, optical, electromagnetic.
• Two types:
  • Absolute Encoders: Encode absolute position.
  • Incremental Encoders (Quadrature Encoders): Describe position changes incrementally.

Timers and Quadrature Encoders

• Timers decode quadrature signals to derive speed, direction, position.
• Signals fed into microcontrollers measure period and frequency.
• Specialized timer modules: Quadrature Encoder Pulses or Interfaces.
• Applications: Sensor-based motor control, robotics.

Optical Quadrature Encoders

• Composed of a disk with opaque/transparent slots (encoder resolution).
• Light source and photosensors create pulse signals.
• Phase difference in pulses creates quadrature signals.
• Channels A and B offset by 90°, used to decode position, direction, speed.

Demonstration of Quadrature Signals

• Clockwise movement: Channel A leads B.
• Counterclockwise: Channel B leads A.
• Quadrature Index: Reference point, aids in position verification.

Decoding Quadrature Signals

• Timer module in capture mode tracks signal edges and frequency.
• Quadrature Decoder:
  • Generates clock and direction signals.
  • Direction based on channel transitions (illegal transition = error interrupt).
  • Clock sampled from edges for resolution.

Position Counter

• Tracks incremental position based on quadrature clock.
• Increments past max resets to zero; decrements below zero resets to max.
• Index resets position counter to mitigate drift.

Quadrature Decoder and Position Counter

• Position counter operations at 4x frequency of inputs.
• Example: Encoder with 44 slots; max position = 175.
• Position increments/decrements with direction signal.

Calculating Rotational Speed

• Velocity proportional to quadrature waveform frequency.
• Velocity equation: Frequency of waveforms and encoder resolution.
• Example calculation for a 1000-slot encoder: 1000 RPM.

Conclusion

• Overview of interfacing with Quadrature Encoders.
• References for further information and labs.