Essential Hub

../_images/hub-essential.png

../_images/pybricks_variables_set_essential_hub_option0.svg

../_images/pybricks_variables_set_essential_hub_option4.svg

class EssentialHub(top_side=Axis.Z, front_side=Axis.X, broadcast_channel=0, observe_channels=[])

LEGO® SPIKE Essential Hub.

Initializes the hub. Optionally, specify how the hub is placed in your design by saying in which direction the top side (with the button) and the front side (with the USB port, and I/O ports A and B) are pointing.

Parameters:
  • top_side (Axis) – The axis that passes through the top side of the hub.

  • front_side (Axis) – The axis that passes through the front side of the hub.

  • broadcast_channel – A value from 0 to 255 indicating which channel hub.ble.broadcast() will use. Default is channel 0.

  • observe_channels – A list of channels to listen to when hub.ble.observe() is called. Listening to more channels requires more memory. Default is an empty list (no channels).

Changed in version 3.3: Added broadcast_channel and observe_channels arguments.

Using the hub status light

../_images/pybricks_blockLightOnColor_essentialhub_on.svg

light.on(color)

Turns on the light at the specified color.

Parameters:

color (Color) – Color of the light.

../_images/pybricks_blockLightOnColor_essentialhub_off.svg

light.off()

Turns off the light.

Blinks the light at a given color by turning it on and off for given durations.

The light keeps blinking indefinitely while the rest of your program keeps running.

This method provides a simple way to make basic but useful patterns. For more generic and multi-color patterns, use animate() instead.

Parameters:
  • color (Color) – Color of the light.

  • durations (list) – Sequence of time values of the form [on_1, off_1, on_2, off_2, ...].

light.animate(colors, interval)

Animates the light with a sequence of colors, shown one by one for the given interval.

The animation runs in the background while the rest of your program keeps running. When the animation completes, it repeats.

Parameters:
  • colors (list) – Sequence of Color values.

  • interval (Number, ms) – Time between color updates.

Using the button

../_images/pybricks_blockButtonIsPressed_EssentialHub.svg

buttons.pressed() Set[Button]

Checks which buttons are currently pressed.

Returns:

Set of pressed buttons.

system.set_stop_button(button)

Sets the button or button combination that stops a running script.

Normally, the center button is used to stop a running script. You can change or disable this behavior in order to use the button for other purposes.

Parameters:

button (Button) – A button such as Button.CENTER, or a tuple of multiple buttons. Choose None to disable the stop button altogether.

Using the IMU

imu.ready() bool

Checks if the device is calibrated and ready for use.

This becomes True when the robot has been sitting stationary for a few seconds, which allows the device to re-calibrate. It is False if the hub has just been started, or if it hasn’t had a chance to calibrate for more than 10 minutes.

Returns:

True if it is ready for use, False if not.

imu.stationary() bool

Checks if the device is currently stationary (not moving).

Returns:

True if stationary for at least a second, False if it is moving.

imu.up() Side

Checks which side of the hub currently faces upward.

Returns:

Side.TOP, Side.BOTTOM, Side.LEFT, Side.RIGHT, Side.FRONT or Side.BACK.

../_images/pybricks_blockTilt_EssentialHub_imu.tilt.pitch.svg

../_images/pybricks_blockTilt_EssentialHub_imu.tilt.roll.svg

imu.tilt() Tuple[int, int]

Gets the pitch and roll angles. This is relative to the user-specified neutral orientation.

The order of rotation is pitch-then-roll. This is equivalent to a positive rotation along the robot y-axis and then a positive rotation along the x-axis.

Returns:

Tuple of pitch and roll angles in degrees.

../_images/pybricks_blockImuAcceleration_EssentialHub.svg

imu.acceleration(axis) float: mm/s²
imu.acceleration() vector: mm/s²

Gets the acceleration of the device along a given axis in the robot reference frame.

Parameters:

axis (Axis) – Axis along which the acceleration should be measured.

Returns:

Acceleration along the specified axis. If you specify no axis, this returns a vector of accelerations along all axes.

../_images/pybricks_blockImuRotation_EssentialHub_imu.angular_velocity.svg

imu.angular_velocity(axis) float: deg/s
imu.angular_velocity() vector: deg/s

Gets the angular velocity of the device along a given axis in the robot reference frame.

