By Alex Mendelsohn, eeProductCenter Senior Technical Editor
In the world of board-level data acquisition, one trend that stands out is that there really isn't a single trend. Vendors of board-level data acquisition systems offer products that are as diverse as the tasks they're assigned to.
Products are available for systems ranging from sub-sized PC/104 systems to desktop PCI bus plug-ins, to name just a few host bus topologies. On the I/O side, schemes range from Universal Serial Bus to parallel printer ports to LVDS (low-voltage differential signaling).
Size also runs the gamut, from miniature cards that can be embedded into a corner of an OEM design, to full-blown VMEbus form-factor boards that are the centerpiece of a system.
Let's compare two recent data-acq products. One is a high-end high-speed data-acq board for VMEbus assemblages. The other is a slow-speed low-power board intended for embedded applications where slowly changing sensor signals are conditioned.
These two products illustrate how diverse the world of board-level data acquisition and control is. In the near future, we'll focus more closely on families of data acq boards, such as those expressly for PCIbus systems. Watch this column for updates.
Let's start at the high end of our comparison by delving into a recently introduced product from board maker Echotek (Huntsville, Alabama). Echotek's product is an A/D conversion subsystem that resides on a single 6U (six unit) VME 64X slot board. It's priced at about $13,000. Here's what the board looks like; click on the image to see a block diagram.
Click on this image to see a block diagram
As you might guess, this plug-in has the real estate to pack what it takes for very high-speed, high-end data conversion. Moreover, multiple boards can be arrayed for truly high-performance systems.
By itself, one of Echotek's ECAD-2-081500 boards gives you up to two A/D converter channels of operation, and each channel gives you 1.5-GHz A/D conversion (with a resolution of eight bits).
Fast Low-Cost Silicon
Significantly, this board's lightning conversion speed is accomplished using Maxim Integrated Products MAX108 chips. These ICs sell for about $10 or $11 a pop. Nonetheless, Maxim's chips really bring conversion fire to the front ends on these boards.
The MAX108's are PECL-compatible ICs fabbed with bipolar transistors. They also include track-and-hold amplifiers. The on-chip T/Hs sport 2.2-GHz full-power input bandwidth specs, which results in overall high performance (typically 7.5 effective bits) at the Nyquist frequency.
The MAX108s also pack fully differential comparator and decoding circuits on-chip. This touch helps reduce out-of-sequence code errors. Unlike some ultra high-speed A/D chips that can have errors resulting in false full- or zero-scale outputs, the MAX108 limits the error magnitude to one LSB.
Useful For Software Defined Radios
If used as a signal converter, the Echotek ECAD-2-081500's A/D converters can support applications in RF-deck IFs (intermediate frequency) up into the microwave regime. A/D sample rates can be anywhere from 100-MHz to a fast 1.5-GHz.
If you're working with software-defined radios in the 800-MHz to 1-GHz band, for example, an ECAD-2-081500 could replace lots of discrete IF components, filters, mixers, and the like, instead delivering a digitized signal for downstream DSP processing. The 8-bit A/D converter serves adequately at the signal-to-noise ratios typically needed.
On the output side, Echotek's dual-channel board is also fast. It sends gathered data through a dual RACE++ interface, but it also has an LVDS output port, as well as the VME64X interface itself.
On its inputs, you can feed in as many as 128 signals to each channel, via high-speed Mictor connectors. Also, A/D clocking, sync signals, and triggering signals can also be fed in through front-panel-mounted SMA-type coax connectors.
Then there's the ability to configure arrays of these boards. To do that, clocks can be buffered and then distributed to more than one channel, so that multiple channels can be sampled simultaneously. Likewise, sync and trigger signal distribution also permits multiple ECAD-2-081500 digitizer board sets to start acquisitions at the same time.
Another high-end aspect of Echotek's high-end VME board is that each channel is equipped with a FIFO buffer. These are 4-Msamples deep and interface to user-programmable FPGAs.
