If using the FTDI USB Drivers to allow a device to communicate with the USB port (and subsequently a software application), then sometimes you may run into ‘device not found’ type errors, even if the same device was used on that same computer recently. This could be a result of virtual port assignments and how Windows manages Com Port assignments from FTDI USB devices.
When a device is connected to a Windows PC, the device is identified by 3 variables: VID, PID and Serial Number. When this device is connected for the first time, Windows will automatically assign it an available virtual port. If you have 3 of the same device, for example, 3 ACME Mini-weather stations that use the FTDI drivers, then each one of these devices will receive a different USB port assignment. The devices are the same, but they have different VID, PID, and Serial Numbers. Com Port Name Arbiter is defined within:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter\ComDB
Depending on the software application used to ‘talk’ to your external USB device, in some cases, the device may not be recognized due to a port assignment conflict or because Windows assigned a port number not used by the application for intial connection. These port assignments can be checked and changed within Windows Device manager:
Check the device within Device Manager.
1. Launch Computer Management -> Click Windows START button -> Right Click ‘My Computer’ then select ‘Manage’.
2. Select Device Manager.
3. Connect the device to the Computer’s USB and note which port it is assigned. (See Image)
4. In this example, Com ports 1-9 are the only ports recognized by the application and since Device Manager assigned the port Com13, the device will not be recognized. (See Image)
Change port assignment.
1. Right click the device in Device Manager and select ‘Properties’.
2. Select ‘Port Settings’, then ‘Advanced’, then ‘Com Port Number’ and select a different available port. (See Image)
3. Click ‘OK’.
4. Relaunch the device application and verify.