Python library to interact with Move Hub

Move Hub is central robotic controller block of LEGO Boost Set.

Best way to start with this library is to look into demo.py file, and run it.

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

Features

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

Usage

Install library like this:

pip install https://github.com/undera/pylgbst/archive/0.2.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)

TODO: more usage instructions

General Information

connection params hub's devices detect process & fields to access them general subscription modes & granularity info good practice is to unsubscribe, especially when used with DebugServer

Only one, very last subscribe mode is in effect, with many subscriber callbacks allowed.

Motors

Motor Rotation Sensors

Tilt Sensor

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

Color & Distance Sensor

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

LED

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.

Push Button

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)

Power Voltage & Battery

MoveHub class has field battery to subscribe to battery voltage status. Callback accepts single parameter with current value. The range of values is unknown, it's 2-byte integer. Every time data is received, value is also written into last_value field of Battery object.

from pylgbst import MoveHub
import time

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

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

Debug Server

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.

TODO

• Give nice documentation examples, don't forget to mention logging
• document all API methods
• make sure unit tests cover all important code
• handle device detach and device attach events on ports C/D
• generalize getting device info + give constants (low priority)
• organize requesting and printing device info on startup - firmware version at least
• make debug server to re-establish BLE connection on loss

Links

• 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