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The Universal Serial Bus is not universal.  However, it offers advantages that may make it well worth consideration.  One of these is so called, "Hot Swapping," where devices on the bus may be connected and disconnected from the host PC while power is applied, without concern about damage to either the PC or the USB device.  Another is "Plug and Play" operation.  Thus, a USB device is automatically detected when it is connected.  If the proper device drivers have been installed, the USB device automatically becomes available.

USB devices do not occupy a PC bus slot, nor do they require that the user open the PC to connect them.  This makes them attractive in a number of applications, especially ones that might use a notebook computer.

USB offers high raw data rates (as high as 12M bytes per second in current incarnations).  The actual acquisition sample rate is, of course, dependent on much more than the raw serial bus speed.

Here is an article from Test and Measurement World on the subject.  USB Proves Ready for T&M Tasks.  A more recent and in-depth article is from Evaluation Engineering titled, Using USB as a Data Acquisition Interface.

Low-cost (under $100) options are Phidgets: 1011 - PhidgetInterfaceKit 2/2/2 and 1046 - PhidgetBridge 4-Input with two and four inputs, respectively, and DLP Design: DLP-IO8-G 8-Channel Data Acquisition Board,for only $30 - very low cost, but with modest performance.

A fairly high performance USB based data acquisition system is from DATAQ Instruments.  Their DI-720 and DI-730  portable units range in price from US$1200 to US$3200.

IOTech USB Data Acquisition Modules Models /55 and /56 come with software that includes drivers for Visual Basic.  Prices range from US$700 to US$1000.  Here is an article from Evaluation Engineering magazine that discusses some features of USB data acquisition by an IOTech representative.  Connecting With the New Universal Serial Bus

Data Translation DT9800 series USB data acquisition modules range in price from US$900 to US$1200.

Domain Technologies has two USB products.  Audio4-5410 and Audio4-USB.  These use Motorola DSPs.  Primary applications are in the fields of acoustic and audio measurement and analysis, speech processing, vibration measurement and analysis, 3-D sound, signal synthesis, and applications requiring portable field based data acquisition and measurement. 

Lawson Labs has two USB products.  The Model 301 is a complete, Delta-Sigma high-resolution data acquisition system. It serves as a general purpose A/D converter or as a built-in interface for a wide variety of instrumentation. Up to 32 Model 301s can be connected to a single USB port using inexpensive hubs. Two analog input channels are provided, along with eight digital inputs and eight digital outputs.  The Model 302 is a complete, Delta-Sigma high-resolution data acquisition system. It serves as a general purpose A/D converter or as a built-in interface for a wide variety of instrumentation. Up to 32 Model 302s can be connected to a single USB port using inexpensive hubs. Six analog input channels are provided, along with four digital inputs and eight digital outputs.

Arbor Technology Co sells a high-performance USB DAC module, the uDAC-800.  It has 16 single-ended/8 differential inputs with 12-bit resolution.  It supports up to 250K S/s throughput, and up to 330K sample rate.  It has dual 12-bit analog outputs, 16 digital I/O lines, and a general-purpose timer/counter.

IPC Systems Limited (UK)  sells Personal Daq/3000 with these features: 1-MHz, 16-bit multifunction, Synchronous analogue input, analogue output, digital I/O, and counter/timer I/O, 8 differential or 16 single-ended analogue inputs (software selectable per channel), Thermocouple inputs on any of the 8 differential inputs, expandable up to 64SE/32DE analogue inputs, Up to four 16-bit, 1-MHz analogue outputs, 24 high speed digital I/O lines, Four 32-bit counter input channels with quadrature encoder capability.

