USB data acquisition systems

- an overview about the use of USB data acquisition systems, how USB can be used for data acquisition, its advantages and limitations.

The USB (Universal Serial Bus) provides an ideal method of providing connectivity between a computer and remote sensors for data acquisition. As a result USB data acquisition modules and devices are now widespread on the market. The use of USB has grown in all sectors of the computer market as a result of its convenience. In line with this the data acquisition sector has also used the interface for small and cost effective devices.

USB data acquisition advantages

Not only has USB proved itself an ideal platform for many mainstream computer applications, but it also offers many advantages for data acquisition systems. The advantages include aspects including:

  • USB allows much faster speeds than RS232
  • The power for the "sensor" or data acquisition module can be obtained from the computer, simplifying many systems, and especially any portable USB data acquisition systems.
  • USB data acquisition modules can be connected and disconnected without the need to power down the computer
  • USB ports are standard on most PCs these days making it an almost universally available method of connection.
  • It is possible to use USB as well as other data acquisition communication standards together
  • It is possible to expand the connectivity using a USB hub so that several USB data acquisition devices can be connected

USB data acquisition products

There is a considerable number of different USB data acquisition products that are available. Although dedicated measurement modules may be available, other items may be capable of taking in a variety of analogue and digital inputs. These items are particularly useful in applications where a number of points and sensors need to be monitored. Also, having a multiple input USB data acquisition module means that only one module may be required. These modules may also come with their own data acquisition software.

A further advantage of this form of data acquisition module is that only one module may be required. If several modules are needed, then ultimately the power supply on the computer may become overloaded.

Cable for USB data acquisition

While many USB devices may plug directly in to the host computer it is possible to use an extender cable. The maximum allowable length for an individual cable is 5 metres (3 metres for slow devices) and this allows the USB data acquisition module to be located remotely from the computer.

A USB cable has two forms of connector. These are designated the "A" and "B" connectors. The connections to the connectors are given below:

Pin Function
1 Vbus
4.75 - 5.25 V
2 Data -
3 Data +
4 Ground
Shell Screen

USB cable pin assignments

USB data acquisition cards provide a very attractive solution to many data acquisition applications. Often compact modules are available and these can be connected to virtually any PC very easily. Not only is the connection simple, but a USB data acquisition system can be extended relatively easily by using a USB hub to enable further units to be connected.

By Ian Poole

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