ping li
Created December 30, 2019

Smart LEGO Train

We can play with a remote controlled LEGO train, but we thought we could use it with EV3 and Alexa. We also added motors to control it.

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Things used in this project


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Communication Structure


Running on EV3

#!/usr/bin/env python3

import os
import sys
import time
import logging
import json
import random
import threading

from enum import Enum
from agt import AlexaGadget

from ev3dev2.led import Leds
from ev3dev2.sound import Sound
from ev3dev2.motor import OUTPUT_A, OUTPUT_B, SpeedPercent, MediumMotor

# Set the logging level to INFO to see messages from AlexaGadget
logging.basicConfig(level=logging.INFO, stream=sys.stdout, format='%(message)s')
logger = logging.getLogger(__name__)

class Command(Enum):
    The list of preset commands and their invocation variation.
    These variations correspond to the skill slot values.
    FASTER = ['faster','fast','speed up','start']
    SLOWER = ['slower','slow','slow down']
    BRAKE = ['brake','stop']

class MindstormsGadget(AlexaGadget):
    A Mindstorms gadget that performs movement based on voice commands.
    Two types of commands are supported.

    def __init__(self):
        Performs Alexa Gadget initialization routines and ev3dev resource allocation.

        # Gadget state
        self.patrol_mode = False

        # Ev3dev initialization
        self.leds = Leds()
        self.sound = Sound()
        self.speedDrive = MediumMotor(OUTPUT_A)
        self.breekDrive = MediumMotor(OUTPUT_B)

    def on_connected(self, device_addr):
        Gadget connected to the paired Echo device.
        :param device_addr: the address of the device we connected to
        self.leds.set_color("LEFT", "GREEN")
        self.leds.set_color("RIGHT", "GREEN")"{} connected to Echo device".format(self.friendly_name))

    def on_disconnected(self, device_addr):
        Gadget disconnected from the paired Echo device.
        :param device_addr: the address of the device we disconnected from
        self.leds.set_color("LEFT", "BLACK")
        self.leds.set_color("RIGHT", "BLACK")"{} disconnected from Echo device".format(self.friendly_name))

    def on_custom_mindstorms_gadget_control(self, directive):
        Handles the Custom.Mindstorms.Gadget control directive.
        :param directive: the custom directive with the matching namespace and name
            payload = json.loads(directive.payload.decode("utf-8"))
            print("Control payload: {}".format(payload), file=sys.stderr)
            control_type = payload["type"]
            if control_type == "move":

                # Expected params: [direction]
                self._move(payload["direction"], int(payload["duration"]), int(payload["speed"]))

        except KeyError:
            print("Missing expected parameters: {}".format(directive), file=sys.stderr)

    def _move(self, direction, duration: int, speed: int, is_blocking=False):
        Handles move commands from the directive.
        Right and left movement can under or over turn depending on the surface type.
        :param direction: the move direction
        :param duration: the duration in seconds
        :param speed: the speed percentage as an integer
        :param is_blocking: if set, motor run until duration expired before accepting another command

        if direction in Command.FASTER.value:
            print("Move command: ({})".format(direction), file=sys.stderr)
            self.speedDrive.on_for_rotations(SpeedPercent(20), 0.05)

        if direction in Command.SLOWER.value:
            print("Move command: ({})".format(direction), file=sys.stderr)
            self.speedDrive.on_for_rotations(SpeedPercent(-20), 0.05)

        if direction in Command.BRAKE.value:
            print("Move command: ({})".format(direction), file=sys.stderr)
            self.breekDrive.on_for_rotations(SpeedPercent(30), 0.3)
            self.breekDrive.on_for_rotations(SpeedPercent(-30), 0.3)

if __name__ == '__main__':

    gadget = MindstormsGadget()

    # Set LCD font and turn off blinking LEDs
    os.system('setfont Lat7-Terminus12x6')
    gadget.leds.set_color("LEFT", "BLACK")
    gadget.leds.set_color("RIGHT", "BLACK")

    # Startup sequence
    gadget.sound.play_song((('C4', 'e'), ('D4', 'e'), ('E5', 'q')))
    gadget.leds.set_color("LEFT", "GREEN")
    gadget.leds.set_color("RIGHT", "GREEN")

