Servo - April 2009

COMPUTER CONTROL and DATA ACQUISITION

by David A. Ward

Part 2: An Introduction to

National Instruments USB-6008 Data Acquisition Hardware

Part 1 introduced National Instruments LabVIEW software and had the reader build a very simple VI (virtual instrument). This article will introduce National Instrument’s most affordable computer interfacing hardware — the USB-6008( 9) data acquisition units — and show how to use the digital features of the units.

On the computer interfacing hardware side, NI offers many options, however, at the entry level the most affordable are the USB-6008( 9) units. The USB-6008 student version sells for $170 and the USB-6009 sells for $280. These two units look identical on the outside (see Photo 1), however, the 6009 unit has several enhanced features that the 6008 does not have. First, the 6009 has a faster analog sampling rate — 48 ks/s versus 10 ks/s (thousands of samples per second). Secondly, the 6009 has a higher resolution analog-to-digital converter (A-to-D); 14 bits versus 12 bits. Thirdly, the USB-6009 digital outputs can be set up as either push-pull or open-drain; the USB-6008 digital outputs can only operate as open-drain.

I have worked with both units and believe that the less expensive USB-6008 will handle any task that an entry level user would require. Therefore, all of the examples given in this article and those that follow will be with the USB-6008, although everything should work fine on the USB-6009.

Let’s take a closer look at all of the features available on the units. Each is divided between an analog side and a digital side. On the digital side, they have two digital I/O ports that are CMOS, TTL, and LVTTL compatible. Port0 has eight digital terminals; P0.0 through P0.7. Port1 has four digital terminals; P1.0 through P1.3. The 12 digital I/O terminals can be individually configured as inputs or outputs, and as was mentioned earlier there is a difference between the types of outputs each unit can provide. There is another terminal, PFI0, that is connected to a 32-bit counter that can count