Interfacing TI Microcontrollers with Quadrature Encoders

Introduction

• Purpose: Review how timers can decode quadrature signals into position and movement information.
• Scope: Focus on optical incremental encoders, mentions motor control concepts for context.

Encoders Overview

• Definition: Mechanical devices that encode information like position, direction, speed into pulses interpretable by microcontrollers.
• Types: Sensing Techniques
  • Mechanical, magnetic, optical, electromagnetic.
• Types: Measurement
  • Absolute Encoders: Encode absolute position, known from power up.
  • Incremental Encoders (Quadrature): Encode position changes relative to a reference point.

Interfacing with Microcontrollers

• Timers Usage: Interface with quadrature encoders to derive movement data (speed, direction, position).
• Signal Decoding: Feed signals into microcontrollers to measure period and frequency.
• Modules: Some microcontrollers have specialized timers for quadrature encoders.
  • Known as quadrature encoder pulses/interfaces.

Optical Quadrature Encoder

• Components:
  • Disk with opaque/transparent slots (encoder resolution).
  • Light source and photosensors.
• Functioning:
  • Light passes through transparent slots; photosensors detect the light/dark pattern, producing quadrature signals.
  • Quadrature Signals: Two channels (A & B) offset by 90°, generating rotational info.

Quadrature Signal Analysis

• Clockwise Movement: Channel A leads B.
• Counterclockwise Movement: Channel B leads A.
• Quadrature Index: Marks zero/reference position, aids in monitoring and verification.

Signal Decoding Process

• Timer Module Configuration:
  • Capture mode to record signal edges and frequencies.
• Quadrature Decoder Function:
  • Decode waveforms into direction and clock signals for position tracking.
• State Machine:
  • Determines direction; prevents illegal transitions, triggering error interrupts.
• Position Counter:
  • Increments/Decrements based on direction signal.
  • Resets on reaching max/min position or index signal.

Demonstration Insights

• Position Counter and Signals:
  • Encoder with 44 slots: max position = 175.
  • Position increments clockwise and resets at index pulse.
  • Decrements counterclockwise, resets at index pulse.

Velocity Calculation

• Proportionality: Velocity is proportional to quadrature waveform frequency.
• Equation: Based on frequency and encoder resolution.
• Example: 1000 slot encoder at 16.667 kHz results in ~1000 RPM.

Conclusion

• Resources: More information and hands-on labs linked for further exploration.
• Thanks: End of training video.