ev3dev language bindings¶

Device (abstract)¶

class Device¶

This is the base class that handles control tasks for a single port or index. The class must chose one device out of the available ports to control. Given an IO port (in the constructor), an implementation should:

• If the specified port is blank or unspecified/undefined/null, the available devices should be enumerated until a suitable device is found. Any device is suitable when it’s type is known to be compatible with the controlling class, and it meets any other requirements specified by the caller.
• If the specified port name is not blank, the available devices should be enumerated until a device is found that is plugged in to the specified port. The supplied port name should be compared directly to the value from the file, so that advanced port strings will match, such as in1:mux3.

If an error occurs after the initial connection, an exception should be thrown by the binding informing the caller of what went wrong. Unless the error is fatal to the application, no other actions should be taken.

connected¶

If a valid device is found while enumerating the ports, the connected variable is set to true (by default, it should be false). If connected is false when an attempt is made to read from or write to a property file, an error should be thrown (except while in the consructor).

Motor¶

class Motor¶

The motor class provides a uniform interface for using motors with positional and directional feedback such as the EV3 and NXT motors. This feedback allows for precise control of the motors. This is the most common type of motor, so we just call it motor.

The way to configure a motor is to set the ‘_sp’ attributes when calling a command or before. Only in ‘run_direct’ mode attribute changes are processed immediately, in the other modes they only take place when a new command is issued.

ev3dev docs link: http://www.ev3dev.org/docs/drivers/tacho-motor-class/

System properties

Address¶

string, read

Returns the name of the port that this motor is connected to.

Command¶

string, write

Sends a command to the motor controller. See commands for a list of possible values.

Commands¶

string array, read

Returns a list of commands that are supported by the motor controller. Possible values are run-forever, run-to-abs-pos, run-to-rel-pos, run-timed, run-direct, stop and reset. Not all commands may be supported.

• run-forever will cause the motor to run until another command is sent.
• run-to-abs-pos will run to an absolute position specified by position_sp and then stop using the action specified in stop_action.
• run-to-rel-pos will run to a position relative to the current position value. The new position will be current position + position_sp. When the new position is reached, the motor will stop using the action specified by stop_action.
• run-timed will run the motor for the amount of time specified in time_sp and then stop the motor using the action specified by stop_action.
• run-direct will run the motor at the duty cycle specified by duty_cycle_sp. Unlike other run commands, changing duty_cycle_sp while running will take effect immediately.
• stop will stop any of the run commands before they are complete using the action specified by stop_action.
• reset will reset all of the motor parameter attributes to their default value. This will also have the effect of stopping the motor.

Count_Per_Rot¶

int, read

Returns the number of tacho counts in one rotation of the motor. Tacho counts are used by the position and speed attributes, so you can use this value to convert rotations or degrees to tacho counts. (rotation motors only)

Count_Per_M¶

int, read

Returns the number of tacho counts in one meter of travel of the motor. Tacho counts are used by the position and speed attributes, so you can use this value to convert from distance to tacho counts. (linear motors only)

Driver_Name¶

string, read

Returns the name of the driver that provides this tacho motor device.

Duty_Cycle¶

int, read

Returns the current duty cycle of the motor. Units are percent. Values are -100 to 100.

Duty_Cycle_SP¶

int, read/write

Writing sets the duty cycle setpoint. Reading returns the current value. Units are in percent. Valid values are -100 to 100. A negative value causes the motor to rotate in reverse.

Full_Travel_Count¶

int, read

Returns the number of tacho counts in the full travel of the motor. When combined with the count_per_m atribute, you can use this value to calculate the maximum travel distance of the motor. (linear motors only)

Polarity¶

string, read/write

Sets the polarity of the motor. With normal polarity, a positive duty cycle will cause the motor to rotate clockwise. With inversed polarity, a positive duty cycle will cause the motor to rotate counter-clockwise. Valid values are normal and inversed.

Position¶

int, read/write

Returns the current position of the motor in pulses of the rotary encoder. When the motor rotates clockwise, the position will increase. Likewise, rotating counter-clockwise causes the position to decrease. Writing will set the position to that value.