    # Gadget main entry point

    # Shutdown sequence
    gadget.sound.play_song((('E5', 'e'), ('C4', 'e')))
    gadget.leds.set_color("LEFT", "BLACK")
    gadget.leds.set_color("RIGHT", "BLACK")

AWS Lambda

const Alexa = require('ask-sdk-core');
const Util = require('./util');
const Common = require('./common');

// The namespace of the custom directive to be sent by this skill
const NAMESPACE = 'Custom.Mindstorms.Gadget';

// The name of the custom directive to be sent this skill
const NAME_CONTROL = 'control';

const LaunchRequestHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'LaunchRequest';
    handle: async function(handlerInput) {

        let request = handlerInput.requestEnvelope;
        let { apiEndpoint, apiAccessToken } = request.context.System;
        let apiResponse = await Util.getConnectedEndpoints(apiEndpoint, apiAccessToken);
        if ((apiResponse.endpoints || []).length === 0) {
            return handlerInput.responseBuilder
            .speak(`I couldn't find an EV3 Brick connected to this Echo device. Please check to make sure your EV3 Brick is connected, and try again.`)

        // Store the gadget endpointId to be used in this skill session
        let endpointId = apiResponse.endpoints[0].endpointId || [];
        Util.putSessionAttribute(handlerInput, 'endpointId', endpointId);

        return handlerInput.responseBuilder
            .speak("Welcome, you can start issuing move commands")
            .reprompt("Awaiting commands")

// Add the speed value to the session attribute.
// This allows other intent handler to use the specified speed value
// without asking the user for input.
const SetSpeedIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'SetSpeedIntent';
    handle: function (handlerInput) {

        // Bound speed to (1-100)
        let speed = Alexa.getSlotValue(handlerInput.requestEnvelope, 'Speed');
        speed = Math.max(1, Math.min(100, parseInt(speed)));
        Util.putSessionAttribute(handlerInput, 'speed', speed);

        return handlerInput.responseBuilder
            .speak(`speed set to ${speed} percent.`)
            .reprompt("awaiting command")

// Construct and send a custom directive to the connected gadget with
// data from the MoveIntent request.
const MoveIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'MoveIntent';
    handle: function (handlerInput) {
        const request = handlerInput.requestEnvelope;
        const direction = Alexa.getSlotValue(request, 'Direction');

        // Duration is optional, use default if not available
        const duration = Alexa.getSlotValue(request, 'Duration') || "2";

        // Get data from session attribute
        const attributesManager = handlerInput.attributesManager;
        const speed = attributesManager.getSessionAttributes().speed || "50";
        const endpointId = attributesManager.getSessionAttributes().endpointId || [];

        // Construct the directive with the payload containing the move parameters
        const directive =, NAMESPACE, NAME_CONTROL,
                type: 'move',
                direction: direction,
                duration: duration,
                speed: speed

        const speechOutput = (direction === "brake")
            ?  "Applying brake"
            : `${direction} ${duration} seconds at ${speed} percent speed`;

        return handlerInput.responseBuilder
            .reprompt("awaiting command")

// Construct and send a custom directive to the connected gadget with data from
// the SetCommandIntent request.
const SetCommandIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'SetCommandIntent';
    handle: function (handlerInput) {

        let command = Alexa.getSlotValue(handlerInput.requestEnvelope, 'Command');
        if (!command) {
            return handlerInput.responseBuilder
                .speak("Can you repeat that?")
                .reprompt("What was that again?").getResponse();

        const attributesManager = handlerInput.attributesManager;
        let endpointId = attributesManager.getSessionAttributes().endpointId || [];
        let speed = attributesManager.getSessionAttributes().speed || "50";

        // Construct the directive with the payload containing the move parameters
        let directive =, NAMESPACE, NAME_CONTROL,
                type: 'command',
                command: command,
                speed: speed

        return handlerInput.responseBuilder
            .speak(`command ${command} activated`)
            .reprompt("awaiting command")

// The SkillBuilder acts as the entry point for your skill, routing all request and response
// payloads to the handlers above. Make sure any new handlers or interceptors you've
// defined are included below. The order matters - they're processed top to bottom.
exports.handler = Alexa.SkillBuilders.custom()
        Common.IntentReflectorHandler, // make sure IntentReflectorHandler is last so it doesn't override your custom intent handlers


ping li

ping li

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