Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #19943 > unrolled thread

how to read serial stream of data [newbie]

Back to article view | Back to comp.lang.python

Contents

  how to read serial stream of data [newbie] Jean Dupont <jeandupont115@gmail.com> - 2012-02-06 13:40 -0800
    Re: how to read serial stream of data [newbie] Roy Smith <roy@panix.com> - 2012-02-07 00:07 -0500
      Re: how to read serial stream of data [newbie] Jean Dupont <jeandupont115@gmail.com> - 2012-02-07 04:13 -0800
        Re: how to read serial stream of data [newbie] Antti J Ylikoski <antti.ylikoski@tkk.fi> - 2012-02-07 15:48 +0200
          Re: how to read serial stream of data [newbie] Peter Otten <__peter__@web.de> - 2012-02-07 15:02 +0100
            Re: how to read serial stream of data [newbie] Antti J Ylikoski <antti.ylikoski@tkk.fi> - 2012-02-07 19:44 +0200
          Re: how to read serial stream of data [newbie] Heiko Wundram <modelnine@modelnine.org> - 2012-02-07 15:04 +0100
            Re: how to read serial stream of data [newbie] Jean Dupont <jeandupont115@gmail.com> - 2012-02-07 06:46 -0800
        Re: how to read serial stream of data [newbie] Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-02-07 12:44 -0500

#19943 — how to read serial stream of data [newbie]

I'd like to read in a stream of data which looks like this:
the device sends out a byte-string of 11 bytes roughly every second:

    B0B0B0B0B03131B0B50D8A
    B0B0B0B0B03131B0B50D8A
    B0B0B031B63131B0310D8A
    B0B034B3323432B3310D8A
    B0B03237B53432B3310D8A
.
.
.

As you see every string is ended by 0D8A
How can this be accomplished in Python?


thanks

Jean

[toc] | [next] | [standalone]

#19948

In article 
<e84f3af4-da6d-4ae9-8974-54354ec16307@b18g2000vbz.googlegroups.com>,
 Jean Dupont <jeandupont115@gmail.com> wrote:

> I'd like to read in a stream of data which looks like this:
> the device sends out a byte-string of 11 bytes roughly every second:
> 
>     B0B0B0B0B03131B0B50D8A
>     B0B0B0B0B03131B0B50D8A
>     B0B0B031B63131B0310D8A
>     B0B034B3323432B3310D8A
>     B0B03237B53432B3310D8A
> .
> .
> .
> 
> As you see every string is ended by 0D8A
> How can this be accomplished in Python?

The basic idea would be to open your datastream in binary mode 
(http://docs.python.org/library/functions.html#open), then use read(11) 
to read exactly 11 bytes into a string.

Depending on what the 11 bytes are, you might want to use the struct 
module (http://docs.python.org/library/struct.html) to extract the data 
in a more useful form.

[toc] | [prev] | [next] | [standalone]

#19954

On 7 feb, 06:07, Roy Smith <r...@panix.com> wrote:
> In article
> <e84f3af4-da6d-4ae9-8974-54354ec16...@b18g2000vbz.googlegroups.com>,
>  Jean Dupont <jeandupont...@gmail.com> wrote:
>
> > I'd like to read in a stream of data which looks like this:
> > the device sends out a byte-string of 11 bytes roughly every second:
>
> >     B0B0B0B0B03131B0B50D8A
> >     B0B0B0B0B03131B0B50D8A
> >     B0B0B031B63131B0310D8A
> >     B0B034B3323432B3310D8A
> >     B0B03237B53432B3310D8A
> > .
> > .
> > .
>
> > As you see every string is ended by 0D8A
> > How can this be accomplished in Python?
>
> The basic idea would be to open your datastream in binary mode
> (http://docs.python.org/library/functions.html#open), then use read(11)
> to read exactly 11 bytes into a string.
>
> Depending on what the 11 bytes are, you might want to use the struct
> module (http://docs.python.org/library/struct.html) to extract the data
> in a more useful form.

Thank you very much for taking the time to reply. I'm really
completely new to python and all help is really very welcome.
In the documentation I read that to open the datastream binary I need
to add the option b
this is how far I got until now:
#!/usr/bin/python
import serial, time, os
voltport='/dev/ttyUSB2'
print "Enter a filename:",
filename = raw_input()
voltdata = open(filename,'wb')
ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
rtscts=0, dsrdtr=0, timeout=15)
ser2.setDTR(level=True)
print "State of DSR-line: ", ser2.getDSR()
#the following line was added because I want to be sure that all
parameters are set the same as under a working application for the
same device
os.system("stty -F31:0:bbb:
0:0:0:0:0:0:0:1:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0")
print "Opening " + ser2.portstr
s =ser2.read(11) #read up to 11bytes
voltdata.write(s)
ser2.close()
voltdata.close()

However the above code doesn't fill my file with data, I guess the
data should also be flushed somewhere in the code but I'm unsure where
to do that.
A futher consideration: because the device sends its data continuously
I guess I'd have to use the byte sequence 0D8A of the previously sent
data string as an indicator that the next 9 bytes are those I really
want and put those in a string which than coudl be written to the file

all help welcome
Jean

[toc] | [prev] | [next] | [standalone]

#19957

On 7.2.2012 14:13, Jean Dupont wrote:
> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
> rtscts=0, dsrdtr=0, timeout=15)

In Python, if you want to continue the source line into the next text 
line, you must end the line to be continued with a backslash '\'.