LabJack.  LabJacks are USB/Ethernet based measurement and automation devices which provide analog inputs/outputs, digital inputs/outputs, and more. They serve as an inexpensive and easy to use interface between computers and the physical world.  Example code is provide in several forms (C++, VB6, VBA, etc.).  Some of their products:
bulletLabJack U3: USB DAQ device with up to 16 12-bit analog inputs, up to 20 digital I/O, up to 2 8-bit analog outputs, up to 2 counters, and up to 2 timers.
bulletLabJack UE9: USB/Ethernet DAQ device with 14 analog inputs (12- to 16-bit), 2 analog outputs (12-bit), 23 digital I/O, 2 counters, and 6 timers. 8 of the digital I/O can be configured on the fly as up to 6 timers and 2 counters.
bulletLabJack UE9-Pro: All the features of the normal UE9 with the addition of an auxiliary low-speed hi-resolution (24-bit) sigma-delta ADC.
bulletLabJack U12: USB DAQ device with 8 12-bit analog inputs, 2 analog outputs, 20 digital I/O, and a 32-bit counter.
bulletadditional accessories are available.

Measurement Computing (now owned by National Instruments, but operating as a separate company).

USB-1208FS Personal Measurement Device™ has these features:
bullet8 A/D channels, 12-bit resolution
bullet8 analog inputs (4 differential or 8 single-ended), 2 10-bit analog outputs
bulletSample rates to 50 ksamples/sec (aggregate)
bullet16 DIO bits,  one counter
bullet1 sync input/output for synchronizing data acquisition between two devices
bulletFully compatible with LabVIEW,™ SoftWIRE®.  It comes with Universal Library™ C++, VB, VB .NET and C# routines (with source)
bulletComes with TracerDAQ a nice oscilloscope/charting package designed specifically for use with the USB-1208FS
bulletThe PMD-1208FS may be used for a wide variety of data acquisition applications. Compatible with USB 1.1 and 2.0 (Windows XP is suggested for optimal performance)
bulletCost is about $149 (less in quantity)

I have significant experience with the USB-1208FS.  I designed it into a manufacturing PCB test system.  The test system evaluates several operational parameters that require the measurement of the test PCB power consumption under three operational conditions, quiescent (when power supply current should be less than about .01 mA, during a general housekeeping session (when power supply current should be between 1 and 2 mA for a duration of 1-2 mS) and during transmit when the RF system is uploading data to a remote receiver (when power supply current should be between 15 and 25 mA for a duration of 1-2 mS).   The PCB test fails if the quiescent current is too high, or if either housekeeping or transmit currents fall outside of their specified ranges, or if the total current consumption is continuously high, which indicates a processor bus-fault on the PCB.  These devices are battery powered in an encapsulated housing, so current consumption is a primary concern.

I selected the USB-1208FS because the sample rate was sufficient to measure the pulse durations and repetition rates of interest and because the 12-bit dynamic range provided was just sufficient to measure the quiescent current consumption while also allowing the measurement of both transmit and high-level fault currents.  Naturally, there is more involved in the total testing environment than I've described here, but this may give you a flavor of how such a device might be applied.  If you have questions or comments please contact me by email.  Here is a screen shot of the tester in action.

If your performance requirements a not as high, consider the Measurement Computing USB-1208LS.  It has these features:
bullet8 A/D channels, 12-bit resolution
bullet8 analog inputs, 2 analog outputs
bulletSample rates to 1.2 ksamples/sec (8kS/s for 4000 samples)
bullet16 DIO bits,  one counter
bulletFully compatible with LabVIEW,™ SoftWIRE®, and Universal Library™ C++ routines , VB, VB .NET and C# (with source)
bulletThe PMD-1208LS may be used for a wide variety of data acquisition applicationss. Compatible with USB 1.1 and 2.0
bulletCost is about $100 (less in quantity)

Pulse/Event Counter

I've often been asked how to implement an event (pulse) counter.  If the pulse repetition rate exceeds about 100 pps, then you need to use external hardware.  Here is an example that uses the 1208 FS.  The maximum practical repetition rate is about 42K pps, which would meet many industrial needs.  This project uses VB 2008 (the Express version is fine).  Download the source code here.