Position_P¶

int, read/write

The proportional constant for the position PID.

Position_I¶

int, read/write

The integral constant for the position PID.

Position_D¶

int, read/write

The derivative constant for the position PID.

Position_SP¶

int, read/write

Writing specifies the target position for the run-to-abs-pos and run-to-rel-pos commands. Reading returns the current value. Units are in tacho counts. You can use the value returned by counts_per_rot to convert tacho counts to/from rotations or degrees.

Max_Speed¶

int, read

Returns the maximum value that is accepted by the speed_sp attribute. This may be slightly different than the maximum speed that a particular motor can reach - it’s the maximum theoretical speed.

Speed¶

int, read

Returns the current motor speed in tacho counts per second. Note, this is not necessarily degrees (although it is for LEGO motors). Use the count_per_rot attribute to convert this value to RPM or deg/sec.

Speed_SP¶

int, read/write

Writing sets the target speed in tacho counts per second used for all run-* commands except run-direct. Reading returns the current value. A negative value causes the motor to rotate in reverse with the exception of run-to-*-pos commands where the sign is ignored. Use the count_per_rot attribute to convert RPM or deg/sec to tacho counts per second. Use the count_per_m attribute to convert m/s to tacho counts per second.

Ramp_Up_SP¶

int, read/write

Writing sets the ramp up setpoint. Reading returns the current value. Units are in milliseconds and must be positive. When set to a non-zero value, the motor speed will increase from 0 to 100% of max_speed over the span of this setpoint. The actual ramp time is the ratio of the difference between the speed_sp and the current speed and max_speed multiplied by ramp_up_sp.

Ramp_Down_SP¶

int, read/write

Writing sets the ramp down setpoint. Reading returns the current value. Units are in milliseconds and must be positive. When set to a non-zero value, the motor speed will decrease from 0 to 100% of max_speed over the span of this setpoint. The actual ramp time is the ratio of the difference between the speed_sp and the current speed and max_speed multiplied by ramp_down_sp.

Speed_P¶

int, read/write

The proportional constant for the speed regulation PID.

Speed_I¶

int, read/write

The integral constant for the speed regulation PID.

Speed_D¶

int, read/write

The derivative constant for the speed regulation PID.

State¶

string array, read

Reading returns a list of state flags. Possible flags are running, ramping, holding, overloaded and stalled.

Stop_Action¶

string, read/write

Reading returns the current stop action. Writing sets the stop action. The value determines the motors behavior when command is set to stop. Also, it determines the motors behavior when a run command completes. See stop_actions for a list of possible values.

Stop_Actions¶

string array, read

Returns a list of stop actions supported by the motor controller. Possible values are coast, brake and hold. coast means that power will be removed from the motor and it will freely coast to a stop. brake means that power will be removed from the motor and a passive electrical load will be placed on the motor. This is usually done by shorting the motor terminals together. This load will absorb the energy from the rotation of the motors and cause the motor to stop more quickly than coasting. hold does not remove power from the motor. Instead it actively tries to hold the motor at the current position. If an external force tries to turn the motor, the motor will ‘push back’ to maintain its position.

Time_SP¶

int, read/write

Writing specifies the amount of time the motor will run when using the run-timed command. Reading returns the current value. Units are in milliseconds.

Large Motor¶

class Large_Motor¶

EV3 large servo motor

inherits from: motor

Target driver(s): lego-ev3-l-motor

Medium Motor¶

class Medium_Motor¶

EV3 medium servo motor

inherits from: motor

Target driver(s): lego-ev3-m-motor

NXT Motor¶

class NXT_Motor¶

NXT servo motor

inherits from: motor

Target driver(s): lego-nxt-motor

Firgelli L12 50 Motor¶

class Firgelli_L12_50_Motor¶

Firgelli L12 50 linear servo motor

inherits from: motor

Target driver(s): fi-l12-ev3-50

Firgelli L12 100 Motor¶

class Firgelli_L12_100_Motor¶

Firgelli L12 100 linear servo motor

inherits from: motor

Target driver(s): fi-l12-ev3-100

DC Motor¶

class DC_Motor¶

The DC motor class provides a uniform interface for using regular DC motors with no fancy controls or feedback. This includes LEGO MINDSTORMS RCX motors and LEGO Power Functions motors.

ev3dev docs link: http://www.ev3dev.org/docs/drivers/dc-motor-class/

System properties

Address¶

string, read

Returns the name of the port that this motor is connected to.

