How to Program Test Tools with Python - Workbench Wednesdays 66

I think you're using the wrong resource string.

This works for me on a DP831. Notice how my resource string includes USB0 and the serial number:

Connect the DP832 by USB. What does this output show:

import pyvisa
rm = pyvisa.ResourceManager('@py')
print(rm.list_resources())

And what does the output of `lsusb` on the command line show?

(Also if you press the Utility button on the DP832, it'll show you the USB resource string, in hex.)

Yes, I have already tried that, but it doesn't work. I don't know what could be the reason. Is there another method?

Specifying a baud rate shouldn't matter since it is a VCP connection.

Did you try just with the query delay?

In general, you shouldn't need to change the line terminations on VCP connections, so you should only try that if adding a query delay alone doesn't help.

Unfortunately, this method does not work, or I have done something wrong!

I cover multiple ways to can be solved in the video (timestamped):

https://youtu.be/1HQxnz3P9P4?t=638

First add a query delay and then second try changing the line terminators.

I tried to control both devices (DL3021 and DP832) via the USB interface, but I always receive the following error message:

Exception: VisaIOError VI_ERROR_TMO (-1073807339): Timeout expired before operation completed. In the file "/home/pi/my_project/env/PowerSupply_test.py", line 15, in <module>

print(supply.query("*IDN?"))         

^^^^^^^^^^^^^^^^^^^^^ pyvisa.errors.VisaIOError: VI_ERROR_TMO (-1073807339): Timeout expired before operation completed.

So keep in mind that a driver for the device and the "VISA driver" are separate things. The VISA driver talks to the OS drivers. So,if the OS cannot enumerate a device and provide a handle, then the VISA driver doesn't matter. So, this is not a NI-VISA issue.

Regardless, I am fairly certain Rigol uses either a libusb-based interface or emulates a USB-Serial device when connected by USB for all of their devices. I have never encountered one that does not work with Linux.

Compare the output of lsusb and what the pyvisa resource manager finds to verify what is getting enumerated.

Also, the R&S VISA drivers work great on Raspberry Pi. I've found their driver worked slightly better than pyvisa-py, regardless of the vendor's instrument.

I was able to communicate with the RIGOL DL3021 using the RS232 interface and program it with the Raspberry Pi 5 and Python. Unfortunately, it does not work over the USB interface because the Raspberry Pi cannot identify the instrument.

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