Parameters:

axis (Axis) – Axis along which the angular velocity should be measured.

Returns:

Angular velocity along the specified axis. If you specify no axis, this returns a vector of accelerations along all axes.

../_images/pybricks_blockImuGetHeading_EssentialHub.svg

imu.heading() float: deg

Gets the heading angle of your robot. A positive value means a clockwise turn.

The heading is 0 when your program starts. The value continues to grow even as the robot turns more than 180 degrees. It does not wrap around to -180 like it does in some apps.

Note

For now, this method only keeps track of the heading while the robot is on a flat surface.

This means that the value is no longer correct if you lift it from the table. To solve this, you can call reset_heading to reset the heading to a known value after you put it back down. For example, you could align your robot with the side of the competition table and reset the heading 90 degrees as the new starting point.

Returns:

Heading angle relative to starting orientation.

../_images/pybricks_blockImuResetHeading_EssentialHub.svg

imu.reset_heading(angle)

Resets the accumulated heading angle of the robot.

Parameters:

angle (Number, deg) – Value to which the heading should be reset.

../_images/pybricks_blockImuRotation_EssentialHub_imu.rotation.svg

imu.rotation(axis) float: deg

Gets the rotation of the device along a given axis in the robot reference frame.

This value is useful if your robot only rotates along the requested axis. For general three-dimensional motion, use the orientation() method instead.

The value starts counting from 0 when you initialize this class.

Parameters:

axis (Axis) – Axis along which the rotation should be measured.

Returns:

The rotation angle.

imu.orientation() Matrix

Gets the three-dimensional orientation of the robot in the robot reference frame.

It returns a rotation matrix whose columns represent the X, Y, and Z axis of the robot.

Note

This method is not yet implemented.

Returns:

The rotation matrix.

imu.settings(angular_velocity_threshold, acceleration_threshold)
imu.settings() Tuple[float, float]

Configures the IMU settings. If no arguments are given, this returns the current values.

The angular_velocity_threshold and acceleration_threshold define when the hub is considered stationary. If all measurements stay below these thresholds for one second, the IMU will recalibrate itself.

In a noisy room with high ambient vibrations (such as a competition hall), it is recommended to increase the thresholds slightly to give your robot the chance to calibrate. To verify that your settings are working as expected, test that the stationary() method gives False if your robot is moving, and True if it is sitting still for at least a second.

Parameters:
  • angular_velocity_threshold (Number, deg/s) – The threshold for angular velocity. The default value is 1.5 deg/s.

  • acceleration_threshold (Number, mm/s²) – The threshold for angular velocity. The default value is 250 mm/s².

Using connectionless Bluetooth messaging

../_images/pybricks_blockBleBroadcast_EssentialHub.svg

ble.broadcast(data)

Starts broadcasting the given data on the broadcast_channel you selected when initializing the hub.

Data may be of type int, float, str, bytes, True, or False, or a list thereof.

Choose None to stop broadcasting. This helps improve performance when you don’t need the broadcast feature, especially when observing at the same time.

The total data size is quite limited (26 bytes). True and False take 1 byte each. float takes 5 bytes. int takes 2 to 5 bytes depending on how big the number is. str and bytes take the number of bytes in the object plus one extra byte.

When multitasking, only one task can broadcast at a time. To broadcast information from multiple tasks (or block stacks), you could use a dedicated separate task that broadcast new values when one or more variables change.

Parameters:

data – The value or values to be broadcast.

New in version 3.3.

../_images/pybricks_blockBleObserve_EssentialHub.svg

ble.observe(channel) bool | int | float | str | bytes | tuple | None

Retrieves the last observed data for a given channel.

Receiving data is more reliable when the hub is not connected to a computer or other devices at the same time.

Parameters:

channel (int) – The channel to observe (0 to 255).

Returns:

The received data in the same format as it was sent, or None if no recent data is available.

New in version 3.3.

ble.signal_strength(channel) int: dBm

Gets the average signal strength in dBm for the given channel.

This indicates how near the broadcasting device is. Nearby devices may have a signal strength around -40 dBm, while far away devices might have a signal strength around -70 dBm.

Parameters:

channel (int) – The channel number (0 to 255).

Returns:

The signal strength or -128 if there is no recent observed data.

New in version 3.3.

ble.version() str

Gets the firmware version from the Bluetooth chip.

New in version 3.3.

