For quite a few years I've been using an ASI120mm as a very good guide camera, I then decided to buy another ASI120mm for an all sky camera project with both connected to my observatory computer.
That is when I realized to allow one camera to work I had to disconnect the other and vice- versa, simply because they use the same driver.
I then bought a USB "A /B" switch box which would "presumably" allow me to alternate between each camera so I would not have to unplug any of them, that's when I came across a major issue:
One of the ASI120mm camera's is now no longer recognized by windows ( O.S. Windows 7 Pro) - I have uninstalled drivers, tried using the camera on another computer (which incidentally) the camera worked fine on previously, it looks like the firmware has become corrupted?
As the Monty Python parrot sketch so eloquently put's it :
"The camera is as dead as a parrot - , it has gone to meet it's maker, it has ceased to exist."
I friend of mine brought his ASI120mm-S (USB 3) for me to try, I have installed the latest drivers for the camera , plugged the camera in and discovered the following issue's when using both Firecapture and Sharpcap :
In Firecapture : only the ASI120mm ( USB 2 ) camera was recognized.
In Sharpcap : 2 instances of "ASI120mm" were detected - I selected the first ASI120mm in the list and the guide camera was activated.
I then disconnected the camera and then selected the second ASI120mm and the guide camera activated yet again?
In Device manager both the ASI120mm and ASI120mm-s are showing up as being installed ( see included image)
To allow each camera to work individually I have to disable one of the camera's in the device manager.
Unless I am incorrect this tells me that both camera's are using the same driver ?
If that is not the case : Why can't I have 2 instances of Fire capture or Sharpcap working simultaneously with both camera's?
Finally - I intend to keep using the ASI120mm as a guide camera , can you please tell me which camera would be suitable as an all sky camera which has a PROVEN record of operating simultaneously with an ASI120mm (USB 2) on Windows 7 Pro. O.S..
In a few years time when the planets are more suitably placed I intend to buy another camera so ideally this camera too would have to work alongside the ASI120mm and an all sky camera without having to unplug any of them.
I am not sure your problem.
On our side, 2 120MM should works together, there is no need to turn off one when the other one works. You can see my attachment. I tested with 2 120MC. Just one thing need to pay attention, the USB bandwidth for USB2.0 is very small, so you need to take care of your USB traffic.
For the 120S, it also should works with 120MM.