[OpenTRV-dev] python opentrv to emoncms script...

[Bruno Girin]

Bo,

The data is JSON. However, because of the way your code reads the data, it
starts reading the beginning of the second line. See the additional { in
the message (first character second line):

{"@":"151f","+":4,"T|C16":336,"O":1,"vac|h":94,"v|%":0}
*{*Traceback (most recent call last):

So you need to add detection of the newline in your code to ensure that the
string you pass to json.loads is a single line and if you have more
characters after that newline, push them to the next. A good way to do this
would be using a generator function, so something like:

def read_lines_from_serial(ser):
    while 1:
       # Read from serial port, blocking
       data = ser.read(1)

       # If there is more than 1 byte, read the rest
       n = ser.inWaiting()
       if n:
           data = data + ser.read(n)
           lines = data.splitlines()
           # iterate over all lines except the last one
           # (will do nothing if no newlines in data)
           for l in lines[:-1]:
               yield l
           # assign the last line to data so that we can keep appending to
it
           data = lines[-1]

Then you should be able to call your function like this:

for d in read_lines_from_serial(ser):
    j = json.loads(d)
    # do whatever is sensible with j


On 6 October 2015 at 21:40, Bo Herrmannsen <bo.herrmannsen at gmail.com> wrote:

> could it be that the data is not json but just looks like it?
>
> 2015-10-06 22:00 GMT+02:00 Bo Herrmannsen <bo.herrmannsen at gmail.com>:
>
>> now the script is:
>>
>> import sys
>> import serial
>> import json
>>
>> port = "/dev/ttyUSB0"
>> baud = 4800
>>
>> ser = serial.Serial()
>> ser.port = port
>> ser.baudrate = baud
>>
>> try:
>>    ser.open()
>> except:
>>    sys.stderr.write("Error opening serial port %s\n" % (ser.portstr) )
>>    sys.exit(1)
>>
>> ser.setRtsCts(0)
>>
>> while 1:
>>    # Read from serial port, blocking
>>    data = ser.read(1)
>>
>>    # If there is more than 1 byte, read the rest
>>    n = ser.inWaiting()
>>    if n:
>>        data = data + ser.read(n)
>>
>>
>>
>>    sys.stdout.write(data)
>>
>>    if data.startswith('{'):
>>
>>     j = json.loads(data)
>>     print j['@']
>>
>>
>>
>> my logic is to print what comes in from serial and that part works fine
>>
>> i then want to build on it and if we have a json string then write just
>> the units id...
>>
>> the last part is failing me.. i get:
>>
>>
>> {"@":"151f","+":4,"T|C16":336,"O":1,"vac|h":94,"v|%":0}
>> {Traceback (most recent call last):
>>   File "opentrvimport.py", line 35, in <module>
>>     j = json.loads(data)
>>   File "/usr/lib/python2.7/json/__init__.py", line 326, in loads
>>     return _default_decoder.decode(s)
>>   File "/usr/lib/python2.7/json/decoder.py", line 365, in decode
>>     obj, end = self.raw_decode(s, idx=_w(s, 0).end())
>>   File "/usr/lib/python2.7/json/decoder.py", line 381, in raw_decode
>>     obj, end = self.scan_once(s, idx)
>> ValueError: Expecting object: line 1 column 0 (char 0)
>>
>>
>> 2015-10-06 17:05 GMT+02:00 Bo Herrmannsen <bo.herrmannsen at gmail.com>:
>>
>>> Hi
>>>
>>> I started on a script that can read serial data from a rev2 unit and
>>> send the data on to emoncms.
>>>
>>> i get this on the serial line
>>>
>>> {"@":"2800","+":4,"T|C16":544,"vC|%":2340,"O":1}
>>>
>>>
>>> and so far i have this python script
>>>
>>>
>>> import serial
>>> import io
>>> import time
>>> ser = serial.Serial('/dev/ttyUSB0',4800)
>>>
>>>
>>> sio = io.TextIOWrapper(io.BufferedRWPair(ser, ser, 1),
>>> encoding='ascii',newline='\r\n')
>>>
>>> while ser.isOpen():
>>>
>>>           datastring = sio.readline()
>>>
>>> print datastring
>>>
>>>
>>>
>>>
>>> the serial data end with CRLF
>>>
>>> but it does not print anything.... where am i wrong?
>>>
>>> before i used this script:
>>>
>>> import serial
>>> import time
>>> s = serial.Serial('/dev/ttyUSB0',4800)
>>>
>>> while 1:
>>>    if s.inWaiting():
>>>       val = s.read(s.inWaiting())
>>>       print val
>>>
>>> but then i got:
>>>
>>> {"@":"0950","
>>> +":
>>> 5,"
>>> t
>>> T|C
>>> ":
>>> 1
>>> 9,"
>>> vC|%
>>> ":
>>> 20
>>> 0,"
>>> T|
>>> C
>>> 1
>>> 6":
>>> 33
>>> 1}
>>>
>>>
>>>
>>>
>>
>
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>
>
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