Command¶

string, write

Sets the command for the motor. Possible values are run-forever, run-timed and stop. Not all commands may be supported, so be sure to check the contents of the commands attribute.

Commands¶

string array, read

Returns a list of commands supported by the motor controller.

Driver_Name¶

string, read

Returns the name of the motor driver that loaded this device. See the list of [supported devices] for a list of drivers.

Duty_Cycle¶

int, read

Shows the current duty cycle of the PWM signal sent to the motor. Values are -100 to 100 (-100% to 100%).

Duty_Cycle_SP¶

int, read/write

Writing sets the duty cycle setpoint of the PWM signal sent to the motor. Valid values are -100 to 100 (-100% to 100%). Reading returns the current setpoint.

Polarity¶

string, read/write

Sets the polarity of the motor. Valid values are normal and inversed.

Ramp_Down_SP¶

int, read/write

Sets the time in milliseconds that it take the motor to ramp down from 100% to 0%. Valid values are 0 to 10000 (10 seconds). Default is 0.

Ramp_Up_SP¶

int, read/write

Sets the time in milliseconds that it take the motor to up ramp from 0% to 100%. Valid values are 0 to 10000 (10 seconds). Default is 0.

State¶

string array, read

Gets a list of flags indicating the motor status. Possible flags are running and ramping. running indicates that the motor is powered. ramping indicates that the motor has not yet reached the duty_cycle_sp.

Stop_Action¶

string, write

Sets the stop action that will be used when the motor stops. Read stop_actions to get the list of valid values.

Stop_Actions¶

string array, read

Gets a list of stop actions. Valid values are coast and brake.

Time_SP¶

int, read/write

Writing specifies the amount of time the motor will run when using the run-timed command. Reading returns the current value. Units are in milliseconds.

Servo Motor¶

class Servo_Motor¶

The servo motor class provides a uniform interface for using hobby type servo motors.

ev3dev docs link: http://www.ev3dev.org/docs/drivers/servo-motor-class/

System properties

Address¶

string, read

Returns the name of the port that this motor is connected to.

Command¶

string, write

Sets the command for the servo. Valid values are run and float. Setting to run will cause the servo to be driven to the position_sp set in the position_sp attribute. Setting to float will remove power from the motor.

Driver_Name¶

string, read

Returns the name of the motor driver that loaded this device. See the list of [supported devices] for a list of drivers.

Max_Pulse_SP¶

int, read/write

Used to set the pulse size in milliseconds for the signal that tells the servo to drive to the maximum (clockwise) position_sp. Default value is 2400. Valid values are 2300 to 2700. You must write to the position_sp attribute for changes to this attribute to take effect.

Mid_Pulse_SP¶

int, read/write

Used to set the pulse size in milliseconds for the signal that tells the servo to drive to the mid position_sp. Default value is 1500. Valid values are 1300 to 1700. For example, on a 180 degree servo, this would be 90 degrees. On continuous rotation servo, this is the ‘neutral’ position_sp where the motor does not turn. You must write to the position_sp attribute for changes to this attribute to take effect.

Min_Pulse_SP¶

int, read/write

Used to set the pulse size in milliseconds for the signal that tells the servo to drive to the miniumum (counter-clockwise) position_sp. Default value is 600. Valid values are 300 to 700. You must write to the position_sp attribute for changes to this attribute to take effect.

Polarity¶

string, read/write

Sets the polarity of the servo. Valid values are normal and inversed. Setting the value to inversed will cause the position_sp value to be inversed. i.e -100 will correspond to max_pulse_sp, and 100 will correspond to min_pulse_sp.