Here is another Measurement Computing based project that I have completed

The requirements for this project were comparatively low-speed analog data acquisition on five analog channels (fewer than 10 samples per second), and the system also had to control a number of solenoid operated valves to sequence toxic gasses through the system under test.  For this purpose the Measurement Computing miniLab 1008 was selected for data acquisition and control, and the Measurement Computing SSR-RACK08 added for isolated relay drivers to be used to drive the solenoid operated valves.  The following three figures show the simple user interface that drives testing using SO2 and CCl4 gasses to validate the characteristics of carbon filters that are used in industrial processes and safety applications, such as gas masks.

The basic operation sequence is

  1. Turn on the SO2 supply to all cartridges to be tested and select cartridge 1 output as input to the SO2 analyzer.  Sample the SO2 concentration and other system values for the configured interval (perhaps 60 seconds).  Record the results to a log file for cartridge 1.
  2. Switch SO2 analyzer input to cartridge 2 and allow the contaminants to clear the analyzer stream (perhaps 5 seconds).  Then repeat the process in step 1 for recording sample data to a log file for cartridge 2.
  3. Switch the analyzer to cartridge 3 (and subsequently to cartridge 4), while repeating the recording process to log files for cartridge 3 then cartridge 4.
  4. If the SO2 concentration from the analyzer exceeds the configured threshold, terminate the test for that particular cartridge and close the associated log file.
  5. Repeat all steps until the SO2 concentration has exceeded the target threshold for all cartridges.

The CCl4 test is done to meat an appropriate ASTM standard for testing carbon filter cartridges.  The CCl4 test is run for a specific time interval, then it terminates automatically.

For more information on these projects, or to discuss similar applications for your own systems, you can contact me directly.

National Instruments DAQPad-6015, DAQPad-6016 (16 analog input, 32 digital I/O, 2 analog output, 2 counter/timers - 200K samples/s), and  NI USB-9215 (four channels of isolated simultaneously sampled analog input, 16-bit/24-bit resolution) are new in the Summer of 2004.  Additional USB units have been added to the NI line during 2005.

Capital Equipment Corp offers the usbDAQ108 (12-bit resolution, 8-analog input channels, two analog outputs, and 12 digital IO lines, up to 10 K samples/sec) and the usbDAQ109 (14-bit resolution and up to 48 K samples per second) at $145 and $245 respectively.

Pico Technology has a line of PC oscilloscope and data acquisition products (USB is the most common interface provided).  SDKs and examples for Visual Basic and other languages are provided for many of these devices.

Pico PC-based digital oscilloscopes offer all the functionality of traditional test equipment (digital storage oscilloscope, spectrum analyzer, meter and data logger), and also many features not normally available in this price range.

By integrating several instruments into one small unit, PC oscilloscopes (PCOs) are lighter and more portable than traditional test equipment. When used with a notebook computer, field engineers can carry a complete electronics lab in their PC.

bulletCompact and portable units
bulletUses your PC monitor to provide a large and detailed color display
bulletSignal storage is limited only by the PC's storage capability
bulletCaptured waveforms and instrument settings can easily be shared with others
bulletNew functionality through free software upgrades
bulletCan be used with desktop or laptop PCs
bulletHardware and software in one package: no compatibility problems or complex set up procedures
bulletUnits are also supplied with PicoLog data logging software, which transforms your PC into a high speed data logger

Pico Data Loggers:

By connecting suitable sensors, Pico data acquisition products can be used to measure temperature, pressure, relative humidity, light, resistance, current, power, speed, and vibration.

Pico data loggers are supplied complete with PicoLog — this powerful but flexible data acquisition software allows you to collect, analyze and display data. With PicoLog the data is viewable both during and after data collection, in both spreadsheet and graphical format. If required, the data can also be exported to other applications.


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Last modified: 11/25/09
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