Interfacing with Python

There are many applications where you want to interface with mbed from a computer. Python is one language which you may wish to use. This page provides a library of code that can be used to communicate with mbed using RPC and a guide to set up Python.

Setup Python

On windows, install python, win32 extensions and pyserial (if you want to communicate using serial):

Run python-2.6.1.msi - Python Windows Binary
Run pywin32-212.win32-py2.6.exe - Python Win32 Extensions
Run pyserial-2.4.win32.exe - Python Serial Port Extension (gave some errors)

On Mac OS X (10.5 or later):

Python is already installed.
Run Terminal.app and type sudo easy_install pyserial at the prompt to install PySerial.
Also type ls /dev/tty.usbmodem* to find the device name of the mbed USB serial connection.

On Linux, or other unix-like:

Python is most-likely already installed; if not see your OS's install system or visit http://www.python.org/download/
In a terminal type sudo easy_install pyserial to install PySerial.
Also type ls /dev/ttyACM* to find the device name of the mbed USB serial connection.

Python RPC Library

The mbed libraries support RPC, which means you can create objects and control them remotely; Interfacing-Using-RPC.

mbedRPC.py

Here is a Python RPC library which uses the mbed RPC mechanism to map Python classes on to the mbed Library C++ Interface classes. The library is designed to be very similar to the mbed interface. This is an example using HTTP.

Python_mbed_HelloWorld

#!python
python
>>> from mbedrpc import *
>>> mbed = HTTPRPC("192.168.0.4")
>>> x = DigitalOut(mbed,LED1)
>>> z = DigitalOut(mbed,LED2) 
>>> ain = AnalogIn(mbed, LED3)
>>> x.write(1)
>>> z.write(0.5)
>>> ain.read()
0.786757474
>>>

The API

First of all you must import the mbedrpc library. To do this the mbedrpc.py file must be in the Python library.

You then create an mbed object on the transport mechanism that you require, (more information on this below). If you are using more than one mbed then create an object for each one passing the appropriate parameters to the transport mechanism for each.

Code

>>> mbed = HTTPRPC("192.168.2.2")
>>> mbed2 = HTTPRPC("192.168.2.3")

You can then create mbed interface objects in the same way as you would on mbed only you also have to pass them the mbed object which represents the mbed they are to be created on. This means you can control multiple mbeds.

Code

>>> x = DigitalIn(mbed, p20)

Alternatively you may wish to tie a Python object to an existing object on mbed in which case you pass in the name of that object.

Code

>>> y = DigitalOut(mbed, "myled")

Finally you can execute the methods on interface objects as defined in the Handbook.

Code

>>>x.read()
>>>y.write(1)

Information

If you want to execute an RPC command that isn't wrapped by the classes we've provided then use: RPCresponse = mbed.RPC(<Object name>,<Method name>,<Arguments as an array>)

Python RPC via HTTP

First you need code running on mbed to set up a HTTP server. Guidelines for this are in the Interfacing-Using-RPC page.

Once this is on the mbed, plug it in to your home router and power it up. With the serial port enabled, it should show the i/f comeing up, and print out the ip address that it has been assigned via DHCP.

Code

#!python
python
>>> from mbedRPC import *
>>> mbed = HTTPRPC("192.168.0.4")
>>> x = DigitalOut(mbed, LED3) # LED3
>>> x.write(1)
>>> x.read()
1
>>>

Python RPC via Serial

Test the Serial Connection

On Windows, connect to COM15 with default 9600 8N1 setting:

#!python
python
>>> import serial
>>> serdev = 15
>>> s = serial.Serial(serdev)
>>> s.write("hello")
>>> s.close()

or when on a Macintosh (in this case /dev/tty.usbmodem1912):

#!python
>>> import serial
>>> serdev = '/dev/tty.usbmodem1912'
>>> s = serial.Serial(serdev)
>>> s.write("hello")
>>> s.close()

or when on a Linux/unix system (in this case /dev/ttyACM0):

#!python
>>> import serial
>>> serdev = '/dev/ttyACM0'
>>> s = serial.Serial(serdev)
>>> s.write("hello")
>>> s.close()

Status light flickered. Cool!

For more basic info, see http://pyserial.wiki.sourceforge.net/pySerial

We know how to make Python talk to Serial. So if we set up mbed to receive RPC over serial then we can use this to control it. Again guidelines for setting up mbed to use serial RPC can be found here: Interfacing-Using-RPC

We can use the same mbedRPC.py file as before. We just need to set up the mbed object using SerialRPC rather than HTTPRPC

Code

#!python
python
>>> from mbedRPC import *
>>> serdev = 15 # or '/dev/tty.usbmodem1912' for Mac or '/dev/ttyACM0' for Linux/unix
>>> mbed = SerialRPC(serdev, 9600)
>>> x = DigitalOut(mbed, LED3) # LED3
>>> x.write(1)
>>> x.read()
1
>>>

Public Member Functions
template<class A >
	RPCVariable (A ptr, const char name)
	Constructor.
T	read ()
	Read the variable over RPC.
void	write (T value)
	Write a value to the variable over RPC.

Interfacing with Python

Setup Python

Python RPC Library

Python_mbed_HelloWorld

The API

Code

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Code

Information

Python RPC via HTTP

Code

Python RPC via Serial

Test the Serial Connection

Code

21 comments on Interfacing with Python:

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» Import this library into a program
RPCInterface - RPCVariable< T > Class Template Reference

Public Member Functions

Python_code

mbed_code

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Dan O'Brien wrote:

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Dan O'Brien wrote:

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Dan O'Brien wrote:

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J. Gerardo García wrote:

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Interfacing with Python

Setup Python

Python RPC Library

Python_mbed_HelloWorld

The API

Code

Code

Code

Code

Information

Python RPC via HTTP

Code

Python RPC via Serial

Test the Serial Connection

Code

21 comments on Interfacing with Python:

Code

Code

Code

Code

Code

» Import this library into a programRPCInterface - RPCVariable< T > Class Template Reference

Public Member Functions

Python_code

mbed_code

Code

Dan O'Brien wrote:

Code

Dan O'Brien wrote:

Code

Dan O'Brien wrote:

Code

J. Gerardo García wrote:

Code

Code

Code

Code

Code

Code

» Import this library into a program
RPCInterface - RPCVariable< T > Class Template Reference