Multiple HID devices with same VID PID

[bobdring]

Hi,
This is my first post.

I'm more of a HW guy but I need some SW info.

I want to write a 'data logging' program for a number of USB connected Digital Multi Meters (DMMs). They are Victor model 86C
They appear to be recognised by Windows as of the HID type.

My question is, If the DMMs all have the same VID and PID can they be accessed without any confusion?

The DMM comes with data logging SW but it only handles 1 DMM and if I run multiple copies of the SW it get confused and often logs the same meter in each copy.

Bob

[Jan Axelson]

Applications can handle multiple, identical HIDs, but to do so, they need to search for all of the devices and open a handle to each or provide a means for the user to pick one. It sounds like your software selects the first device found and uses that. For system mice and keyboards, the OS treats all devices as one virtual device, but I don't think that is your situation.

Jan

[bobdring]

Jan,
Thanks for the reply.

If I understand you. When a DMM is connected the actual USB connector used to connect it has no fixed identifier in the open function. This means the SW has no knowledge of which DMM is which and the user would have to identify the DMM to the SW. I guess disconnecting an reconnecting DMMs would require that they be 're-identified'.

You are correct, the supplied software finds the first DMM connected. I can work around it by only having one DMM connected when I start the second copy of the SW. Unfortunately if I pause logging, disconnect the USB cable or change the range switch on the DMM the SW closes the port and reopens it. While I have 4 DMMs I can only trick it into logging from 2 at a time. I think I will contact Victor and see if they will 'fix' this port closing or perhaps they might offer me the source so that I can fix it myself.

You have saved me many hours of frustration with your reply. Once again thanks.

Bob

[Jan Axelson]

Yes, I think you'll need a software revision from the software provider.

Jan