Position_SP¶

int, read/write

Reading returns the current position_sp of the servo. Writing instructs the servo to move to the specified position_sp. Units are percent. Valid values are -100 to 100 (-100% to 100%) where -100 corresponds to min_pulse_sp, 0 corresponds to mid_pulse_sp and 100 corresponds to max_pulse_sp.

Rate_SP¶

int, read/write

Sets the rate_sp at which the servo travels from 0 to 100.0% (half of the full range of the servo). Units are in milliseconds. Example: Setting the rate_sp to 1000 means that it will take a 180 degree servo 2 second to move from 0 to 180 degrees. Note: Some servo controllers may not support this in which case reading and writing will fail with -EOPNOTSUPP. In continuous rotation servos, this value will affect the rate_sp at which the speed ramps up or down.

State¶

string array, read

Returns a list of flags indicating the state of the servo. Possible values are: * running: Indicates that the motor is powered.

LED¶

class LED¶

Any device controlled by the generic LED driver. See https://www.kernel.org/doc/Documentation/leds/leds-class.txt for more details.

System properties

Max_Brightness¶

int, read

Returns the maximum allowable brightness value.

Brightness¶

int, read/write

Sets the brightness level. Possible values are from 0 to max_brightness.

Triggers¶

string array, read

Returns a list of available triggers.

Trigger¶

string selector, read/write

Sets the led trigger. A trigger is a kernel based source of led events. Triggers can either be simple or complex. A simple trigger isn’t configurable and is designed to slot into existing subsystems with minimal additional code. Examples are the ide-disk and nand-disk triggers.

Complex triggers whilst available to all LEDs have LED specific parameters and work on a per LED basis. The timer trigger is an example. The timer trigger will periodically change the LED brightness between 0 and the current brightness setting. The on and off time can be specified via delay_{on,off} attributes in milliseconds. You can change the brightness value of a LED independently of the timer trigger. However, if you set the brightness value to 0 it will also disable the timer trigger.

Delay_On¶

int, read/write

The timer trigger will periodically change the LED brightness between 0 and the current brightness setting. The on time can be specified via delay_on attribute in milliseconds.

Delay_Off¶

int, read/write

The timer trigger will periodically change the LED brightness between 0 and the current brightness setting. The off time can be specified via delay_off attribute in milliseconds.

Button¶

class Button¶

Provides a generic button reading mechanism that can be adapted to platform specific implementations. Each platform’s specific button capabilites are enumerated in the ‘platforms’ section of this specification.

Sensor¶

class Sensor¶

The sensor class provides a uniform interface for using most of the sensors available for the EV3. The various underlying device drivers will create a lego-sensor device for interacting with the sensors.

Sensors are primarily controlled by setting the mode and monitored by reading the value<N> attributes. Values can be converted to floating point if needed by value<N> / 10.0 ^ decimals.

Since the name of the sensor<N> device node does not correspond to the port that a sensor is plugged in to, you must look at the address attribute if you need to know which port a sensor is plugged in to. However, if you don’t have more than one sensor of each type, you can just look for a matching driver_name. Then it will not matter which port a sensor is plugged in to - your program will still work.

ev3dev docs link: http://www.ev3dev.org/docs/drivers/lego-sensor-class/

System properties

Address¶

string, read

Returns the name of the port that the sensor is connected to, e.g. ev3:in1. I2C sensors also include the I2C address (decimal), e.g. ev3:in1:i2c8.

Command¶

string, write

Sends a command to the sensor.

Commands¶

string array, read

Returns a list of the valid commands for the sensor. Returns -EOPNOTSUPP if no commands are supported.

Decimals¶

int, read

Returns the number of decimal places for the values in the value<N> attributes of the current mode.

Driver_Name¶

string, read

Returns the name of the sensor device/driver. See the list of [supported sensors] for a complete list of drivers.

Mode¶

string, read/write

Returns the current mode. Writing one of the values returned by modes sets the sensor to that mode.

Modes¶

string array, read

Returns a list of the valid modes for the sensor.

Num_Values¶

int, read

Returns the number of value<N> attributes that will return a valid value for the current mode.