Each board supports up to three Xilinx Vertex FPGAs/channel, and FPGA options range from 1-million gates to FPGAs with 1.6-million gates. Specifically, you can equip one of these boards with one, two, or three Xilinx XCV1000E FPGAs/channel, or one, two, or three Xilinx XCV1600E FPGAs/channel.
Your FPGA configuration files are also stored in flash, and it's programmable over the VMEbus interface. With that, the FPGAs can let you implement hardware-based---but alterable---DSP, for example. Like the FPGAs, board set-up, and control register loading are accessible through the VME interface.
While you're catching your breath over Echotek's VMEbus board, let's downshift gears and look at an example of a state-of-the-art data-acq board that's at the opposite end of the spectrum. Here's a bird's eye photo of the board. Notice the size of the crystal can.
Onset Computer Corp.'s (Pocasset, Mass.) Tattletale TFX-11v2 board is priced at about $275. This low-power data logger has a very small footprint measuring just only 1.2 x 2.75 inches. Unlike Echotek's screamer, the little Tattletale TFX-11v2 operates at a sampling rate of only up to 6.4-kHz.
However, Onset's TFX-11v2 provides 19 analog channels. Eleven of these give 12-bit resolution, and eight dish up eight bits).
The board also packs 24 digital lines (16 bidirectional and eight that are input-only), as well as dual UARTs (one in software).
Like its distant VMEbus cousin, the Tattletale packs flash: 2-Mbytes worth. In addition to its flash array, the diminutive Tattletale also packs battery-backed RAM that can be used for Read/Write of data and program files.
The Tattletale TFX-11v2 also sports an industrial temperature range that lets it operate from -40°C to +85 °C. In step with embedded-applications that might take it afield, the Tattletale also works over a wide input-voltage range, extending from as low as 5.5-V to as high as 18-V DC.
Its small footprint, low dissipation, adequate I/O, and on-board flash, make the Tattletale TFX-11v2 suitable for applications requiring portability or prolonged field deployment. In that capacity, it can sample over multiple channels and give you the benefit of nonvolatile data storage.
Surprisingly for a low cost, low-end product, the little TFX-11v2 also packs dual processors, housing both a Motorola 68HC11 microprocessor and a Microchip PIC 16F73 microcontroller. Both of these surface-mount devices are user-programmed using Onset's Windows-based TFTools Integrated Development Environment (IDE) called TFBASIC. More on TFBASIC in a moment.
There's more significant silicon, too. The Moto 68HC11 includes an on-chip 8-bit data-converter, but the Tattletale's 12-bit conversions are handled independently by a Texas Instruments Type TLC2543, which, in turn, communicates serially with the 'HC11. The TLC2543 is a switched-cap successive-approximation A/D converter.
When acquiring analog signals, the board's single-ended input range spans zero to 5-V. Ratiometric conversion can be used for gathering data from things such as potentiometers, sensors, and strain gauges (however, you'll likely have to design front-end conditioning circuits or amplifiers for many sensor types, and you may have to use external references as well).
In addition to the usual BASIC commands, TFBASIC also gives you a raft of dedicated commands for Tattletale operations such as assembling 'HC11 code, performing A/D conversion operations, sending data out through a UART, or saving data to flash. TFBASIC also eases entry points into fixed assembly-language routines.
Onset's TFBASIC also supports long integers, string constants, and strings, as well as IEEE-754 single-precision floating-point math. TFBASIC can also be used to throttle the board's power management hooks, with dedicated commands to turn off the 'HC-11 and PIC, leaving only the PIC's timer running.
Get More Information On These Board-Level Products ...
For more details on the Tattletale TFX-11v2 contact Onset Computer Corp., P.O. Box 3450, Pocasset, Mass. 02559-3450. Phone: 800-LOGGERS (800-564-4377) or (508) 759-9500. Fax: (508) 759-9100. E-mail: firstname.lastname@example.org. Click here to access the company's Web site.
For more information on the Echotek's ECAD-2-081500, contact Echotek Corp., 555 Sparkman Dr., Suite 400, Huntsville, Ala.35816. Phone: (256) 721-1911. Fax: (256) 721-9266. Or, go to Echotek's Web site.