Move Hub is central controller block of LEGO® Boost Robotics Set.

In fact, Move Hub is just Bluetooth hardware, all manipulations are done with commands passed through Bluetooth Low Energy (BLE) wireless protocol. One of ways to issue these commands is to write Python program using this library.

Best way to start is to look into demo.py file, and run it (assuming you have installed library).

If you have Vernie assembled, you might run scripts from vernie directory.

Demonstrational video:

• auto-detect and connect to Move Hub device
• auto-detects peripheral devices connected to Hub
• constant, angled and timed movement for motors, rotation sensor subscription
• color & distance sensor: several modes to measure distance, color and luminosity
• tilt sensor subscription: 2 axis, 3 axis, bump detect modes
• LED color change
• push button status subscription
• battery voltage subscription available
• permanent Bluetooth connection server for faster debugging

Install library like this:

pip install https://github.com/undera/pylgbst/archive/0.4.tar.gz

Then instantiate MoveHub object and start invoking its methods. Following is example to just print peripherals detected on Hub:

from pylgbst import MoveHub

hub = MoveHub()

for device in hub.devices:
    print(device)

MoveHub provides motors via following fields:

• motor_A - port A
• motor_B - port B
• motor_AB - motor group of A+B manipulated together
• motor_external - external motor attached to port C or D

Methods to activate motors are:

• constant(speed_primary, speed_secondary) - enables motor with specified speed forever
• timed(time, speed_primary, speed_secondary) - enables motor with specified speed for time seconds, float values accepted
• angled(angle, speed_primary, speed_secondary) - makes motor to rotate to specified angle, angle value is integer degrees, can be negative and can be more than 360 for several rounds
• stop() - stops motor at once, it is equivalent for constant(0)

Parameter speed_secondary is used when it is motor group of motor_AB running together. By default, speed_secondary equals speed_primary. Speed values range is -1.0 to 1.0, float values.

All these methods are synchronous by default, means method does not return untill it gets confirmation from Hub that command has completed. You can pass async=True parameter to any of methods to switch into asynchronous, which means command will return immediately, without waiting for rotation to complete. Be careful with asynchronous calls, as they make Hub to stop reporting synchronizing statuses.

An example:

from pylgbst import MoveHub
import time

hub = MoveHub()

hub.motor_A.timed(0.5, 0.8)
hub.motor_A.timed(0.5, -0.8)

hub.motor_B.angled(90, 0.8)
hub.motor_B.angled(-90, 0.8)

hub.motor_AB.timed(1.5, 0.8, -0.8)
hub.motor_AB.angled(90, 0.8, -0.8)

hub.motor_external.constant(0.2)
time.sleep(2)
hub.motor_external.stop()

Any motor allows to subscribe to its rotation sensor. Two sensor modes are available: rotation angle (EncodedMotor.SENSOR_ANGLE) and rotation speed (EncodedMotor.SENSOR_SPEED). Example:

from pylgbst import MoveHub, EncodedMotor
import time

def callback(angle):
    print("Angle: %s" % angle)

hub = MoveHub()

hub.motor_A.subscribe(callback, mode=EncodedMotor.SENSOR_ANGLE)
time.sleep(60) # rotate motor A
hub.motor_A.unsubscribe(callback)

MoveHub's internal tilt sensor is available through tilt_sensor field. There are several modes to subscribe to sensor, providing 2-axis, 3-axis and bump detect data.

An example:

from pylgbst import MoveHub, TiltSensor
import time

def callback(pitch, roll, yaw):
    print("Pitch: %s / Roll: %s / Yaw: %s" % (pitch, roll, yaw))

hub = MoveHub()

hub.tilt_sensor.subscribe(callback, mode=TiltSensor.MODE_3AXIS_FULL)
time.sleep(60) # turn MoveHub block in different ways
hub.tilt_sensor.unsubscribe(callback)

TiltSensor sensor mode constants:

• MODE_2AXIS_SIMPLE - use callback(state) for 2-axis simple state detect
• MODE_2AXIS_FULL - use callback(roll, pitch) for 2-axis roll&pitch degree values
• MODE_3AXIS_SIMPLE - use callback(state) for 3-axis simple state detect
• MODE_3AXIS_FULL - use callback(roll, pitch) for 2-axis roll&pitch degree values
• MODE_BUMP_COUNT - use callback(count) to detect bumps

There are tilt sensor constants for "simple" states, for 2-axis mode their names are also available through TiltSensor.DUO_STATES:

• DUO_HORIZ - "HORIZONTAL"
• DUO_DOWN - "DOWN"
• DUO_LEFT - "LEFT"
• DUO_RIGHT - "RIGHT"
• DUO_UP - "UP"

For 3-axis simple mode map name is TiltSensor.TRI_STATES with values:

• TRI_BACK - "BACK"
• TRI_UP - "UP"
• TRI_DOWN - "DOWN"
• TRI_LEFT - "LEFT"
• TRI_RIGHT - "RIGHT"
• TRI_FRONT - "FRONT"

Field named color_distance_sensor holds instance of ColorDistanceSensor, if one is attached to MoveHub. Sensor has number of different modes to subscribe.

Colors that are detected are part of COLORS map (see LED section). Only several colors are possible to detect: BLACK, BLUE, CYAN, YELLOW, RED, WHITE. Sensor does its best to detect best color, but only works when sample is very close to sensor.

Distance works in range of 0-10 inches, with ability to measure last inch in higher detail.

