ev3-dc 0.9.9

EV3 direct commands

Use python3 to program your LEGO Mindstorms EV3. The program runs on the local host and sends direct commands to the EV3 device. It communicates via Bluetooth, WiFi or USB. There is no need to boot the EV3 device from an SD Card or manipulate its software. You can use it as it is, the EV3 is designed to execute commands which come from outside. If you prefer coding from scratch, read this blog, if you like to benefit from preliminary work, then use module ev3_dc.

Installation

python3 -m pip install --user ev3_dc

Examples

Writing and sending direct commands

The following program communicates via USB with an EV3 device and plays a tone with a frequency of 440 Hz for a duration of 1 sec. This says, you need to connect the EV3 device and your computer with an USB cable.

import ev3_dc as ev3

my_ev3 = ev3.EV3(protocol=ev3.USB)
my_ev3.verbosity = 1
ops = b''.join((
    ev3.opSound,
    ev3.TONE,
    ev3.LCX(1),  # VOLUME
    ev3.LCX(440),  # FREQUENCY
    ev3.LCX(1000),  # DURATION
))
my_ev3.send_direct_cmd(ops)

The output shows the request, which was sent to the EV3 device and the corresponding response:

13:02:23.425843 Sent 0x|0E:00|2A:00|00|00:00|94:01:01:82:B8:01:82:E8:03|
13:02:23.432733 Recv 0x|03:00|2A:00|02|

Subclasses of EV3 with specialized APIs

Method play_tone of class Jukebox also plays tones:

import ev3_dc as ev3

jukebox = ev3.Jukebox(protocol=ev3.BLUETOOTH, host='00:16:53:42:2B:99')
jukebox.verbosity = 1
jukebox.play_tone("a'", duration=1)

This program does the very same thing via Bluetooth! Before you can run it, you need to pair the two devices (the computer, that executes the program and the EV3 device) and replace the MAC-address 00:16:53:42:2B:99 by the one of your EV3. The output:

13:05:11.324701 Sent 0x|0E:00|2A:00|80|00:00|94:01:01:82:B8:01:82:E8:03|

Some remarks:

• Protocol USB replies all requests to provide collisions. Protocol BLUETOOTH is much slower and replies only requests, which demand it.

• Module ev3_dc provides objects with specialized functionality. Behind the scene, this functionality depends on messages, which are sent to the EV3 device and replied by the EV3 device.

Independent Tasks

Specialized classes (e.g. class Jukebox) provide factory methods, which return thread_task.Task objects. Thread tasks allow to start, stop and continue independent tasks.

import ev3_dc as ev3

jukebox = ev3.Jukebox(protocol=ev3.WIFI)
antemn = jukebox.song(ev3.EU_ANTEMN)

antemn.start()

This program plays the EU antemn. Before you can execute it, you need to connect both devices (the computer, that runs the program and the EV3 device) with the same LAN (local area network), the EV3 device must be connected via WiFi. If you don’t own a WiFi dongle, modify the protocol and select ev3.BLUETOOTH or ev3.USB.

Some remarks:

• Method song() returns a thread_task.Task object and we need to start it explicitly. It plays tones and changes the LED-colors.

• Starting a thread task does not block the program nor does it block the EV3 device. It runs in the background and allows to do additional things parallel.

• Alternatively, you can start a thread task without mutlithreading by antemn.start(thread=False). This lets it behave like any normal callable.

Specialized Subclasses handle Sensors and Motors

Specialized subclasses of class EV3, like Touch, Infrared, Ultrasonic, Color, Motor, TwoWheelVehicle, Sound or Voice handle sensors, motors, sound or text to speech. You can use multiple of these objects parallel and all them can share a single physical EV3 device. You can also build complex robots with more than one EV3 device and control these robots easily by a single python program.

import ev3_dc as ev3

with ev3.Touch(ev3.PORT_1, protocol=ev3.USB) as touch_1:
    touch_4 = ev3.Touch(ev3.PORT_4, ev3_obj=touch_1)
    voice = ev3.Voice(ev3_obj=touch_1, volume=100)

    touched_1 = touch_1.touched
    touched_4 = touch_4.touched
    if touched_1 and touched_4:
        txt = 'both sensors are touched'
    elif touched_1:
        txt = 'only sensor 1 is touched'
    elif touched_4:
        txt = 'only sensor 4 is touched'
    else:
        txt = 'none of the sensors is touched'

    voice.speak(txt).start(thread=False)

Some remarks:

• You need to connect two touch sensors, one at port 1, the other at port 4 and you need to connect your EV3 device and your computer with an USB cable.

• Class EV3 and all its subclasses support the with statement.

• touch_4 and voice use the connection of touch_1. This is done by setting keyword argument ev3_obj=touch_1.

• If you have more than a single EV3 device connected via USB, this program will fail. This special case needs keyword argument host, e.g. ev3.Touch(ev3.PORT_1, protocol=ev3.USB, host='00:16:53:42:2B:99'), to identify the device (for protocol BLUETOOTH keyword argument host is mandatory).

• Method speak() returns a thread_task.Task object, which we start threadless.

• This program depends on the tool ffmpeg and you need to have it installed on your computer.

Read ev3-dc.readthedocs.io for more details.