Scratch graphical programming operation hardware

One , brief introduction

scratch It is a graphical programming software developed by MIT , This software provides the ability to use javascript And scratch Interface of interaction , It also provides a socket Ports and a series of commands interact with Applications , Here we explain how to pass python And scratch Interaction

Two , explain

The reason for choosing python It is mainly based on the following reasons ：
1,python Is a non compiled language , So unless the provider of the library will not want open source code written in C/C++, perhaps java And other compiled language code , And then through python call , In general, we can see the source code
2,scratch For the use of python Interact with it , Have a ready-made python Library can be called , So we don't need to know in detail scratch The cumbersome command structure defined externally , It doesn't make sense

3、 ... and , principle

1, When scratch When starting, the machine will be turned on by default 42001 The port is used as the server side socket Receive application requests （ This port Just the default , You can modify ）
2, We go through local socket Connect to scratch, Then you can send a series of commands and scratch Interaction , So we can go through scratch Graphical programming operates anything we want to operate , Like hardware

Four , Environment configuration

explain ： I do ubuntu below , Can be in similar linux It's all right on the distribution
1, install scratch: Be careful to install 1.4 Version of , What I installed on my machine with the following command is 1.4, If someone installs something other than 1.4 edition , I can't promise for the time being
sudo apt-get install scratch
2, install scratch Of python library
sudo apt-get install python-pip scratchpy
3, After installation, there is a scratch.py Of python Script , You can see scratch.py Code for , This is provided through python operation scratch All interfaces and commands

5、 ... and ,scratch.py Provided interface

The following post scratch.py Part of the code we use here ： You can see if you are interested scratch.py Source code

import array
import errno
import itertools
import socket
import struct

class ScratchError(Exception): pass
class ScratchConnectionError(ScratchError): pass        

class Scratch(object):

    prefix_len = 4
    broadcast_prefix_len = prefix_len + len('broadcast ')
    sensorupdate_prefix_len = prefix_len + len('sensor-update ')

    msg_types = set(['broadcast', 'sensor-update'])

    def __init__(self, host='localhost', port=42001):
        self.host = host
        self.port = port
        self.socket = None
        self.connected = False
        self.connect()

    def connect(self):
        """ Connects to Scratch. """
        self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        try:
            self.socket.connect((self.host, self.port))
        except socket.error as (err, msg):
            self.connected = False
            raise ScratchError("[Errno %d] %s" % (err, msg))
        self.connected = True

    def broadcast(self, msg):
        if getattr(msg, '__iter__', False): # iterable
            for m in msg:
                self._send('broadcast "%s"' % self._escape(str(m)))
                print "hjptestfor:",self._escape(str(m))
        else: # probably a string or number
            self._send('broadcast "%s"' % self._escape(str(msg)))
            print "hjptestfor:",self._escape(str(msg))

    def receive(self):
        return self._parse(self._recv())

1, We can see the used port The port is 42001, yes host yes “localhost”( Description remote connection is not supported ), Of course, we can use our application as a springboard , Then operate remotely scratch, It's all a postscript
2, We can also translate the above code into other languages, such as C Language, etc. , Of course, since there is already this library, there is no need , Interested as a kind of trial practice

6、 ... and , Our example

The code is as follows ：

#filename:helloscratch.py
import scratch
try:
      s = scratch.Scratch()
      if s.connected:
            print "Connected to Scratch successfully"
      else:
            print "Connected to Scratch error"
except scratch.ScratchError:
      print "Scratch is not opened or remote sensor connections aren't enabled"


try:
      print "broadcast begin"
      s.broadcast('hello scratch')
except NameError:
      print "Scratch: Unable to Broadcast"

while True:
      try:
            msg = s.receive()
            print "Scratch: receive:",msg
      except KeyboardInterrupt:
            print "GrovePi Scratch: Disconnected from Scratch"
            break

The main function of this code is to scratch Print out the sent string , To operate the hardware , We can customize a set of commands , such as i2c,address etc. , When we receive these strings, we can operate the hardware in our client （ Of course, this example is just printing ）
For example, to operate i2c, Just execute sudo apt-get install python-smbus That's all right. ,

7、 ... and , Running effect

perform ： First, start it manually scratch, Otherwise, our client will fail to connect because the server is not online
stay shell Input directly ：scratch Enter and start scratch

And then in shell Run our client under , It's connected to scratch：
suso python helloscratch.py
That's it with us shell Interaction
For example, we add the following module

When we click on the flag scratch Graphic code runs , Received on our client 112 This string , The effect is as follows ：

If you need to operate the hardware , You can put it in join It defines its own commands ： After receiving these command strings , Then operate the hardware , This has the effect of operating the hardware