Question

Buongiorno, I m trying to send a simple string to a serial port to command an instrument for noise measures.
The strings are very easy:
"M 1" = instrument on
"M 2" = instrument off
"M 3" = begin the measure
"M 4" = stop the measure

I ve found this program:

import serial

ser = serial.Serial(0)  #Seleziona la porta seriale COM4
ser.baudrate = 9600 #Imposta il baudrate a 9600bps

ser.open() #apre la porta com
ser.close() 
#verifica se la porta e  aperta
if ser.isOpen():
   com_num = ser.portstr
   print ("Porta " + com_num + " aperta")
   #invia il comando alla seriale
   buffer = "M 3"
   ser.write(buffer)     
   #Loop d attesa caratteri
   num = 0
   while num == 0:
       num = ser.inWaiting()
   #scarica il buffer della seriale
   buffer = ser.read(num)
   print ("Dati ricevuti dalla seriale:")
   print buffer
   ser.close()             #chiude la porta
else:
   print ("Porta seriale gia  in uso o inesistente") 
s = raw_input("digita INVIA per uscire")

USING LINUX
The program is ok and I have only some problems with the type of string. In fact I had to insert a carriage return but I can t to do it.
I said that the program is okay because the instrument turn from off to on when I made my first connection, and on video I read "Porta /dev/ttyS= aperta" thet means "open". But this appens for any kind of string I send. In fact this is like an "iniatilization" of the port, not a really communication.
Then I don t manage to send string in the correct way, may be for the problem of carriage return.

USING WINDOWS
I can t open the port, I have an error of Denied Access to the port, this is the error:
Traceback (most recent call last): File "C:/d.py", line 9, in ser.open() #apre la porta com File "C:ProgrammiPython26libsite-packagesserialserialwin32.py", line 53, in open raise SerialException("could not open port %s: %s" % (self.portstr, ctypes.WinError())) serial.serialutil.SerialException: could not open port COM1: [Error 5] Accesso negato.

Can you help me to:
1. Manage to run the program under windows
2. Manage to give in the exactly way the string with carriage return???

Thak you very much.
Stefano

Answer 1

To add the carriage return just append to your string, or perhaps, it may need a carriage return/linefeed , which some systems use to mark the end of line. Of course, it may only need a linefeed. In that case, you would simply use .

buffer = "M 3
"

or

buffer = "M 3
"

or

buffer = "M 3
"

You might find the pySerial documentation of help in resolving your Windows issues.

Answer 2

Unfortunately it doesn t work.
In the past I ve already tried to use with the command echo in linux via bash... but nothing.
Now I m trying with python but nothing again. It may be interesting that the instrument, when I give the string in this way:

buffer = "M 3 "
or
buffer = "M 3 "

gives to me this answer: @

That s all...
I don t know.
Another thing: when I ve tried with the bash language the instrument begins the measure with the command:
echo "M 3 " > /dev/ttyS0
that is with a blanck after 3.
Obviously the other command don t work with this strange blanck...

Thank you very much!

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