Sending commands to temperature monitor; b'\xab', why?

[CJA (Christopher Alvarez)]

Working on send commands to a temperature monitor. Fiddled a bit and got the following. Not sure what it means or how to convert to usable data (if there is any). Any ideas?

import serial
 
ser.close()
ser = serial.Serial(port='COM5',\
                   baudrate=9600,\
                   parity=serial.PARITY_NONE,\
                   stopbits=serial.STOPBITS_ONE,\
                   bytesize=serial.EIGHTBITS,\
                    timeout=2)
 
print("connected to: " + ser.portstr)
#ser.close()
count=1

while True:
#line = ser.readline()
#print(str(count) + str(': ') + str(line))
#count = count+1
    cmd = input("Enter command or 'exit':")
        # for Python 3
    if cmd == 'exit':
        ser.close()
        quit()
    else:
        ser.write((cmd+'\r\n').encode('utf-8'))
        out = ser.read()#.decode('utf-8')
        print(out)#.decode('utf-8'))
ser.close()

Output is

connected to: COM5
Enter command or ‘exit’: KRDG? 1
b’\xab’

Wondering what b’\xab’ could mean

[barry-scott]

Please replace your picture of text with preformated text that is easier for us to read and quote from to help you.

Use the </> button to quote text.

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[MRAB (Matthew Barnett)]

You need to consult the documentation of the temperature monitor.

[cameron (Cameron Simpson)]

Just a note that Serial.read has a default read size of 1.

Maybe try adding a timeout to the Serial setup and doing a longer
read. You might get a more intelligible result. BTW do you know about
what temperature you expect to get?

There’s also Serial.read_until which could be useful if you’re
expecting a “line” of data as a response.

But Matthew’s point is important: what does the documentation say you
should get?

Cheers,
Cameron Simpson cs@cskk.id.au

[barry-scott]

What is the hardware that you are connecting to?
Do you have a link to its documentation?

[CJA (Christopher Alvarez)]

Thanks Cameron, I’ll give it a shot. It’s a temperature monitor and should be reading out around room temp, currently hovering at ~292.45K

[CJA (Christopher Alvarez)]

I’m connecting to a Lakeshore 218e Temperature Monitor, which has only the RS232 and not the IEEE-488 interface.

User Manual:
218_v2.0.doc (lakeshore.com)
Remote Operation is section 6 (p 65).

Specs:
Model 218 Temperature Monitor (lakeshore.com)

[abessman (Alexander Bessman)]

From the manual:

6.2.3 Character Format
A character is the smallest piece of information that can be transmitted by the interface. Each character is 10 bits long and contains data bits, bits for character timing and an error detection bit. The instrument uses 7 bits for data in the ASCII format. One start bit and one stop bit are necessary to synchronize consecutive characters. Parity is a method of error detection. One parity bit configured for odd parity is included in each character.

Your instrument uses 7 data bits and one parity bit (odd). You should configure your serial interface like so:

ser = serial.Serial(port='COM5',\
                   baudrate=9600,\
                   parity=serial.PARITY_ODD,\
                   stopbits=serial.STOPBITS_ONE,\
                   bytesize=serial.SEVENBITS,\
                    timeout=2)

Edit: Assuming the final bit is a parity bit, b'\xab' is actually b'\+'. If you read more bytes, numbers are likely to follow.

[CJA (Christopher Alvarez)]

Alexander, my man!! I really should have caught the parity and byte params. Matched them up in the device manager, too. Now to get it to return a string, rather than single characters. Thanks bud!!

[CJA (Christopher Alvarez)]

Bingo! Thanks Cameron!