Units¶

string, read

Returns the units of the measured value for the current mode. May return empty string

I2C Sensor¶

class I2C_Sensor¶

A generic interface to control I2C-type EV3 sensors.

inherits from: sensor

Target driver(s): nxt-i2c-sensor

System properties

FW_Version¶

string, read

Returns the firmware version of the sensor if available. Currently only I2C/NXT sensors support this.

Poll_MS¶

int, read/write

Returns the polling period of the sensor in milliseconds. Writing sets the polling period. Setting to 0 disables polling. Minimum value is hard coded as 50 msec. Returns -EOPNOTSUPP if changing polling is not supported. Currently only I2C/NXT sensors support changing the polling period.

Power Supply¶

class Power_Supply¶

A generic interface to read data from the system’s power_supply class. Uses the built-in legoev3-battery if none is specified.

System properties

Measured_Current¶

int, read

The measured current that the battery is supplying (in microamps)

Measured_Voltage¶

int, read

The measured voltage that the battery is supplying (in microvolts)

Max_Voltage¶

int, read

Min_Voltage¶

int, read

Technology¶

string, read

Type¶

string, read

Lego Port¶

class Lego_Port¶

The lego-port class provides an interface for working with input and output ports that are compatible with LEGO MINDSTORMS RCX/NXT/EV3, LEGO WeDo and LEGO Power Functions sensors and motors. Supported devices include the LEGO MINDSTORMS EV3 Intelligent Brick, the LEGO WeDo USB hub and various sensor multiplexers from 3rd party manufacturers.

Some types of ports may have multiple modes of operation. For example, the input ports on the EV3 brick can communicate with sensors using UART, I2C or analog validate signals - but not all at the same time. Therefore there are multiple modes available to connect to the different types of sensors.

In most cases, ports are able to automatically detect what type of sensor or motor is connected. In some cases though, this must be manually specified using the mode and set_device attributes. The mode attribute affects how the port communicates with the connected device. For example the input ports on the EV3 brick can communicate using UART, I2C or analog voltages, but not all at the same time, so the mode must be set to the one that is appropriate for the connected sensor. The set_device attribute is used to specify the exact type of sensor that is connected. Note: the mode must be correctly set before setting the sensor type.

Ports can be found at /sys/class/lego-port/port<N> where <N> is incremented each time a new port is registered. Note: The number is not related to the actual port at all - use the address attribute to find a specific port.

System properties

Address¶

string, read

Returns the name of the port. See individual driver documentation for the name that will be returned.

Driver_Name¶

string, read

Returns the name of the driver that loaded this device. You can find the complete list of drivers in the [list of port drivers].

Modes¶

string array, read

Returns a list of the available modes of the port.

Mode¶

string, read/write

Reading returns the currently selected mode. Writing sets the mode. Generally speaking when the mode changes any sensor or motor devices associated with the port will be removed new ones loaded, however this this will depend on the individual driver implementing this class.

Set_Device¶

string, write

For modes that support it, writing the name of a driver will cause a new device to be registered for that driver and attached to this port. For example, since NXT/Analog sensors cannot be auto-detected, you must use this attribute to load the correct driver. Returns -EOPNOTSUPP if setting a device is not supported.

Status¶

string, read

In most cases, reading status will return the same value as mode. In cases where there is an auto mode additional values may be returned, such as no-device or error. See individual port driver documentation for the full list of possible values.

Touch Sensor¶

class Touch_Sensor¶

Touch Sensor

inherits from: sensor

Target driver(s): lego-ev3-touch, lego-nxt-touch

Special properties

Is_Pressed¶

boolean, read

A boolean indicating whether the current touch sensor is being pressed.

Required mode: TOUCH

Value index: 0

Color Sensor¶

class Color_Sensor¶

LEGO EV3 color sensor.

inherits from: sensor

Target driver(s): lego-ev3-color

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-ev3-color-sensor/

Special properties

Reflected_Light_Intensity¶

int, read

Reflected light intensity as a percentage. Light on sensor is red.

Required mode: COL-REFLECT

Value index: 0

Ambient_Light_Intensity¶

int, read

Ambient light intensity. Light on sensor is dimly lit blue.

