Trigger brick program from Python

[Fergus O’Callaghan]

Happy New Year! And congratulations on the great website. I have a (hopefully) simple question. I have an EV3 set and I want to trigger a normal Lego Mindstorms program to run on the EV3 brick, from a python script on a PC. Basically this python script runs unattended, and I want it to be able to trigger the EV3 brick to press a physical button.

Communications via either bluetooth or USB would be fine. The question is: do I need a whole SW stack on the PC side to do the communication, or is there perhaps some shortcut I could use directly with the python pybluez module? I can already discover the EV3 using pybluez. But how could I trigger a program to run?

Many thanks,
Fergus

[Anders Søborg]

Although this forum is related to MonoBrick communication here are some Phyton code to send a message to the EV3 from a PC over Bluetooth

import struct
import ctypes
import binascii
import socket
import time
import StringIO
import serial
import struct
from array import array

from serial import * 
from threading import Thread 

class MailboxMessage(): 
    def __init__(self, mailboxName, msg): 
        self.MailboxName = mailboxName
        self.msg = msg
        mailboxNameLength = len(mailboxName)+1
        msgLength = len(msg) +1
        totalLength = mailboxNameLength + msgLength + 7
        self.data = bytearray(b"")
        self.data.append(totalLength)#length
        self.data.append(0)
        self.data.append(100)#sequence number
        self.data.append(0)
        self.data.append(129)#Command type - system command without reply 0x81
        self.data.append(158)#system command type - WriteMailbox 0x9e
        self.data.append(mailboxNameLength)
        self.data = self.data + bytearray(mailboxName)
        self.data.append(0)
        self.data.append(msgLength)
        self.data.append(0)
        self.data = self.data+ bytearray(msg)
        self.data.append(0)
    def Mailbox(self):
        return self.MailboxName
    def Data(self):
        return self.data        
    def Message(self):
        return self.msg

class Receiver(Thread): 
    def __init__(self, serialPort): 
        Thread.__init__(self) 
        self.serialPort = serialPort 
    def run(self): 
        message = []
        messageSize=0
        while True:
            for c in self.serialPort.read(size=1):
                message.append(ord(c))
            if len(message) == 2:
                bytes = array('B', message)
                messageSize = struct.unpack('<H',  bytes )[0]
                #print messageSize
                for c in self.serialPort.read(size=messageSize):
                    message.append(ord(c))
                      
                bytes = array('B', message[6:7])
                mailboxNameLength = struct.unpack('<B',  bytes )[0]
                #bytes = array('B', message[7+mailboxNameLength:7+mailboxNameLength+2])
                #mailboxTextLength = struct.unpack('<H',  bytes )[0]
                mailboxName = array('B', message[7:7+mailboxNameLength-1]).tostring()
                mailboxText = array('B', message[7+mailboxNameLength+2 :messageSize+1]).tostring()
                mailboxMessage = MailboxMessage(mailboxName, mailboxText)
                print mailboxMessage.Mailbox()
                print mailboxMessage.Message()
                message[:] = []
        self.serialPort.close() 

class Sender(Thread): 
    def __init__(self, serialPort): 
        Thread.__init__(self) 
        self.serialPort = serialPort 
    def run(self): 
        text = ""
        print "Enter text to send"
        while(text != "quit\n"): 
            msg = raw_input("")
            mailboxName = "mailbox1"
            self.sendMessage(mailboxName, msg)
        self.serialPort.close()
    def sendMessage(self, mailboxName,msg):
        mailboxMessage = MailboxMessage(mailboxName,msg)
        self.serialPort.write(mailboxMessage.Data())    

serialPort = Serial(port='/dev/tty.EV3-SerialPort', baudrate=9600)

send = Sender(serialPort) 
receive = Receiver(serialPort) 
send.start() 
receive.start()
    

        

To start a program you need to change the command to be a start program command. You can find more info on this and other direct commands here.

Anders

[Fergus O’Callaghan]

Yes I couldn’t really find an appropriate location for this question. Thanks anyway for the answer, I’ll try it out as soon as I can.

Fergus

[Anders Søborg]

No problem

Anders

[Pascal SALLIOT]

I’m trying to exchange mailbox’s messages between python 2.7 and the EV3’s software “LabVIEW” via a Bluetooth communication.
After several month searching, you’re the only one who was able to do this ; thank you for this work.

When I run the program above, I’ve got this message :

“SerialException(“could not open port %r: %r” % (self.portstr, ctypes.WinError()))
SerialException: could not open port ‘/dev/tty.EV3-SerialPort’: WindowsError(3, ‘Le chemin d\x92acc\xe8s sp\xe9cifi\xe9 est introuvable.’)”
It means that Windows is unable to find the path /dev/tty.EV3-SerialPort even if the brick is connected with the USB wire…

Any suggestions ?

[Author]

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