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Designing Custom, Low-Cost Instrumentation for Test and Measurement Using Off-the-Shelf FPGA Modules

Thu, 04/29/2010 - 11:36am
Jake Janovetz, Opal Kelly

Designing for industrial applications presents many challenges, but it also allows an engineer to be creative, spread her wings, and explore new technologies to solve the task at hand. Field-Programmable Gate Arrays (FPGAs) and, in particular, commercial off-the-shelf (COTS) FPGA modules can be just the ticket to attack industrial applications that used to be a much more difficult challenge. Development that previously required multiple hardware iterations, taking weeks or months to complete, can now be completed in days by leveraging the rapid prototyping capabilities of FPGAs. One interesting benefit, advocating the use of FPGAs, is that these unprecedented levels of integration allow designers to incorporate custom instrumentation directly into their project. This results in both improved observability and enhanced functionality of the system.

Historically, any number and combination of typical hardware instruments have found a place in industrial applications. Just a few examples include pulse-width modulation, precise timing and event measurement, sensor communication, analog conversion, data acquisition, data logging, real-time filtering, networking, managing sensor ASIC , and test and verification of custom ASICs.

When precision and accuracy are paramount, absolutely nothing compares to the professional application of the high-end test equipment we're all familiar with: oscilloscopes, logic analyzers, signal generators, digital multimeters, precision power supplies, and so on. There are countless scenarios, however, where such precision and accuracy are not required nor justified by the associated cost. In these situations, a simplified instrument can go a long way to achieve the same functionality at a fraction of the cost. Additionally, the savings allow the instrument to be deployed at a scale that would be prohibitive for expensive, precision equipment. Here are a few scenarios that come to mind for such custom instrumentation:

In-house Engineering Support
Many large companies have dedicated groups chartered with building hardware and software tools for improving the performance and efficiency of other internal design groups. Imagine building a suite of small, simple pieces of test equipment such as logic analyzers, signal generators, or application-specific oscilloscopes that could be designed into a product's first-round prototype. These in-situ diagnostic devices would be removed during the transition to production, but could be deployed at the same scale as the prototype units meaning that precious shared lab equipment could be minimized and better used. So, if 25 prototypes are deployed to engineering, each engineer has all of the integrated test equipment on their desk rather than sharing two or three expensive lab analyzers.

Engineers working with the prototypes get added observability afforded by integrated test equipment during this critical design phase and the devices could be re-used on subsequent prototypes and products. They can even get customized functionality from the internal tools group thanks to the flexibility of the FPGA.

Production Line Product Test and Verification
Production lines are often what comes to mind when we think of industrial applications. Engineers are tasked with producing equipment to program, test, and certify their main-line products. The equipment on the production line is often low-volume and highly custom, designed to support high-volume production. The use of FPGAs can dramatically reduce "time to market" of such projects and the low cost of COTS modules means that expensive test equipment on the line can potentially be replaced with much lower cost, custom instrumentation.

As an example of this, a reasonably capable logic analyzer could be designed by an experienced FPGA designer in about a day. Such an instrument would not be as full-featured as a lab logic analyzer, but could be set up with the features necessary for functional test of a particular product. When implemented on a COTS FPGA module, the device could readily rival existing USB-based logic analyzers, cost significantly less, and deployed on the desks of many engineers. For comparison, a mid-grade commercial USB logic analyzer costs around $1,000 while an off-the-shelf USB FPGA module costs less than $300 and can be programmed specifically to the task then reprogrammed for a new task.

Figure 1. The production test rack on the left is composed of expensive, but highly accurate commercial test equipment. The FPGA-based test board on the right is a much lower-cost solution

Integrated Instrumentation in Scientific/Industrial Instruments
Industrial and scientific instrumentation often require built-in diagnostic sensors to monitor precision and performance. A single FPGA can interface to dozens of sensors, analog/digital converters, and other devices to greatly simplify this task. The data can be gathered and analyzed in-place, sent back in real-time to a PC over a USB link for deeper analysis, or simply stored in non-volatile memory for downloading later. 

Figure 2. FPGA module installed in an industrial instrument.


The beauty of the FPGA lies in its ability to act as a hardware chameleon, taking on the personality of hardware implementations where pure software would fail to provide the proper functionality, while enjoying the rapid iterative design cycle that makes software development so popular. Field-programmability is also highly desirable in industrial applications where much of the learning, tweaking, and updating occurs in-situ and under operating conditions, after deployment.

No longer are FPGAs an elite design tool costing hundreds of dollars each and requiring expensive design tools. Extremely capable FPGAs can be had for well under $100 each and the design tools are often freely available on the manufacturer's websites. Off-the-shelf FPGA modules complete with USB and software development kits are available for under $200 and relieve the designer of a significant amount of integration effort. FPGAs allow low-volume, highly custom designs to "ride the coat tails" of higher-volume semiconductor production and reap the low-cost benefits. To further add project security and mitigate risk, FPGA modules eliminate the learning curve for incorporating an FPGA and their often complex power supply and configuration requirements onto a PCB.

FPGAs are tools that should be a part of every electrical engineer's tool belt. Off-the-shelf FPGA modules remove a lot of the risk involved in designing a custom board and still provide most (if not more) of the benefits of using the FPGA alone! The FPGA is now nearly as ubiquitous as the venerable microcontroller; in applicable situations, it should be used with brazen impunity.

For more information, contact Opal Kelly Incorporated, 13500 SW 72nd Ave, Suite 120, Portland, OR 97223; www.opalkelly.com.

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