Required mode: COL-AMBIENT

Value index: 0

Color¶

int, read

Color detected by the sensor, categorized by overall value.

• 0: No color
• 1: Black
• 2: Blue
• 3: Green
• 4: Yellow
• 5: Red
• 6: White
• 7: Brown

Required mode: COL-COLOR

Value index: 0

Red¶

int, read

Red component of the detected color, in the range 0-1020.

Required mode: RGB-RAW

Value index: 0

Green¶

int, read

Green component of the detected color, in the range 0-1020.

Required mode: RGB-RAW

Value index: 1

Blue¶

int, read

Blue component of the detected color, in the range 0-1020.

Required mode: RGB-RAW

Value index: 2

Ultrasonic Sensor¶

class Ultrasonic_Sensor¶

LEGO EV3 ultrasonic sensor.

inherits from: sensor

Target driver(s): lego-ev3-us, lego-nxt-us

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-ev3-ultrasonic-sensor/

Special properties

Distance_Centimeters¶

float, read

Measurement of the distance detected by the sensor, in centimeters.

Required mode: US-DIST-CM

Value index: 0

Distance_Inches¶

float, read

Measurement of the distance detected by the sensor, in inches.

Required mode: US-DIST-IN

Value index: 0

Other_Sensor_Present¶

boolean, read

Value indicating whether another ultrasonic sensor could be heard nearby.

Required mode: US-LISTEN

Value index: 0

Gyro Sensor¶

class Gyro_Sensor¶

LEGO EV3 gyro sensor.

inherits from: sensor

Target driver(s): lego-ev3-gyro

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-ev3-gyro-sensor/

Special properties

Angle¶

int, read

The number of degrees that the sensor has been rotated since it was put into this mode.

Required mode: GYRO-ANG

Value index: 0

Rate¶

int, read

The rate at which the sensor is rotating, in degrees/second.

Required mode: GYRO-RATE

Value index: 0

Infrared Sensor¶

class Infrared_Sensor¶

LEGO EV3 infrared sensor.

inherits from: sensor

Target driver(s): lego-ev3-ir

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-ev3-infrared-sensor/

Special properties

Proximity¶

int, read

A measurement of the distance between the sensor and the remote, as a percentage. 100% is approximately 70cm/27in.

Required mode: IR-PROX

Value index: 0

Sound Sensor¶

class Sound_Sensor¶

LEGO NXT Sound Sensor

inherits from: sensor

Target driver(s): lego-nxt-sound

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-nxt-sound-sensor/

Special properties

Sound_Pressure¶

float, read

A measurement of the measured sound pressure level, as a percent. Uses a flat weighting.

Required mode: DB

Value index: 0

Sound_Pressure_Low¶

float, read

A measurement of the measured sound pressure level, as a percent. Uses A-weighting, which focuses on levels up to 55 dB.

Required mode: DBA

Value index: 0

Light Sensor¶

class Light_Sensor¶

LEGO NXT Light Sensor

inherits from: sensor

Target driver(s): lego-nxt-light

ev3dev docs link: http://www.ev3dev.org/docs/sensors/lego-nxt-light-sensor/

Special properties

Reflected_Light_Intensity¶

float, read

A measurement of the reflected light intensity, as a percentage.

Required mode: REFLECT

Value index: 0

Ambient_Light_Intensity¶

float, read

A measurement of the ambient light intensity, as a percentage.

Required mode: AMBIENT

Value index: 0

Ports¶

INPUT_AUTO¶

Automatic input selection. Value is instance-specific (see below for details)

OUTPUT_AUTO¶

Automatic output selection. Value is instance-specific (see below for details)

INPUT_1¶

Sensor port 1, "in1"

INPUT_2¶

Sensor port 2,, "in2"

INPUT_3¶

Sensor port 3, "in3"

INPUT_4¶

Sensor port 4, "in4"

OUTPUT_A¶

Motor port A, "outA"

OUTPUT_B¶

Motor port B, "outB"

OUTPUT_C¶

Motor port C, "outC"

OUTPUT_D¶

Motor port D, "outD"