Using the battery

../_images/pybricks_blockBatteryMeasure_EssentialHub_battery.voltage.svg

battery.voltage() int: mV

Gets the voltage of the battery.

Returns:

Battery voltage.

../_images/pybricks_blockBatteryMeasure_EssentialHub_battery.current.svg

battery.current() int: mA

Gets the current supplied by the battery.

Returns:

Battery current.

Getting the charger status

charger.connected() bool

Checks whether a charger is connected via USB.

Returns:

True if a charger is connected, False if not.

charger.current() int: mA

Gets the charging current.

Returns:

Charging current.

charger.status() int

Gets the status of the battery charger, represented by one of the following values. This corresponds to the battery light indicator right next to the USB port.

  1. Not charging (light is off).

  2. Charging (light is red).

  3. Charging is complete (light is green).

  4. There is a problem with the charger (light is yellow).

Returns:

Status value.

System control

system.name() str

Gets the hub name. This is the name you see when connecting via Bluetooth.

Returns:

The hub name.

system.storage(offset, write=)
system.storage(offset, read=) bytes

Reads or writes binary data to persistent storage.

This lets you store data that can be used the next time you run the program.

The data will be saved to flash memory when you turn the hub off normally. It will not be saved if the batteries are removed while the hub is still running.

Once saved, the data will remain available even after you remove the batteries.

Parameters:
  • offset (int) – The offset from the start of the user storage memory, in bytes.

  • read (int) – The number of bytes to read. Omit this argument when writing.

  • write (bytes) – The bytes to write. Omit this argument when reading.

Returns:

The bytes read if reading, otherwise None.

Raises:

ValueError – If you try to read or write data outside of the allowed range.

You can store up to 512 bytes of data on this hub.

system.shutdown()

Stops your program and shuts the hub down.

system.reset_reason() int

Finds out how and why the hub (re)booted. This can be useful to diagnose some problems.

Returns:

  • 0 if the hub was previously powered off normally.

  • 1 if the hub rebooted automatically, like after a firmware update.

  • 2 if the hub previously crashed due to a watchdog timeout, which indicates a firmware issue.

Status light examples

Turning the light on and off

from pybricks.hubs import EssentialHub
from pybricks.parameters import Color
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

# Turn the light on and off 5 times.
for i in range(5):

    hub.light.on(Color.RED)
    wait(1000)

    hub.light.off()
    wait(500)

Changing brightness and using custom colors

from pybricks.hubs import EssentialHub
from pybricks.parameters import Color
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

# Show the color at 30% brightness.
hub.light.on(Color.RED * 0.3)

wait(2000)

# Use your own custom color.
hub.light.on(Color(h=30, s=100, v=50))

wait(2000)

# Go through all the colors.
for hue in range(360):
    hub.light.on(Color(hue))
    wait(10)

Creating light animations

from pybricks.hubs import EssentialHub
from pybricks.parameters import Color
from pybricks.tools import wait
from umath import sin, pi

# Initialize the hub.
hub = EssentialHub()

# Make an animation with multiple colors.
hub.light.animate([Color.RED, Color.GREEN, Color.NONE], interval=500)

wait(10000)

# Make the color RED grow faint and bright using a sine pattern.
hub.light.animate([Color.RED * (0.5 * sin(i / 15 * pi) + 0.5) for i in range(30)], 40)

wait(10000)

# Cycle through a rainbow of colors.
hub.light.animate([Color(h=i * 8) for i in range(45)], interval=40)

wait(10000)

IMU examples

Testing which way is up

from pybricks.hubs import EssentialHub
from pybricks.parameters import Color, Side
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

# Define colors for each side in a dictionary.
SIDE_COLORS = {
    Side.TOP: Color.RED,
    Side.BOTTOM: Color.BLUE,
    Side.LEFT: Color.GREEN,
    Side.RIGHT: Color.YELLOW,
    Side.FRONT: Color.MAGENTA,
    Side.BACK: Color.BLACK,
}

# Keep updating the color based on detected up side.
while True:

    # Check which side of the hub is up.
    up_side = hub.imu.up()

    # Change the color based on the side.
    hub.light.on(SIDE_COLORS[up_side])

    # Also print the result.
    print(up_side)
    wait(50)

Reading the tilt value

from pybricks.hubs import EssentialHub
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

while True:
    # Read the tilt values.
    pitch, roll = hub.imu.tilt()