So you should write:

ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1, \
rtscts=0, dsrdtr=0, timeout=15)

and analogously.

Hope that this will help.  Andy.

[toc] | [prev] | [next] | [standalone]

#19958

Antti J Ylikoski wrote:

> On 7.2.2012 14:13, Jean Dupont wrote:
>> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
>> rtscts=0, dsrdtr=0, timeout=15)
> 
> In Python, if you want to continue the source line into the next text
> line, you must end the line to be continued with a backslash '\'.
> 
> So you should write:
> 
> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1, \
> rtscts=0, dsrdtr=0, timeout=15)
> 
> and analogously.
> 
> Hope that this will help.  Andy.

This is wrong. A line with an open parenthesis is continued automatically:

>>> zip("abc",
... "def")
[('a', 'd'), ('b', 'e'), ('c', 'f')]
>>> ("abc"
... "def")
'abcdef'
>>> 1 + 2 + (
... 3)
6

[toc] | [prev] | [next] | [standalone]

#19967

On 7.2.2012 16:02, Peter Otten wrote:
> Antti J Ylikoski wrote:
>
>> On 7.2.2012 14:13, Jean Dupont wrote:
>>> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
>>> rtscts=0, dsrdtr=0, timeout=15)
>>
>> In Python, if you want to continue the source line into the next text
>> line, you must end the line to be continued with a backslash '\'.
>>
>> So you should write:
>>
>> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1, \
>> rtscts=0, dsrdtr=0, timeout=15)
>>
>> and analogously.
>>
>> Hope that this will help.  Andy.
>
> This is wrong. A line with an open parenthesis is continued automatically:
>
>>>> zip("abc",
> ... "def")
> [('a', 'd'), ('b', 'e'), ('c', 'f')]
>>>> ("abc"
> ... "def")
> 'abcdef'
>>>> 1 + 2 + (
> ... 3)
> 6
>
>

Thank you for correcting me.  Andy.

[toc] | [prev] | [next] | [standalone]

#19959

Am 07.02.2012 14:48, schrieb Antti J Ylikoski:
> On 7.2.2012 14:13, Jean Dupont wrote:
>> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
>> rtscts=0, dsrdtr=0, timeout=15)
>
> In Python, if you want to continue the source line into the next text
> line, you must end the line to be continued with a backslash '\'.

Absolutely not true, and this is bad advice (stylistically).

When (any form of) brackets are open at the end of a line, Python does 
not start a new command on the next line but rather continues the 
backeted content.

So:

ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
                      rtscts=0, dsrdtr=0, timeout=15)

is perfectly fine and certainly the recommended way of putting this.

Adding the backslash-continuation is always _possible_, but only 
_required_ when there are no open brackets.

So:

x = "hello" \
     " test"

is equivalent to:

x = ("hello"
      " test")

in assigning:

x = "hello test"

-- 
--- Heiko.

[toc] | [prev] | [next] | [standalone]

#19961

On 7 feb, 15:04, Heiko Wundram <modeln...@modelnine.org> wrote:
> Am 07.02.2012 14:48, schrieb Antti J Ylikoski:
>
> > On 7.2.2012 14:13, Jean Dupont wrote:
> >> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
> >> rtscts=0, dsrdtr=0, timeout=15)
>
> > In Python, if you want to continue the source line into the next text
> > line, you must end the line to be continued with a backslash '\'.
>
> Absolutely not true, and this is bad advice (stylistically).
>
> When (any form of) brackets are open at the end of a line, Python does
> not start a new command on the next line but rather continues the
> backeted content.
>
> So:
>
> ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
>                       rtscts=0, dsrdtr=0, timeout=15)
>
> is perfectly fine and certainly the recommended way of putting this.
>
> Adding the backslash-continuation is always _possible_, but only
> _required_ when there are no open brackets.
>
> So:
>
> x = "hello" \
>      " test"
>
> is equivalent to:
>
> x = ("hello"
>       " test")
>
> in assigning:
>
> x = "hello test"
>
> --
> --- Heiko.

Hello to all who gave advice concerning the line continuation, in fact
this was not a real problem but happened by accident
copying and pasting my program lines. Advice concerning the empty file
would of course also be very much appreciated.

thanks,
Jean

[toc] | [prev] | [next] | [standalone]

#19968

On Tue, 7 Feb 2012 04:13:39 -0800 (PST), Jean Dupont
<jeandupont115@gmail.com> wrote:


>filename = raw_input()
	Note: this may include the terminating new-line character; you
should strip leading/ending white-space characters.

	filename = raw_input().strip()

>ser2 = serial.Serial(voltport, 2400, 8, serial.PARITY_NONE, 1,
>rtscts=0, dsrdtr=0, timeout=15)
	Note: this specifying NO FLOW CONTROL (your PERL example is
activating DTR, which could be both enabling DSRDTR control, AND setting
the DTR line high). Finally, you are specifying a 15 SECOND timeout.

>ser2.setDTR(level=True)
	Note: here you are setting the DTR level high -- but you previously
opened the port without enabling the use of DSRDTR. Use
			...,	dsrdtr=True, ...
in the serial port creation.

>print "Opening " + ser2.portstr

	ser2.name		is the preferred usage; and you opened it with the
serial.Serial() call. And for such debug output, no need for a string
concatenation

	print "Reading", ser2.name

>s =ser2.read(11) #read up to 11bytes

	print len(s), repr(s)

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web