Introduction to Encoders

Table of contents

1. Introduction to Encoders
   1. What is it?
   2. How Encoders Works
      1. Two DIO Ports
   3. Initializing Encoders
   4. Key Methods of Encoders
   5. Configuring Encoders
   6. Activity

What is it?

An encoder is a device that detects motion and generates an electrical signal to provide feedback on the position, speed, and direction of a system by converting physical movement into electrical pulses.

How Encoders Works

In the XRP Minibot, a type of encoder is used called a quadrature encoder, which uses two signals to track movement accurately.

Two DIO Ports

Pulse — A cycle of alternating high (with voltage) and low (no voltage) electrical signals.

Encoders connect to the robot’s control board using two Digital Input/Output (DIO) pins, labeled Channel A and Channel B. Pulses are sent to these channels and the timing and sequence of the high and low pulses help to provide information on position, speed, direction, etc. of a system.

Initializing Encoders

To use an encoder, you need to initialize it in your code by specifying the two DIO ports it is connected to. For example:

// Initializing an encoder connected to DIO ports 0 and 1
Encoder encoder = new Encoder(0, 1);

Key Methods of Encoders

Encoders offer several useful methods.

• getDistance():
  • Returns the total distance the robot has traveled, calculated by counting the pulses from the encoder.
• getRate():
  • Returns the minibot’s speed in distance per second based on the encoder’s pulse rate.
• getStopped():
  • Determine if the encoder is stopped.
• getDirection():
  • Returns the direction in which the encoder last moved
• get():
  • Returns the current pulse count from the encoder.
• reset():
  • Reset the Encoder distance to zero.

Configuring Encoders

These methods can be used to configure the encoders.

• setDistancePerPulse(double distancePerPulse):
  • Configures the encoder to return a specific distance for every pulse.
  • Example: setDistancePerPulse(4.0/256.0) sets the distance per pulse to 4 units for every 256 pulses.
• setMinRate():
  • Configures the encoder to consider movement stopped if the rate of movement drops below a certain threshold.

Activity

Look at the Drivetrain.java file located in the subsystems folder. How are encoders used in the Drivetrain subsystem?