Considerations when using USB2 cameras
Last Revision Date: 9/30/2015
This article outlines considerations for users of USB2 cameras. For additional information, see KB "Differences between USB 2.0 and USB 3.1 cameras."
The Universal Serial Bus (USB) 2.0 standard provides a high bandwidth 480 Mb/s interface that is well-suited for digital imaging, and is a well-established, popular serial interface. USB2 ports are widely available on a variety of hardware platforms, including Macintosh and PC systems, and a variety of laptop, desktop, and small form factor (embedded) systems. This availability maximizes system compatibility and minimizes the need for add-in PCI or PCI Express interface cards.
Most of the features familiar to users of our cameras are available on USB2 cameras, including:
- A "plug and play" camera system supported by FlyCapture API and SDK.
- Updatable firmware designed to the IIDC-1394-based Digital Camera Specification.
Nevertheless, when evaluating a USB 2 camera for purchase, it is important to be aware of the limitations of the interface.
Multiple cameras on the same bus: The USB standard allows for multiple USB devices on a single bus. However, we have not performed any rigorous qualification of the ability of various hardware platforms, operating systems, software, and drivers to handle multiple USB2 image streams, and we are therefore not able to address any questions directly or troubleshoot issues related to doing so. For more information, see KB "Troubleshooting problems when running multiple USB cameras on the same bus." Wherever possible, our USB3, GigE, and FireWire cameras should be used for applications that require multiple cameras running simultaneously on the same computer.
If you do wish to operate multiple USB cameras on one bus, keep in mind the following:
- Multiple Camera Synchronization: For reasons similar to the above, we do not support synchronizing multiple USB2 cameras on the same bus.
- Broadcast Properties: There is no support for broadcasting camera settings to other cameras on the same bus, including trigger and strobe broadcasting.
Other considerations for USB2 users:
- Cable Length: The standard cable length is 5 meters for USB devices.
- Power Requirements: USB2 cameras require a 4.75 V to 5.25 V power source. The maximum power restriction limits devices to sensors that consume less power and may output a narrower spectral response than higher voltage sensors.
- Bus speed: The speed of USB2 is 480 Mb/s, and is not configurable.
- Timestamp Precision: USB2 timestamps can range in accuracy from 0 to 125 µs at the end of shutter integration. This range can increase if there are higher priority threads running on the system.
- Partial image event notification: Our driver for USB2 cameras does not support partial imaging event notification, used for accessing image data in memory, before display.