    # Print the result.
    print(pitch, roll)
    wait(200)

Using a custom hub orientation

from pybricks.hubs import EssentialHub
from pybricks.tools import wait
from pybricks.parameters import Axis

# Initialize the hub. In this case, specify that the hub is mounted with the
# top side facing forward and the front side facing to the right.
# For example, this is how the hub is mounted in BLAST in the 51515 set.
hub = EssentialHub(top_side=Axis.X, front_side=-Axis.Y)

while True:
    # Read the tilt values. Now, the values are 0 when BLAST stands upright.
    # Leaning forward gives positive pitch. Leaning right gives positive roll.
    pitch, roll = hub.imu.tilt()

    # Print the result.
    print(pitch, roll)
    wait(200)

Reading acceleration and angular velocity vectors

from pybricks.hubs import EssentialHub
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

# Get the acceleration vector in g's.
print(hub.imu.acceleration() / 9810)

# Get the angular velocity vector.
print(hub.imu.angular_velocity())

# Wait so we can see what we printed
wait(5000)

Reading acceleration and angular velocity on one axis

from pybricks.hubs import EssentialHub
from pybricks.tools import wait
from pybricks.parameters import Axis

# Initialize the hub.
hub = EssentialHub()

# Get the acceleration or angular_velocity along a single axis.
# If you need only one value, this is more memory efficient.
while True:

    # Read the forward acceleration.
    forward_acceleration = hub.imu.acceleration(Axis.X)

    # Read the yaw rate.
    yaw_rate = hub.imu.angular_velocity(Axis.Z)

    # Print the yaw rate.
    print(yaw_rate)
    wait(100)

Bluetooth examples

Broadcasting data to other hubs

from pybricks.hubs import EssentialHub
from pybricks.pupdevices import Motor
from pybricks.parameters import Port
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub(broadcast_channel=1)

# Initialize the motors.
left_motor = Motor(Port.A)
right_motor = Motor(Port.B)

while True:
    # Read the motor angles to be sent to the other hub.
    left_angle = left_motor.angle()
    right_angle = right_motor.angle()

    # Set the broadcast data and start broadcasting if not already doing so.
    data = (left_angle, right_angle)
    hub.ble.broadcast(data)

    # Broadcasts are only sent every 100 milliseconds, so there is no reason
    # to call the broadcast() method more often than that.
    wait(100)

Observing data from other hubs

from pybricks.hubs import EssentialHub
from pybricks.pupdevices import Motor
from pybricks.parameters import Color, Port
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub(observe_channels=[1])

# Initialize the motors.
left_motor = Motor(Port.A)
right_motor = Motor(Port.B)

while True:
    # Receive broadcast from the other hub.

    data = hub.ble.observe(1)

    if data is None:
        # No data has been received in the last 1 second.
        hub.light.on(Color.RED)
    else:
        # Data was received and is less that one second old.
        hub.light.on(Color.GREEN)

        # *data* contains the same values in the same order
        # that were passed to hub.ble.broadcast() on the
        # other hub.
        left_angle, right_angle = data

        # Make the motors on this hub mirror the position of the
        # motors on the other hub.
        left_motor.track_target(left_angle)
        right_motor.track_target(right_angle)

    # Broadcasts are only sent every 100 milliseconds, so there is
    # no reason to call the observe() method more often than that.
    wait(100)

System examples

Using the stop button during your program

from pybricks.hubs import EssentialHub
from pybricks.parameters import Color, Button
from pybricks.tools import wait, StopWatch

# Initialize the hub.
hub = EssentialHub()

# Disable the stop button.
hub.system.set_stop_button(None)

# Check the button for 5 seconds.
watch = StopWatch()
while watch.time() < 5000:

    # Set light to green if pressed, else red.
    if hub.buttons.pressed():
        hub.light.on(Color.GREEN)
    else:
        hub.light.on(Color.RED)

# Enable the stop button again.
hub.system.set_stop_button(Button.CENTER)

# Now you can press the stop button as usual.
wait(5000)

Turning the hub off

from pybricks.hubs import EssentialHub
from pybricks.tools import wait

# Initialize the hub.
hub = EssentialHub()

# Say goodbye and give some time to send it.
print("Goodbye!")
wait(100)

# Shut the hub down.
hub.system.shutdown()