如何用Python控制LEGO Wedo 2.0的电机

乐高官方提供的编程工具都是图形化的，这篇文章分享下如何用Python来链接控制LEGO Wedo 2.0中提供的蓝牙主控设备和电机。

学习资源

网上有两篇颇有用的文章：

• Controlling a WeDo 2.0 motor
• WeDo 2.0 – reverse engineering

使用pygattlib能够经过Python和蓝牙低功耗设备通信。这个库只支持Linux。

命令行工具和开发环境

经过测试发现，Windows的Linux子系统和VMWare虚拟机是不支持的。我最终选了树莓派作开发环境。 使用系统自带的命令行工具能够直接测试蓝牙链接。 扫描设备获取地址：

sudo hcitool -i hci0 lescan
LE Scan ...
98:07:2D:DD:98:56 (unknown)
98:07:2D:DD:98:56 LPF2 Smart Hub

链接设备：

gatttool -I
[                 ][LE]> connect <ble address>

使用Python建立界面控制程序

安装依赖库以及gattlib:

sudo apt-get update
sudo apt-get install libbluetooth-dev bluez bluez-hcidump libboost-python-dev libboost-thread-dev libglib2.0-dev
sudo pip install gattlib

用Tkinter建立界面：

import Tkinter as tk
from gattlib import DiscoveryService
from gattlib import GATTRequester
from time import sleep
 
def run():
    global button_run
    button_run.after(DELAY, motor_run)
 
def stop():
    global button_stop
    button_stop.after(DELAY, motor_stop)
 
def connect():
    global button_disconnect
    button_disconnect.after(DELAY, smart_hub_connect)
 
def disconnect():
    global button_disconnect
    button_disconnect.after(DELAY, smart_hub_disconnect)
 
def up():
    global button_up
    button_up.after(DELAY, motor_up)
 
def down():
    global button_down
    button_down.after(DELAY, motor_down)
 
 
root = tk.Tk()
root.title("Lego Wedo 2.0 Motor Control")
 
label = tk.Label(root, fg="dark green", text='N/A')
label.pack()
 
button_connect = tk.Button(root, text='Connect Smart Hub', width=BUTTON_WIDTH, command=connect)
button_connect.pack()
 
button_disconnect = tk.Button(root, text='Disconnect Smart Hub', width=BUTTON_WIDTH, command=disconnect, state='disabled')
button_disconnect.pack()
 
button_run = tk.Button(root, text='Run motor', width=BUTTON_WIDTH, command=run, state='disabled')
button_run.pack()
 
button_up = tk.Button(root, text='Speed up', width=BUTTON_WIDTH, command=up, state='disabled')
button_up.pack()
 
button_down = tk.Button(root, text='Speed down', width=BUTTON_WIDTH, command=down, state='disabled')
button_down.pack()
 
button_stop = tk.Button(root, text='Stop motor', width=BUTTON_WIDTH, command=stop, state='disabled')
button_stop.pack()
 
root.mainloop()

使用DiscoveryService和GATTRequester查找链接设备：

def smart_hub_connect():
    service = DiscoveryService("hci0")
    devices = service.discover(2)
 
    for address, name in devices.items():
        if name != '' and 'Smart Hub' in name:
            label['text'] = address
 
            global button_run, button_stop, button_disconnect, req
            button_connect['state'] = 'disabled'
            button_run['state'] = 'normal'
            button_stop['state'] = 'normal'
            button_disconnect['state'] = 'normal'
            button_up['state'] = 'normal'
            button_down['state'] = 'normal'
 
            req = GATTRequester(address, True, "hci0")
            break

运行电机：

def motor_run():
    global req
    if req != None:
        req.write_by_handle(0x3d, str(bytearray([0x01, 0x01, 0x01, 0x64]))
)

第一个字节表明端口号。主控设备上有两个端口，选择对应的端口号。

经过gatttool也能够查看端口变化：

[98:07:2D:DD:98:56][LE]> char-read-hnd 0015                                                                     
Characteristic value/descriptor: 01 01 00 01 01 00 00 00 01 00 00 00                                                    
[98:07:2D:DD:98:56][LE]> char-read-hnd 0015                                                                             
Characteristic value/descriptor: 02 01 01 01 01 00 00 00 01 00 00 00

最后一个字节表明速度。能够经过代码动态调节：

MAX_SPEED = 100
MIN_SPEED = 1
SPEED_CHANGE = 4
 
current_speed = 100
req = None
 
def motor_up():
    global req, current_speed
    if req != None:
        if current_speed == MAX_SPEED:
            return
 
        current_speed += SPEED_CHANGE
        req.write_by_handle(HANDLE, str(bytearray([0x01, 0x01, 0x01, current_speed])))
        sleep(WEDO_DELAY)
 
def motor_down():
    global req, current_speed
    if req != None:
        if current_speed == MIN_SPEED:
            return
 
        current_speed -= SPEED_CHANGE
        req.write_by_handle(HANDLE, str(bytearray([0x01, 0x01, 0x01, current_speed])))
        sleep(WEDO_DELAY)

运行程序的时候，若是没有root权限，会出现错误。

运行界面程序须要用gksudo而不是sudo。

在Windows中能够经过SmarTTY来显示远程的GUI。

源码

https://github.com/yushulx/lego-wedo-motor-control