Encoder Component

An encoder is a type of sensor that can detect speed and direction of rotation of a motor or a joint. It is often used in conjunction with a motor, and is sometimes even built into a motor. An encoder could also be mounted on a passive joint or other rotating object to keep track of the joint angle.

The encoder component supports:

  • Incremental encoders, which can measure the speed and direction of rotation in relation to a given reference point like a starting point. These encoders output two phases. Based on the sequence and timing of these phases, it is determined how far something has turned and in which direction. Each phase output goes to a different pin on the board.
  • Single phase or single pin “pulse output” encoders, which measure the position relative to the starting position but not the direction.
  • Absolute encoders, which provide the absolute position of a rotating shaft, without requiring a reference point.

Most machines with an encoder need at least the following hardware:

  • A board component that can run a viam-server instance. For example, a Raspberry Pi, or another model of single-board computer with GPIO (general purpose input/output) pins.
  • Some sort of rotary machine part (like a motor, joint or dial) for which you want to measure movement.

Supported models

To use your encoder with Viam, check whether one of the following built-in models supports your encoder.

Built-in models

For configuration information, click on the model name:

ModelDescription
AMS-AS5048The AMS-AS5048 encoder is an absolute encoder that which can connect using an I2C interface.
fakeAn encoder model for testing.
incrementalA two phase encoder, which can measure the speed and direction of rotation in relation to a given reference point.
singleA single pin “pulse output” encoder which returns its relative position but no direction.

Micro-RDK

If you are using the micro-RDK, navigate to Micro-RDK Encoder for supported model information.

Control your encoder with Viam’s client SDK libraries

To get started using Viam’s SDKs to connect to and control your machine, go to your machine’s page on the Viam app, navigate to the Code sample tab, select your preferred programming language, and copy the sample code generated.

When executed, this sample code will create a connection to your machine as a client. Then control your machine programmatically by adding API method calls as shown in the following examples.

These examples assume you have an encoder called "my_encoder" configured as a component of your machine. If your encoder has a different name, change the name in the code.

Be sure to import the encoder package for the SDK you are using:

from viam.components.encoder import Encoder
import (
  "go.viam.com/rdk/components/encoder"
)

API

The encoder component supports the following methods:

Method NameDescription
GetPositionGet the current position of the encoder.
ResetPositionReset the position to zero.
GetPropertiesGet the supported properties of this encoder.
GetGeometriesGet all the geometries associated with the encoder in its current configuration, in the frame of the encoder.
DoCommandSend or receive model-specific commands.
CloseSafely shut down the resource and prevent further use.

GetPosition

Get the current position of the encoder in ticks or degrees. Relative encoders return ticks since last zeroing. Absolute encoders return degrees.

Parameters:

  • position_type (Optional[PositionType.ValueType]): Specify whether to get the current position in ticks (encoder.PositionTypeTicks) or in degrees (encoder.PositionTypeDegrees). If you are not sure which position type your encoder supports but it is a built-in Viam-supported model, you can leave this parameter unspecified (encoder.PositionTypeUnspecified) or empty and it will default to the correct position type.
  • extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
  • timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

For more information, see the Python SDK Docs.

my_encoder = Encoder.from_robot(robot=robot, name='my_encoder')

# Get the position of the encoder in ticks
position = await my_encoder.get_position(encoder.PositionTypeTicks)
print("The encoder position is currently ", position[0], position[1])

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
  • positionType (PositionType): Specify whether to get the current position in ticks (encoder.PositionTypeTicks) or in degrees (encoder.PositionTypeDegrees). If you are not sure which position type your encoder supports but it is a built-in Viam-supported model, you can leave this parameter unspecified (encoder.PositionTypeUnspecified) and it will default to the correct position type.
  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

  • (float64): The current position in ticks or degrees.
  • (PositionType): The type of position the encoder returns (ticks or degrees).
  • (error): An error, if one occurred.

For more information, see the Go SDK Docs.

myEncoder, err := encoder.FromRobot(robot, "my_encoder")
if err != nil {
  logger.Fatalf("cannot get encoder: %v", err)
}

// Get the position of the encoder in ticks
position, posType, err := myEncoder.Position(context.Background(), encoder.PositionTypeTicks, nil)

ResetPosition

Set the current position of the encoder to be the new zero position.

Parameters:

  • extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
  • timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

  • None

For more information, see the Python SDK Docs.

my_encoder = Encoder.from_robot(robot=robot, name='my_encoder')

# Reset the zero position of the encoder.
await my_encoder.reset_position()

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

  • (error): An error, if one occurred.

For more information, see the Go SDK Docs.

myEncoder, err := encoder.FromRobot(robot, "my_encoder")
if err != nil {
  logger.Fatalf("cannot get encoder: %v", err)
}

err := myEncoder.ResetPosition(context.Background(), nil)

GetProperties

Get a list of all the position types that are supported by a given encoder.

Parameters:

  • extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
  • timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

  • (Properties): The position types supported by the encoder model.

For more information, see the Python SDK Docs.

my_encoder = Encoder.from_robot(robot=robot, name='my_encoder')

# Get whether the encoder returns position in ticks or degrees.
properties = await my_encoder.get_properties()

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

For more information, see the Go SDK docs.

myEncoder, err := encoder.FromRobot(robot, "my_encoder")

// Get whether the encoder returns position in ticks or degrees.
properties, err := myEncoder.Properties(context.Background(), nil)

GetGeometries

Get all the geometries associated with the encoder in its current configuration, in the frame of the encoder. The motion and navigation services use the relative position of inherent geometries to configured geometries representing obstacles for collision detection and obstacle avoidance while motion planning.

Parameters:

  • extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
  • timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

For more information, see the Python SDK Docs.

my_encoder = Encoder.from_robot(robot=robot, name="my_encoder")

geometries = await my_encoder.get_geometries()

if geometries:
    # Get the center of the first geometry
    print(f"Pose of the first geometry's centerpoint: {geometries[0].center}")

DoCommand

Execute model-specific commands that are not otherwise defined by the component API. If you are implementing your own encoder as a modular resource and are adding features that have no built-in API method, you can access them with DoCommand.

Parameters:

Returns:

my_encoder = Encoder.from_robot(robot=robot, name='my_encoder')

reset_dict = {
  "command": "reset",
  "example_param": 30
}
do_response = await my_encoder.do_command(reset_dict)

For more information, see the Python SDK Docs.

Parameters:

Returns:

myEncoder, err := encoder.FromRobot(robot, "my_encoder")

resp, err := myEncoder.DoCommand(ctx, map[string]interface{}{"command": "reset", "example_param": 30})

For more information, see the Go SDK Code.

Close

Safely shut down the resource and prevent further use.

Parameters:

  • None

Returns:

  • None
my_encoder = Encoder.from_robot(robot, "my_encoder")

await my_encoder.close()

For more information, see the Python SDK Docs.

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.

Returns:

  • (error) : An error, if one occurred.
myEncoder, err := encoder.FromRobot(robot, "my_encoder")

err := myEncoder.Close(ctx)

For more information, see the Go SDK Docs.

Troubleshooting

You can find additional assistance in the Troubleshooting section.

You can also ask questions on the Viam Community Slack and we will be happy to help.

Next steps