Using USB Based DAQ Devices on a Bus-Powered Hub

Issue Details

My computer has only 2 USB ports and I need to connect 3 devices. Since the USB Hub is a multidrop bus, where multiple devices can be connected to the bus at the same time, can I use one?

• Are there any specifications that I need to follow to ensure its success?
• Will there be any issues addressing the 3 different instruments in NI MAX?
• Will a DAQ device work with a bus-powered USB hub with different upstream and downstream port configurations?

Solution

NI recommends against using USB hubs, as the specifications all vary with each manufacturer. There are power and throughput limitations for each bus that are unknown. Even if the device appears to be functioning, the hub could lose data packets, which is out of the device's control. 

There are two kinds of USB hubs, bus-powered hubs and self-powered hubs. Bus-powered hubs receive all of their operational power from the USB bus, while self-powered hubs receive their operational power from an external power supply. 

Data acquisition devices can be used with bus-powered hubs, but in most cases this will require a power supply to power the hub's downstream ports. The power available to USB devices connected to a bus-powered hub decreases as more devices are connected. This decreased power level can become insufficient to power and operate some of National Instruments USB devices. In this case, the operating system will report an error, saying that there is insufficient power to run the device. 

A functional supply can be selected as specified by the hub's vendor. This requires that the device support a self-powered configuration where an external supply can be provided.
 

Additional Information

• Try to have minimal differences in USB version (ex. a USB 2.0 device should not be connected to USB 1.0 port)
• USB ports on peripherals such as keyboards or monitors are usually bus-powered. In this case, a separate, self powered hub is required.
• Ports on the back of the computer are typically self-powered.