Simple example of subscribing to sensor:

from pylgbst import MoveHub, ColorDistanceSensor
import time

def callback(clr, distance):
    print("Color: %s / Distance: %s" % (clr, distance))

hub = MoveHub()

hub.color_distance_sensor.subscribe(callback, mode=ColorDistanceSensor.COLOR_DISTANCE_FLOAT)
time.sleep(60) # play with sensor while it waits   
hub.color_distance_sensor.unsubscribe(callback)

Subscription mode constants in class ColorDistanceSensor are:

• COLOR_DISTANCE_FLOAT - default mode, use callback(color, distance) where distance is float value in inches
• COLOR_ONLY - use callback(color)
• DISTANCE_INCHES - use callback(color) measures distance in integer inches count
• COUNT_2INCH - use callback(count) - it counts crossing distance ~2 inches in front of sensor
• DISTANCE_HOW_CLOSE - use callback(value) - value of 0 to 255 for 30 inches, larger with closer distance
• DISTANCE_SUBINCH_HOW_CLOSE - use callback(value) - value of 0 to 255 for 1 inch, larger with closer distance
• LUMINOSITY - use callback(luminosity) where luminosity is float value from 0 to 1
• OFF1 and OFF2 - seems to turn sensor LED and notifications off
• STREAM_3_VALUES - use callback(val1, val2, val3), sends some values correlating to distance, not well understood at the moment

Tip: laser pointer pointing to sensor makes it to trigger distance sensor

MoveHub class has field led to access color LED near push button. To change its color, use set_color(color) method.

You can obtain colors are present as constants COLOR_* and also a map of available color-to-name as COLORS. There are 12 color values, including COLOR_BLACK and COLOR_NONE which turn LED off.

Additionally, you can subscribe to LED color change events, using callback function as shown in example below.

from pylgbst import MoveHub, COLORS, COLOR_NONE, COLOR_RED
import time

def callback(clr):
    print("Color has changed: %s" % clr)

hub = MoveHub()
hub.led.subscribe(callback)

hub.led.set_color(COLOR_RED)
for color in COLORS:
    hub.led.set_color(color)
    time.sleep(0.5)
    
hub.led.set_color(COLOR_NONE)
hub.led.unsubscribe(callback)

Tip: blinking orange color of LED means battery is low.

MoveHub class has field button to subscribe to button press and release events.

Note that Button class is not real Peripheral, as it has no port and not listed in devices field of Hub. Still, subscribing to button is done usual way:

from pylgbst import MoveHub

def callback(is_pressed):
    print("Btn pressed: %s" % is_pressed)

hub = MoveHub()
hub.button.subscribe(callback)

MoveHub class has field voltage to subscribe to battery voltage status. Callback accepts single parameter with current value. The range of values is float between 0 and 1.0. Every time data is received, value is also written into last_value field of Voltage object. Values less than 0.2 are known as lowest values, when unit turns off.

from pylgbst import MoveHub
import time

def callback(value):
    print("Voltage: %s" % value)

hub = MoveHub()
hub.voltage.subscribe(callback)
time.sleep(1)
print ("Value: " % hub.voltage.last_value)

There is optional parameter for MoveHub class constructor, accepting instance of Connection object. By default, it uses instance of BLEConnection to connect directly to Move Hub. You can specify instance of DebugServerConnection if you are using Debug Server (more details below).

If you want to specify name for Bluetooth interface to use on local computer, create instance of BLEConnection and call connect(if_name) method of connection. Then pass it to MoveHub constructor. Like this:

from pylgbst import BLEConnection, MoveHub

conn = BLEConnection()
conn.connect("hci1")

hub = MoveHub(conn)

As part of instantiating process, MoveHub waits up to 1 minute for all builtin devices to appear, such as motors on ports A and B, tilt sensor, button and battery. This not guarantees that external motor and/or color sensor will be present right after MoveHub instantiated. Usually, sleeping for couple of seconds gives it enough time to detect everything.

Each sensor usually has several different "subscription modes", differing with callback parameters and value semantics.

There is optional granularity parameter for each subscription call, by default it is 1. This parameter tells Hub when to issue sensor data notification. Value of notification has to change greater or equals to granularity to issue notification. This means that specifying 0 will cause it to constantly send notifications, and specifying 5 will cause less frequent notifications, only when values change for more than 5 (inclusive).

It is possible to subscribe with multiple times for the same sensor. Only one, very last subscribe mode is in effect, with many subscriber callbacks allowed to receive notifications.

Good practice for any program is to unsubscribe from all sensor subscriptions before ending, especially when used with DebugServer.

Running debug server opens permanent BLE connection to Hub and listening on TCP port for communications. This avoids the need to re-start Hub all the time.

There is DebugServerConnection class that you can use with it, instead of BLEConnection.

Starting debug server is done like this:

sudo python -c "from pylgbst.comms import *; \
    import logging; logging.basicConfig(level=logging.DEBUG); \
    DebugServer(BLEConnection().connect()).start()"

Then push green button on MoveHub, so permanent BLE connection will be established.

• document all API methods
• make sure unit tests cover all important code
• make debug server to re-establish BLE connection on loss

• https://github.com/JorgePe/BOOSTreveng - source of protocol knowledge
• https://github.com/spezifisch/sphero-python/blob/master/BB8joyDrive.py - example with another approach to bluetooth libs

Some things around visual programming:

• https://github.com/RealTimeWeb/blockpy
• https://ru.wikipedia.org/wiki/App_Inventor
• https://en.wikipedia.org/wiki/Blockly